Question 3
HMethane and hydrogen can both be used as fuels.
Methane: CH₄ + 2O₂ → CO₂ + 2H₂O
Hydrogen: 2H₂ + O₂ → 2H₂O
The diagram shows the two equations using displayed formulae.
The table shows some bond energies.
| Bond | Bond energy (kJ/mol) |
|---|---|
| C–H | 412 |
| O=O | 498 |
| H–H | 436 |
| C=O | 799 |
| O–H | 465 |
a.[3]
Calculate the energy change for the combustion of methane, as shown in the equation.
b.[2]
Calculate the energy change for the reaction of hydrogen with oxygen, as shown in the equation.
c.[4]
A student says:
"Hydrogen is a worse fuel than methane because its energy change is smaller."
Relative atomic mass (Ar): C = 12.0, H = 1.0
Evaluate the student's statement by calculating the energy given out per gram of each fuel.
d.[1]
A data book gives the energy change for the combustion of methane as −890 kJ/mol.
Suggest one reason why this is different from the value calculated from bond energies.
3.2 Energetics Questions
51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.