A disposable hand warmer contains iron powder. When the packet is opened, the iron reacts with oxygen. The table shows the surface temperature of the hand warmer.
| Time after opening (minutes) | Surface temperature (°C) |
|---|---|
| 0 | 20.0 |
| 30 | 41.5 |
| 300 | 34.0 |
Between 30 minutes and 300 minutes, the hand warmer cools. Suggest two factors that could account for this cooling.
106 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.