A student adds magnesium ribbon to excess dilute hydrochloric acid in an insulated cup. They record the temperature of the mixture every 30 seconds.
| Time (s) | 0 | 30 | 60 | 90 | 120 | 150 |
|---|---|---|---|---|---|---|
| Temperature (∘C^\circ\mathrm{C}∘C) | 20.0 | 24.5 | 27.0 | 26.4 | 25.6 | 24.9 |
Which conclusion is correct?
It is exothermic until 60 s, and after that it becomes endothermic.
It is endothermic, because the temperature falls after 60 s.
It is exothermic; after 60 s the mixture takes in activation energy.
It is exothermic; after 60 s the mixture loses energy to the surroundings.
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.