Topic questions Energy changes Bond energy calculations
8 questions · 66 marks · about 1.5 hours
Methane reacts with oxygen as shown in the equation:
The table shows some bond enthalpies.
| Bond | O–H | O=O | C=O |
| Bond enthalpy / kJ mol–1 | +464 | +498 | +805 |
What is the bond enthalpy, in kJ mol–1, of the C–H bond in methane?
A +109
B +367
C +435
D +568
This question is about different areas of chemistry.
Why do all average bond enthalpies have a positive value?
Determine the C–H bond enthalpy, in kJ mol–1, using the information above.
C–H bond enthalpy =........ kJ mol–1
Hydrogen gas is being considered as a household fuel to replace methane.
The enthalpy change of formation, 
fH, for H2O(l) is –285.8 kJ mol–1.
Determine the energy released when 60.0 m3 of hydrogen is used as a household fuel at RTP.
Give your answer to 3 significant figures and in standard form.
Compound A is a chloride of a Period 3 element.
A student carries out the 2 steps below to find the formula of compound A.
Step 1 The student adds 5.00 
10–4 mol of compound A to water. A colourless solution is formed.
Step 2 The colourless solution reacts with exactly 60.0 cm3 of 2.50 
10–2 mol dm–3 AgNO3(aq) to form a white precipitate.
Write an ionic equation, with state symbols, for the reaction in Step 2.
Determine the formula of compound A.
Compound B, shown below, is an antiviral medicine.
What is the molecular formula of compound B ?
How many chiral carbon atoms are there in one molecule of compound B ?
Propane, C3H8, (boiling point −42 °C) is used as ‘camping gas’. A student plans to determine the enthalpy change of combustion of propane, 
cH (C3H8), by two methods.
The student first carries out an experiment using the apparatus below.
Determine the enthalpy change of combustion of propane, in kJ mol−1.
Give your answer to 3 significant figures.
cH (C3H8) =........ kJ mol−1
The student finds that the experimental enthalpy change 
cH (C3H8) is much less exothermic than the accurate standard enthalpy change 
cH (C3H8) in databases.
One reason could be that the student’s experiment had not been carried out under standard conditions.
Suggest two other reasons for this difference in enthalpy change.
Sulfuric acid is an important chemical used to make detergents, fertilisers and dyes. It is manufactured in a multi-step process.
In the first step of the manufacture of sulfuric acid, sulfur dioxide, SO2, can be made from the combustion of hydrogen sulfide, H2S, shown in Reaction 1.
Explain why the enthalpy change for Reaction 1 has a negative value.
Use ideas about enthalpy changes associated with bond breaking and bond making.
Some standard entropy values are given below.
| Substance | H2S(g) | O2(g) | SO2(g) | H2O(l) |
S / J K−1 mol−1 | 206 | 205 | 248 | 70 |
Using calculations, explain whether Reaction 1 is feasible at 20 °C.
Calculations
Explanation for feasible or non feasible........
Write an expression for Kp for Equilibrium 1.
Include the units.
Determine the value of Kp for Equilibrium 1 at 1000 K.
Show all your working.
Give your answer to 3 significant figures.
The chemist repeats the experiment in (b) at a different temperature.
The chemist finds that the value of Kp is greater than the answer to (b)(ii).
Explain whether the temperature in the second experiment is higher or lower than 1000 K.
Vanadium(V) oxide, V2O5(s), is used as a catalyst in equilibrium 1.
Explain whether vanadium(V) oxide is acting as a homogeneous or heterogeneous catalyst.
Which enthalpy change(s) is/are endothermic?
1 The bond enthalpy of the C–H bond
2 The second electron affinity of oxygen
3 The standard enthalpy change of formation of magnesium
A 1, 2 and 3
B Only 1 and 2
C Only 2 and 3
D Only 1
Your answer
This question is about enthalpy changes.
Table 16.1 shows enthalpy changes that can be used to determine the enthalpy change of hydration of fluoride ions, F –.
Explain what is meant by the term enthalpy change of hydration.
Calculate the enthalpy change of hydration of fluoride ions, F –.
enthalpy change of hydration =........ kJ mol–1
Predict how the enthalpy changes of hydration of F – and C l – would differ.
Explain your answer.
Fluorine reacts with steam as shown in the equation below.
Average bond enthalpies are shown in the table.
| Bond | Average bond enthalpy / kJ mol–1 |
| O–H | +464 |
| O=O | +498 |
| H–F | +568 |
Explain what is meant by the term average bond enthalpy.
Calculate the bond enthalpy of the F–F bond.
bond enthalpy =........ kJ mol–1
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