A student investigates three reactions, P, Q and R.
For each reaction, the student adds a solid to a solution and measures the temperature at the start and after 2 minutes.
The table shows the results.
| Reaction | Temperature at start (°C) | Temperature after 2 minutes (°C) |
|---|---|---|
| P: zinc powder + copper sulfate solution | 21 | 35 |
| Q: sodium hydrogencarbonate + citric acid solution | 21 | 12 |
| R: magnesium ribbon + dilute sulfuric acid | 21 | 30 |
Calculate the temperature change for reaction Q.
Which reaction would be the best to use in a cold pack?
Give a reason for your answer.
Describe a method the student could use to get these results and explain what the results show about reactions P, Q and R.
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.