An engineer tests four reaction mixtures as possible heat sources. The same volumes and concentrations of solutions are used in identical polystyrene cups with lids.
The engineer records the temperature every 30 seconds.
| Time (s) | Mixture P temperature (∘C^\circ\mathrm{C}∘C) | Mixture Q temperature (∘C^\circ\mathrm{C}∘C) | Mixture R temperature (∘C^\circ\mathrm{C}∘C) | Mixture S temperature (∘C^\circ\mathrm{C}∘C) |
|---|---|---|---|---|
| 0 | 20.0 | 18.0 | 21.0 | 22.0 |
| 30 | 23.0 | 21.5 | 18.5 | 25.0 |
| 60 | 26.0 | 25.0 | 16.0 | 28.0 |
| 90 | 25.5 | 27.5 | 14.5 | 30.5 |
| 120 | 25.0 | 27.0 | 15.0 | 30.0 |
| 150 | 24.5 | 26.5 | 15.5 | 29.5 |
Which mixture should the engineer select to transfer the most energy to the surroundings?
Explain your answer using the results.
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.