A self-heating can uses a reaction to warm food. The reaction must start without heating, so its activation energy must be less than 60 kJ/mol. It must also transfer as much energy as possible to the surroundings.
The table shows information from the reaction profiles of four reactions.
| Reaction | Energy of reactants (kJ/mol\mathrm{kJ/mol}kJ/mol) | Energy at the top of the peak (kJ/mol\mathrm{kJ/mol}kJ/mol) | Energy of products (kJ/mol\mathrm{kJ/mol}kJ/mol) |
|---|---|---|---|
| P | 100 | 150 | 20 |
| Q | 100 | 120 | 140 |
| R | 100 | 130 | -50 |
| S | 100 | 350 | -200 |
Which reaction should be used?
Reaction P
Reaction Q
Reaction R
Reaction S
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.