Unit 1 – Energetics
Unit 1 - Jan 2009
Q1.
 Given the following data:

select the expression which gives the enthalpy change, in kJ mol−1, for the reaction:

   A     (−820 × ½) + 270 = −140
   B     (+820 × ½) − 270 = +140
   C     −820 + (270 × 2) = −280
   D     +820 − (270 × 2) = +280

Q2.
 The standard enthalpy change, ΔH1 , for the decomposition of potassium hydrogencarbonate, KHCO3, is impossible to determine directly.

The value of ΔH1 can be calculated from the standard enthalpy changes which accompany the reactions below:

Procedure:
·	The solids were added to separate 30 cm3 portions of dilute hydrochloric acid.  The acid was in excess for both solids.
·	The maximum temperature change for each experiment was noted. 
Results:

·	The following results were obtained with KHCO3(s).

Mass of KHCO3 used = 2.00 g

Temperature change = −4.9 °C
·	The experiment with K2CO3(s) gave a ΔH3 value of −34 kJ mol−1.Assumption:
·	The dilute hydrochloric acid solution has a density of 1 g cm−3.

(a)  (i)   Calculate the heat energy absorbed, in joules, by the reaction of the KHCO3(s) with the solution of dilute hydrochloric acid.
Use the expression
energy absorbed (J)   =   mass of solution  ×  4.18  ×  temperature change
(1)

(ii)   Calculate the number of moles of KHCO3(s) used.  Assume that the molar mass of KHCO3(s) is 100 g mol−1.
(1)

(iii)   Use your answers to (a)(i) and (ii) to calculate, in kJ mol−1, the enthalpy change when one mole of KHCO3(s) reacts completely with the acid (i.e. ΔH2). Include a sign in your answer.
(2)

(b)  A Hess Cycle based on these reactions is shown below.

(i)   Apply Hess's Law to obtain an expression for ΔH1 in terms of ΔH2 and ΔH3
(1)
ΔH1=

(ii)   Use your answers to (a)(iii) and (b)(i), and the ΔH3 value of −34 kJ mol−1, to
        calculate a value for ΔH1 in kJ mol−1.  Include a sign in your answer.
(2)

(c)  The maximum errors for the apparatus used in the experiment with the KHCO3(s) were as follows:
Balance                       0.01g
Measuring cylinder      0.5 cm3
(i)   Calculate the maximum percentage error in using each of the following pieces of apparatus in the KHCO3(s) experiment:
(2)
Balance

Measuring cylinder

(ii)   Suggest a piece of apparatus that could have been used to measure the volume of dilute hydrochloric acid more accurately in this experiment.
(1)
      ..............................................................................................................................................

Q3. 
The standard enthalpy changes of combustion of carbon, hydrogen and methane are
 shown in the table below.

Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol−1?

   A     394 + (2 × 286) − 891
   B     −394 − (2 × 286) + 891
   C     394 + 286 − 891
   D     −394 − 286 + 891
Q4.
This question is about some standard enthalpy changes, ΔH
A     enthalpy of reaction
B     enthalpy of combustion
C     mean bond enthalpy
D     bond enthalpy

(a)  Which enthalpy change is represented by p?

(1)
   A
   B
   C
   D

(b)  Which enthalpy change is represented by q?

(1)
   A
   B
   C
   D

(c)  Which enthalpy change is represented by r?

(1)
   A
   B
   C
   D
Unit 1 - Jun 2009
Q5.
 Some mean bond enthalpy values are given in the table below.

What is the enthalpy change for the reaction shown below in kJ mol−1?

   A     +436 + 151 − 299              =    +288
   B     −436 − 151 + 299              =    −288
   C     +436 +151 − (2 × 299)      =    −11
   D     −436 − 151 + (2 × 299)     =    +11

Q6.
 Propanone, C3H6O, undergoes complete combustion to form carbon dioxide and water.

(a)  In an experiment to calculate the enthalpy change of combustion for propanone, 2.90 g of propanone was burned completely in oxygen. The heat energy from this combustion raised the temperature of 200 g of water from 20.2 °C to 78.4 °C.
The specific heat capacity of water is 4.18 J g−1°C−1.

(i)  Calculate the number of moles of propanone present in 2.90 g.
[The molar mass of propanone is 58 g mol−1.]
(1)

(ii)  Use the expression

to calculate the heat energy transferred to raise the temperature of 200 g of water
 from 20.2 °C to 78.4 °C.
(2)

(iii)  Use your answers to (a)(i) and (ii) to calculate a value for the enthalpy change of combustion of propanone.  Give your answer to three significant figures and include a sign and units.
(3)

(b)  In another experiment, the enthalpy change of combustion for butanone, C4H8O, was found to be −1300 kJ mol−1.

        A Data Book value for the standard enthalpy change of combustion for butanone is −2440 kJ mol−1.
(i)  Suggest a reason why the value obtained in the experiment is so different from the Data Book value.
(1)
 ............................................................................................................................................. 
(ii)  This Data Book value (−2440 kJ mol−1) refers to the following equation.

How would the value be different if it referred to the formation of water in the
gaseous state?  Justify your answer.
(2)
Difference
 ............................................................................................................................................. 
Justification
 ............................................................................................................................................. 
............................................................................................................................................. 
(c)  Standard enthalpy changes of combustion can be used to calculate the standard enthalpy change of formation of a compound.
(i)  Define the term standard enthalpy change of formation, making clear the meaning of standard in this context.
(3)
............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(ii)  Use the standard enthalpy changes of combustion, ΔHc, given in the table
       below to find the standard enthalpy change of formation for ethanoic acid,
       CH3COOH, in kJ mol−1.

(3)

Unit 1 - Jan 2010
Q7.
 Which equation represents the reaction for which the enthalpy change is the standard enthalpy change of formation, ΔHf, of sodium nitrate, NaNO3?
   A      2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
   B      Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
   C      Na(s) + N(g) + 3O(g) → NaNO3(s)
   D      Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

Q8.
 Which equation represents the reaction for which the enthalpy change, ΔH, is the mean
 bond enthalpy of the C–H bond?
   A      ¼CH4(g) → ¼C(g) + H(g)
   B      CH4(g) → C(s) + 2H2(g)
   C      CH4(g) → C(g) + 4H(g)
   D      CH4(g) → C(g) + 2H2(g)

Unit 1 - Jan 2010
Q9.
This question is about hexane, C6H14, and hex-1-ene, C6H12.
(a) What test would you use to distinguish between hexane and hex-1-ene? Give the results of the test for each substance.
(2)
Test:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Result with hexane:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Result with hex-1-ene:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(b) Hex-1-ene has a number of isomers, including two stereoisomers of hex-2-ene.
(i) Complete the formula to show the structure of E-hex-2-ene.
(1)

*(ii) Explain why stereoisomerism can occur in alkenes, and why hex-2-ene has stereoisomers but hex-1-ene does not.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (c) The enthalpy change of combustion of hexane was measured using a spirit burner to heat a known mass of water in a calorimeter. The temperature rise of the water was measured. The results of the experiment are shown below.

The specific heat capacity of water is 4.18 J g−1°C−1.
(i) Calculate the energy in joules produced by burning the hexane. Use the expression energy transferred = mass x specific heat capacity x temperature change.
(1)

(ii) Calculate the enthalpy change of combustion of hexane. The mass of 1 mole of hexane is 86 g.  Give your answer to TWO significant figures. Include a sign and units in your answer.
(3)

(iii) The value for the enthalpy change of combustion in this experiment is different from the value given in data books. Suggest TWO reasons for this difference.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 (iv) A student suggested that the results would be more accurate if a thermometer which read to 0.1°C was used. Explain why this would not improve the accuracy of the result. A calculation is not required.
(1)
 ............................................................................................................................................. 
 ............................................................................................................................................. 

(d) Hex-1-ene can be converted to hexane in the following reaction.

(i) What catalyst is used in this reaction?
(1)
 ............................................................................................................................................. 
(ii) The enthalpy change of this reaction ΔHreaction can be calculated from the following enthalpy changes of combustion.

     Complete the Hess cycle by adding labelled arrows. Use your cycle to calculate the enthalpy change ΔHreaction.
(3)

(iii) The enthalpy change for the reaction of some other alkenes with hydrogen is shown below.

     Explain why the values are so similar.
(1)
 ............................................................................................................................................. 
............................................................................................................................................. 

Unit 1 - Jun 2010
Q10.

Q11.
 This question is about methanol and the energy changes that accompany some of its reactions.
(a) Complete the diagram (using dots and crosses) to show the bonding in methanol, CH3OH. You should show outer electrons only.
(2)

(b) The Hess cycle below can be used to calculate the standard enthalpy change of
       combustion of methanol, using standard enthalpy changes of formation.

(i) Complete the cycle by filling in the empty box.
(2)
*(ii) Define the term standard enthalpy change of formation of a compound,
       making clear the meaning of standard in this context.
(3)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
(iii) Use your cycle and the data below to calculate the standard enthalpy change of
       combustion of methanol, ΔHc.

(2)

(c) An experiment was carried out, using the apparatus below, to estimate the standard
       enthalpy change of combustion of methanol.

After burning the methanol for a few minutes, the temperature of water in the beaker had risen by 20.7 °C and the mass of methanol burnt was 0.848 g.
 (i) Calculate the amount of energy transferred to the water.

 Energy transferred (J) = mass of water × 4.18 × temperature change
(1)

(ii) Calculate the number of moles of methanol, CH3OH, burnt during the experiment.
(1)

(iii) Use your answers to (c)(i) and (ii) to calculate the experimental value for the standard enthalpy change of combustion. Include a sign and units in your answer, which should be given to three significant figures.
(1)

(iv) Compare your answers to (b)(iii) and (c)(iii) and give TWO reasons to explain
       any differences.
(2)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 14 marks)
Unit 1 - Jan 2011
Q12.
The enthalpy change for the reaction

is +1648 kJ mol−1. Hence the mean bond enthalpy for the C–H bond is
   A      +329.6 kJ mol−1
   B      +412.0 kJ mol−1
   C      +1648 kJ mol−1
   D      +6592 kJ mol−1
(Total for question = 1 mark)

Q13.
The enthalpy change of combustion of ethanol was determined using the apparatus shown in the diagram below. In the experiment, the temperature increase of the water in the beaker is measured when a known mass of the ethanol is burned.

(a) The results of the experiment are summarised in the table below.

(i) Calculate the heat energy produced by the combustion of the alcohol using the equation.
 heat energy produced (J) = mass of water x 4.18 x temperature change
(1)
(ii) Calculate the number of moles of ethanol burned in this experiment (the formula of ethanol is C2H5OH).
(3)

(iii) Use the equation below to calculate the enthalpy change of combustion of ethanol in kJ mol−1. Give the value an appropriate sign.
ΔH = heat energy produced ÷ number of moles
(2)

(b) The data book value for the enthalpy change of combustion of ethanol is −1370 kJ mol−1.
(i) Calculate the percentage error in the value calculated in (a)(iii) in comparison with the data book value.
(1)

(ii) List three ways in which the design of the experiment causes the results to be so different from the data book value. (You should be specific but detailed explanations are not required.)
(3)
1
 ............................................................................................................................................. 
2
 ............................................................................................................................................. 
3
 ............................................................................................................................................. 
 (iii) Use the data book values for enthalpy changes of combustion given in the table below to calculate the enthalpy change of formation of ethanol.
(3)

(Total for question = 13 marks)
Unit 1 - Jun 2011
Q14.
For which of the following reactions is the enthalpy change equal to the bond enthalpy of H-I?
   A    
   B    
   C    
   D    
(Total for Question = 1 mark)

Q15.
The enthalpy change for the reaction between hydrochloric acid and sodium hydroxide is −56 kJ mol−1. Therefore
   A    the reaction is exothermic and the temperature rises.
   B    the reaction is exothermic and the temperature falls.
   C    the reaction is endothermic and the temperature rises.
   D    the reaction is endothermic and the temperature falls.
(Total for Question = 1 mark)

Q16.
Copper(II) sulfate exists as blue hydrated crystals and white anhydrous crystals. The enthalpy changes of solution for these two substances may be represented by the following simplified equations:

(a) (i)   Fill in the box and add labelled arrows to complete the Hess cycle to enable you to calculate 
(3)

     (ii)    Calculate a value for the enthalpy change 
(2)
(b) Suggest why it is not possible to directly measure the enthalpy change for the conversion of the blue hydrated copper(II) sulfate crystals into the white anhydrous crystals.
(1)
 ............................................................................................................................................. 
............................................................................................................................................. 
*(c) (i)   
Describe briefly the experimental procedure that you would use to obtain the data necessary to calculate ΔH1, given a known mass of hydrated copper(II) sulfate crystals, CuSO4.5H2O(s).
You should state the apparatus that you would use and any measurements that you would make.
You are not required to calculate the amounts of substances or to explain how you would use the data obtained.
(4)
 ............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
............................................................................................................................................. 
 ............................................................................................................................................. 
     (ii)   The value for the enthalpy change from (c)(i) obtained by experiments in a school laboratory is likely to be significantly different from a data book value.
List three possible reasons for this which do not relate to the quality of the apparatus or chemicals used or possible mistakes in carrying out the procedure.
(3)
1
 ............................................................................................................................................. 
 ............................................................................................................................................. 
2
 ............................................................................................................................................. 
 ............................................................................................................................................. 
3
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for Question = 13 marks)

Q17.
The standard enthalpy changes of formation of some sulfur species are:

The enthalpy of atomization of sulfur is (in kJ mol−1)
   A    103 ÷ 8
   B    279 ÷ 8
   C    279
   D    (103 ÷ 8) + 279
(Total for Question = 1 mark)

Q18.
When a solution of barium chloride is added to sulfuric acid, a white precipitate is formed. The ionic equation (including state symbols) for this reaction is
   A    
   B    
   C    
   D    
(Total for Question = 1 mark)

Unit 1 - Jan 2012
Q19.
If the mean C−−H bond enthalpy is +x, which of the following represents a process with
 an enthalpy change of +4x?
   A      C(g) + 4H(g) → CH4(g)
   B      CH4(g) → C(g) + 4H(g)
   C      CH4(g) → C(s, graphite) + 2H2(g)
   D      C(s, graphite) + 2H2(g) → CH4(g) 
(Total for question = 1 mark)

Q20.
In an experiment performed to measure the enthalpy change for the reaction

3.0 g of zinc powder (an excess) was added to 30.0 cm3 of copper(II) sulfate solution
 of concentration 1.00 mol dm−3. The temperature rise of the mixture was 47.6 K.
 Assuming that the heat capacity of the solution is 4.2 J K−1 g−1, the enthalpy change for
 the reaction is given by
   A      ΔH = −(30 x 4.2 x 47.6) ÷ 0.03
   B      ΔH = −(33 x 4.2 x 47.6) ÷ 0.03
   C      ΔH = −(30 x 4.2 x 47.6) x 0.03
   D      ΔH = −(33 x 4.2 x 47.6) x 0.03
(Total for question = 1 mark)
Q21.
(a) On strong heating, calcium carbonate decomposes to calcium oxide and carbon dioxide:

     Owing to the conditions under which the reaction occurs, it is not possible to measure the enthalpy change directly.
     An indirect method employs the enthalpy changes when calcium carbonate and calcium oxide are neutralized with hydrochloric acid.
     (i) Write the equation for the reaction of calcium carbonate with hydrochloric acid.  State symbols are not required.  [ΔH1 is the enthalpy change for this reaction]
(1)
...................... ΔH1
     (ii) The reaction of calcium oxide with hydrochloric acid is

          Use the equations in parts (i) and (ii) to complete the Hess's Law cycle below to show how you could calculate the enthalpy change for the decomposition of calcium carbonate, ΔHreaction. Label the arrows in your cycle.
(3)

     (iii) Complete the expression for ΔHreaction in terms of ΔH1 and ΔH2 .
(1)
                ΔHreaction = 
(b) Suggest two reasons why the value obtained by carrying out these two experiments
             and using the equation gives a value different to the data booklet value for the
             decomposition reaction of calcium carbonate.
(2)
      ..............................................................................................................................................
      ..............................................................................................................................................
      ..............................................................................................................................................
      ..............................................................................................................................................
(Total for question = 7 marks)

Q22.
The enthalpy change of atomization of iodine is the value of ΔH for the process
   A      I2(s) → I2(g)
   B      I2(s) → 2I(g)
   C      I2(g) → 2I(g)
   D      ½I2(s) → I(g)
(Total for question = 1 mark)

Q23.
The molar enthalpy change of combustion of some alkanes is given below in kJ mol−1.

Another alkane was found to have an enthalpy change of combustion of −6125 kJ mol−1
 The alkane is
   A      C7H16
   B      C8H18
   C      C9H20
   D      C10H22
(Total for question = 1 mark)

Q24.
The enthalpy change for the reaction

cannot be measured directly since some carbon dioxide is always formed in the reaction. It can be calculated using Hess's Law and the enthalpy changes of combustion of graphite and of carbon monoxide.

The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is
   A      −677 kJ mol−1
   B      +111 kJ mol−1
   C      −111 kJ mol−1
   D      +677 kJ mol−1
(Total for question = 1 mark)

Q25.
The concentration of blood glucose is usually given in millimoles per dm3 or
 mmol dm−3. A reading of 5.0 mmol dm−3 is within the normal range. Glucose has a
 molar mass of 180 g mol−1. What mass of glucose dissolved in 1 dm3 of blood would
 give this normal reading?
   A      0.090 g
   B      0.18 g
   C      0.90 g
   D      9.0 g
(Total for question = 1 mark)

Unit 1 - Jun 2012
Q26.
The standard enthalpy changes of formation of carbon dioxide and of methanoic acid are −394 kJ mol−1 and −409 kJ mol−1 respectively. Calculate the enthalpy change for the reaction
H2(g) + CO2(g) → HCOOH(l)
   A    −803 kJ mol−1
   B    −15 kJ mol−1
   C    +803 kJ mol−1
   D    +15 kJ mol−1
(Total for question = 1 mark)
Q27.
In an experiment to determine the enthalpy change of combustion of an alcohol, a spirit burner containing the alcohol was weighed, lit and placed under a copper can containing a known volume of water. The temperature rise of the water was measured and the burner re-weighed. The enthalpy change calculated from the results was much less exothermic than the value reported in the literature.
 Which of the following factors is most likely to be the cause of this error?
   A   Heat loss around the side of the copper can.
   B   The use of a thermometer with a range of 0 - 110 °C rather than 0 - 50 °C.
   C   The use of a measuring cylinder for measuring the water rather than a pipette.
   D   Evaporation of the alcohol during the weighing.
(Total for question = 1 mark)

Q28.
For which of the following changes is the value of ΔH negative?
   A    K(g) → K+(g) + e−
   B    K+Cl–(s) → K+(g) + Cl−(g)
   C    Cl(g) + e− → Cl−(g)
   D    Cl2(g) → 2Cl(g)
(Total for question = 1 mark)

Q29.
(a) State Hess's Law.
(1)
 ............................................................................................................................................. 
............................................................................................................................................. 
(b) Methane burns in a limited supply of oxygen to give carbon monoxide and water.
CH4(g) + 1½O2(g) → CO(g) + 2H2O(l)
The enthalpy change for this reaction cannot be determined directly, but can befound using the standard enthalpy changes of combustion of methane and carbon monoxide, together with Hess's Law.
The standard enthalpy changes of combustion needed are for CH4, -890 kJ mol-1, and for CO, -283 kJ mol-1.
(i) Draw a Hess's Law diagram which would enable you to calculate the enthalpy change for the combustion of methane to carbon monoxide.
CH4(g) + 1½O2(g) → CO(g) + 2H2O(l)
(2)

(ii) Calculate the enthalpy change for this reaction, in kJ mol-1.
(2)

(iii) Explain why the enthalpy change for this reaction cannot be determined directly.
(1)
............................................................................................................................................. 
 ............................................................................................................................................. 
(c) Explain why the calculation in part (b)(ii) would give an incorrect result for the enthalpy change for the reaction below.
CH4(g) + 1½O2(g) → CO(g) + 2H2O(l)
(2)
............................................................................................................................................. 
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 8 marks)

Unit 1 - Jan 2013
Q30.
This question is about the gas ethane, C2H6, and its reactions.
(a)  Write the equation, including state symbols, which represents the reaction taking place when the standard enthalpy change of combustion of ethane is measured.
(2)

(b)  Ethane can react with chlorine to form chloroethane and hydrogen chloride.

Rewrite this equation using displayed formulae.

 Use the equation you have written, together with the bond enthalpy data, to calculate the enthalpy change for the reaction.
(4)

(c)  This reaction takes place in a number of steps, some of which are shown below.

(i)   State the type of reaction occurring in step 1 and the conditions needed for this step.
(2)
Type
 ............................................................................................................................................. 
Conditions
 ............................................................................................................................................. 
(ii)   Complete the equation below for the third step of the reaction, and show the movement of electrons using the appropriate arrows.
(3)

(iii)   Write equations for two termination steps in this reaction.
(2)

(d)  Ethane can be cracked in industry.  Write an equation for the cracking of ethane.
(1)
(e)  Suggest two reasons why cracking of larger alkane molecules is important in industry.
(2)
Reason 1:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
Reason 2:
 ............................................................................................................................................. 
 ............................................................................................................................................. 
(Total for question = 16 marks)

Q31.
In an endothermic reaction in aqueous solution, which of the following is correct?

(Total for question = 1 mark)
Q32.
When 10 cm3 of 2 mol dm−3 hydrochloric acid is reacted with 10 cm3 of 2 mol dm−3 sodium hydroxide solution, the temperature change is ΔT.

When the reaction is repeated with 50 cm3 of each solution, the temperature change is
   A     ΔT
   B     5 × ΔT
   C      × ΔT
   D     10 × 2 × ΔT
(Total for question = 1 mark)

Q33.
The enthalpy change for the reaction to form hydrated sodium thiosulfate crystals cannot be measured directly.
The following Hess cycle can be used.

The enthalpy change for the reaction, ΔHr, is equal to
   A     ΔH1     +   ΔH2
   B     ΔH1     −   ΔH2
   C     −ΔH1   −   ΔH2
   D     −ΔH1   +   ΔH2
(Total for question = 1 mark)
Q34.
In an experiment to measure the enthalpy change of a reaction involving gases, which of the following conditions must always be kept constant?
   A     Pressure
   B     Temperature
   C     Volume
   D     Temperature and pressure
(Total for question = 1 mark)

Unit 1 - Jun 2013
Q35.
Which equation represents the reaction for which the enthalpy change, ΔH, is the mean bond energy of the C-F bond?
   A                CF4(g) → C(g) + 4F(g)
   B              ¼CF4(g) → ¼C(g) + F(g)
   C    C(g) + 4F(g) → CF4(g)
   D    ¼C(g) + F(g) → ¼CF4(g)

(Total for Question = 1 mark)
Q36.
*(a)  Define the term enthalpy change of neutralization.
(2)
 ............................................................................................................................................. 
............................................................................................................................................. 
 ............................................................................................................................................. 
(b)  The enthalpy change of the neutralization reaction between hydrochloric acid, HCl(aq), and sodium hydroxide, NaOH(aq), can be determined by the following procedure.
Procedure:

·	50.0 cm3 of 2.00 mol dm−3 hydrochloric acid is transferred to a polystyrene cup and its temperature recorded
·	50.0 cm3 of 2.00 mol dm−3 sodium hydroxide solution is placed in another polystyrene cup and its temperature recorded
·	The two solutions are mixed, with stirring, and the maximum temperature is recorded
Results:
Initial temperature of both the HCl(aq) and NaOH(aq)         = 19.0 °C                        
Maximum temperature reached after mixing         = 32.5 °C                        
Assumption:
·	The specific heat capacity of all aqueous solutions is 4.18 J g−1 °C−1
·	The density of all aqueous solutions is 1.00 g cm−3
(i)  Calculate the heat energy released (in joules) on mixing the hydrochloric acid and the sodium hydroxide solutions.
Use the expression
energy released (J) = mass of solution × 4.18 × temperature change
(2)

(ii)  Calculate the number of moles of hydrochloric acid used in the experiment.
(1)

(iii)  Give the ionic equation, including state symbols, for the reaction between hydrochloric acid and sodium hydroxide solution.
(1)

(iv)  Use your answers to (b)(i), (ii) and (iii) to calculate the enthalpy change of neutralization for the above reaction. Include a sign and units in your answer.
(3)

(v)  Explain why the enthalpy change of neutralization for the reaction between dilute nitric acid, HNO3(aq), and potassium hydroxide solution, KOH(aq), is predicted to be the same as the enthalpy change of neutralization for the reaction carried out in part (b).
(1)
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(Total for Question = 10 marks)

Q37.
Consider the following information:

For the reaction
H2(g) + I2(g) → 2HI(g)
the enthalpy change, in kJ mol−1, is
   A    +288
   B    +144
   C    −11
   D    −5.5

(Total for Question = 1 mark)

Q38.
The equation for the complete combustion of butanone, C2H5COCH3, is
C2H5COCH3(l) + 5½O2(g) → 4CO2(g) + 4H2O(l)         ΔH = −2440 kJ mol−1

From the above data, the standard enthalpy change of formation of butanone, in kJ mol−1, is
   A    −280
   B    +280
   C    −1760
   D    +1760

(Total for Question = 1 mark)

Q39.
Sodium hydrogencarbonate decomposes on heating to form sodium carbonate. It is difficult to measure the enthalpy change of this reaction directly.
2NaHCO3(s) → Na2CO3(s) + CO2(g) H2O(l)
One method of determining this enthalpy change is to react known amounts of sodium hydrogencarbonate and sodium carbonate, separately, with excess dilute hydrochloric acid.
(a)  0.010 mol of solid sodium hydrogencarbonate was added to 25 cm3 of dilute hydrochloric acid. A temperature rise of 11 °C was measured using a thermometer graduated at 1 °C intervals.
(i)  Calculate the heat energy produced by this reaction using the equation:
Energy transferred in joules = mass × 4.18 × change in temperature
(1)

(ii)  Calculate the standard enthalpy change for the reaction when one mole of sodium hydrogencarbonate reacts with hydrochloric acid.
Remember to include a sign and units with your answer which should be given to three significant figures.
(2)

*(b)  The standard enthalpy change for the reaction between sodium carbonate and dilute hydrochloric acid is found by a similar method to be
ΔH = −321.6 kJ mol−1
Complete the Hess energy cycle below by adding the missing arrow and entities. Use it to calculate the standard enthalpy change for the decomposition of two moles of sodium hydrogencarbonate as in the equation below.
Remember to show your reasoning clearly.
(5)

(c)  The uncertainty for each thermometer reading is ± 0.5 °C.
Calculate the percentage error in the temperature rise of 11 °C.
(1)

(d)  Sodium hydrogencarbonate is used in cooking. Suggest what it is used for and how it works.
(2)
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(Total for Question = 11 marks)

Q40.
Given the following information
CH4(g) → C(g) + 4H(g)          ΔH = +Q kJ mol−1
the mean bond enthalpy for the C—H bond in methane is
   A    +Q
   B    +Q/4
   C    −Q
   D    −Q/4
(Total for Question = 1 mark)
Unit 1 - Jun 2014
Q41.
Consider the following bond enthalpy values.

For the reaction

the enthalpy change, in kJ mol−1, is
   A    −102
   B    +102
   C    +350
   D    +394
(Total for question = 1 mark)

Q42.
1.40 g of an alkene gave 3.77 g of a dichloroalkane on reaction with chlorine.
What is the molecular formula of the alkene?
   A    C2H4
   B    C3H6
   C    C4H8
   D    C6H12
(Total for question = 1 mark)

Q43.
When trichloromethane, CHCl3, reacts with chlorine, the organic product is tetrachloromethane, CCl4. The reaction proceeds by free radical substitution.
The equation for this reaction is
CHCl3 + Cl2 → CCl4 + HCl
(a)  State the essential condition for this reaction to occur at room temperature.
(1)
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(b)  The reaction mechanism involves free radicals. Explain what is meant by the term free radical.
(1)
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(c)  The reaction takes place in a series of steps.
(i)  The initiation step is
Cl2 → 2Cl•
Suggest why this initiation step is more likely than
CHCl3 → CCl3• + H•
(1)
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(ii)  Write equations for the two propagation steps.
(2)
First propagation step

Second propagation step

(iii)  Write an equation for the termination step in which tetrachloromethane is formed.
(1)

(d)  Tetrachloromethane can be manufactured using the by-products of chlorination reactions.
C2Cl6 + Cl2 → 2CCl4
Compare the atom economy of this process with that of the reaction which produces tetrachloromethane from trichloromethane and chlorine. A calculation is not required.
(1)
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(Total for question = 7 marks)

Q44.
 Propane is a saturated hydrocarbon with molecular formula C3H8.
*(a)  Explain the meaning of the terms saturated and hydrocarbon.
(2)
Saturated
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Hydrocarbon
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(b)  Propane is sold in small cylinders for use as a fuel in camping stoves. The enthalpy change of combustion of propane can be measured by experiment using one of these cylinders.
A known mass of propane is burned to heat a container of water, and the temperature rise of the water is measured.
The results of the experiment are shown below.

(i)  How would the mass of propane which was burned be measured?
(1)
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(ii)  Calculate the energy transferred in the experiment, using the results above and the following expression.
Energy transferred (J) = mass × specific heat capacity × temperature change
The specific heat capacity of water is 4.18 J g−1 °C−1.
(1)

(iii)  Calculate the enthalpy change of combustion of propane, ΔHc, in kJ mol−1.
Give your answer to three significant figures and include a sign.
(3)

(iv)  The results of this experiment are inaccurate due to heat loss.
Suggest one other source of error, other than measurement errors and limitations of the equipment.
(1)
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(c)  Another way of calculating the enthalpy change of combustion for propane is to use mean bond enthalpy data.
(i)  Complete the equations in the Hess cycle below. The enthalpy change of +6490 kJ mol−1 is the total energy required to break the bonds in propane and in oxygen.
(1)

(ii)  Use the data in the table to calculate the enthalpy change, Z, in kJ mol−1.

(1)

(iii)  Use the cycle in (c)(i), and your answer to (c)(ii), to calculate the enthalpy change, ΔHx, in kJ mol−1, for the combustion of propane.
(1)

(iv)  The data book value for the standard enthalpy change of combustion, , for propane is −2219.2 kJ mol−1. This value is more exothermic than that calculated using mean bond enthalpy data. Give one reason for this.
(1)
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(Total for question = 12 marks)

Q45.
The standard enthalpy change for the combustion of graphite is −393.5 kJ mol−1 and that of diamond is −395.4 kJ mol−1.
What is the standard enthalpy change for the reaction below, in kJ mol−1?
C(s, graphite) → C(s, diamond)
   A    −1.9
   B    +1.9
   C    −788.9
   D    +788.9
(Total for question = 1 mark)

Q46.
The standard enthalpy change of neutralization when an acid reacts with an alkali is the number of kilojoules released by the
   A    formation of one mole of salt.
   B    formation of one mole of water
   C    neutralization of one mole of acid.
   D    neutralization of one mole of alkali.
(Total for question = 1 mark)

Q47.
The reaction for which the enthalpy change is the standard enthalpy change of formation of water,  is
   A    H2(g) + ½O2(g) → H2O(l)
   B    H2(g) + ½O2(g) → H2O(g)
   C    2H2(g) + O2(g) → 2H2O(l)
   D    2H2(g) + O2(g) → 2H2O(g)
(Total for question = 1 mark)