2.1 – ENERGETICS – PPQ1
Name ………………………………………….……………………………….
1)
Form ………………….
A student added 50.0 cm3 of hydrochloric acid to 50.0 cm3 of sodium hydroxide solution in a polystyrene
cup. The temperature rose by 6.5 C. The initial concentration of each solution was 1.00 mol dm-3.
a) Write an ionic equation for the reaction occurring.
..........................................................................................................................................................................
(1)
b) Calculate the number of moles of acid and alkali used in the reaction.
..........................................................................................................................................................................
..........................................................................................................................................................................
(2)
c) Calculate the heat energy evolved in the reaction. (Assume that the final solution has a specific heat
capacity of 4.18 J g-1 K-1 and a density of 1.00 g cm-3.)
..........................................................................................................................................................................
..........................................................................................................................................................................
(2)
d) Calculate the molar enthalpy change for the reaction.
..........................................................................................................................................................................
..........................................................................................................................................................................
(2)
e) Predict the molar enthalpy change for the reaction for the reaction between sodium hydroxide solution and
nitric acid. Explain your answer.
Prediction ……………………………………………………………………………………………………………….
Explanation ……………………………………………………………………………………………………………..
(2)
(CHM02 Summer 2001)
9
AS.CHEM2.1.008
16-Mar-16
© Ripon Grammar School / RWGrime / AQA
2.1 – ENERGETICS – PPQ2
Name ………………………………………….……………………………….
2)
a) i)
Form ………………….
Define the term standard enthalpy of formation (H f). ………………………………………………………..
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
ii) Write an equation, including state symbols, for the reaction which illustrates the enthalpy of formation of
lithium carbonate.
…………………………………………………………………………………………………………………………. (5)
b) The following table gives some values of standard enthalpies of formation.
Compound
Li2CO3
Na2CO3
Li2O
Na2O
CO2
Hf (kJ mol )
-1216
-1131
-596
-416
-394
-1
Use the data from the table to calculate the enthalpy changes for the decomposition of lithium carbonate and
of sodium carbonate and into the metal oxide and carbon dioxide.
Li2CO3(s)  Li2O(s) + CO2(g)
……………………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………………..
Na2CO3(s)  Na2O(s) + CO2(g)
……………………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………….. (5)
(Ch01 Summer 1996)
10
AS.CHEM2.1.009
16-Mar-16
© Ripon Grammar School / RWGrime / AQA
2.1 – ENERGETICS – PPQ3
Name ………………………………………….……………………………….
3)
a) i)
Form ………………….
Write an equation to represent the enthalpy of formation of butane, C 4H10(g).
………………………………………………………………………………………………………………………..
ii) Calculate the enthalpy of formation of butane, C4H10(g), using the following data.
Hc: C(s) = -394; H2(g) = -286; C4H10(g) = -2877 kJ mol-1
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
b) i)
(4)
Write an equation to represent the enthalpy of combustion of pentane, C 5H12(l).
………………………………………………………………………………………………………………………..
ii) Calculate the enthalpy of combustion of pentane, C5H12(l), using the following data.
Hf: CO2(g) = -394; H2O(l) = -286; C5H12(l) = -173 kJ mol-1
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
c) i)
(4)
Write an equation to represent the enthalpy of combustion of hexane, C6H14(l).
………………………………………………………………………………………………………………………..
ii) Calculate the enthalpy of combustion of hexane, C6H14(l), using the following data.
Hc: C(s) = -394; H2(g) = -286;
Hf: C6H14(g) = -199 kJ mol-1
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………..
(4)
12
AS.CHEM2.1.010
16-Mar-16
© Ripon Grammar School / RWGrime / AQA
2.1 – ENERGETICS – PPQ4
Name ………………………………………….……………………………….
4)
Form ………………….
The table below contains some mean bond enthalpy data.
a) i)
Bond
HH
CC
C=C
NN
NH
Mean bond enthalpy / kJ mol-1
436
348
612
944
388
Write an equation for the formation of one mole of ammonia, NH3, from its elements.
………………………………….....................................................................................................................
ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.
……………………………….........................................................................................................................
……………………………….........................................................................................................................
……………………………….........................................................................................................................
………………………………......................................................................................................................... (4)
b) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in
ethane.
H
H
C
C + H
H
H
H
H
H
H
C
C
H
H
H
H = –136 kJ mol–1
…………………………….................................................................................................................................
…………………………….................................................................................................................................
…………………………….................................................................................................................................
……………………………................................................................................................................................. (3)
c) Explain the term mean bond enthalpy.
…………………………….................................................................................................................................
…………………………….................................................................................................................................
…………………………….................................................................................................................................
……………………………................................................................................................................................. (2)
(CHM2 Winter 2002)
9
AS.CHEM2.1.011
16-Mar-16
© Ripon Grammar School / RWGrime / AQA
2.1 – ENERGETICS – PPQ5
Name ………………………………………….……………………………….
H
5)
a) Ethanal has the structure
H
C
H
Form ………………….
O
C
H
Gaseous ethanal burns as shown by the equation: CH3CHO(g) + 2½O2(g)  2H2O(g) + 2CO2(g)
Use the mean bond enthalpy data given below to answer the following questions.
i)
Bond
Mean bond enthalpy/kJ mol-1
C—H
+413
C—C
+347
C=O
+736
O=O
+498
O—H
+464
Calculate the enthalpy change which occurs when all the bonds in the reactants shown in the above
equation are broken.
………………………………........................................................................................................................
………………………………........................................................................................................................
………………………………........................................................................................................................
………………………………........................................................................................................................
ii) Calculate the enthalpy change which occurs when all the bonds in the products shown in the above
equation are formed.
………………………………........................................................................................................................
………………………………........................................................................................................................
………………………………........................................................................................................................
………………………………........................................................................................................................
iii) Hence, calculate the enthalpy change for the complete combustion of ethanal as shown in the equation
above.
………………………………........................................................................................................................
………………………………........................................................................................................................ (5)
b) State what is meant by the term mean bond enthalpy.
…………………………….................................................................................................................................
…………………………….................................................................................................................................
……………………………................................................................................................................................. (2)
(CHM2 Winter 2002)
7
AS.CHEM2.1.012
16-Mar-16
© Ripon Grammar School / RWGrime / AQA
2.1 – ENERGETICS – PPQ6
Name ………………………………………….……………………………….
6)
Form ………………….
a) Use the mean bond enthalpy data from the table and the equation given below to calculate a value for the
standard enthalpy of combustion of propene. All substances are in the gaseous state.
Bond
C=C
C—C
C—H
O=O
O=C
O—H
Mean bond enthalpy/ kJ mol-1
612
348
412
496
743
463
H
H
H
H
C
C
C
H
+
4 12
O
O
3
O
C
O
+
3 H
O
H
H
…………………………......................................................................................................................................
…………………………......................................................................................................................................
…………………………......................................................................................................................................
…………………………...................................................................................................................................... (3)
b) State why the standard enthalpy of formation, ∆Hf, of oxygen is zero.
…………………………...................................................................................................................................... (1)
c) Use the data from the table below to calculate a more accurate value for the standard enthalpy of
combustion of propene.
Compound
C3H6(g)
CO2(g)
H2O(g)
Standard enthalpy of formation, ∆Hf/ kJ mol-1
+20
–394
–242
…………………………......................................................................................................................................
…………………………......................................................................................................................................
…………………………......................................................................................................................................
…………………………...................................................................................................................................... (3)
d) Explain why your answer to part (b) is a less accurate value than your answer to part (d).
…………………………......................................................................................................................................
…………………………...................................................................................................................................... (2)
e) Define the term standard enthalpy of combustion, ∆Hc
…………………………......................................................................................................................................
…………………………......................................................................................................................................
…………………………...................................................................................................................................... (3)
12