Hand warmers and instant cold packs use changes that transfer heat energy to or from the surroundings.
A student adds four different solids, A, B, C and D, to separate samples of water. The table shows the student's results.
| Solid | Start temperature / °C | End temperature / °C |
|---|---|---|
| A | 20.0 | 27.5 |
| B | 20.5 | 14.0 |
| C | 19.5 | 24.0 |
| D | 20.0 | 18.5 |
State what is meant by an exothermic change.
Use the table to answer these questions.
Calculate the temperature change for solid A.
Give the letters of the two solids that dissolve endothermically.
Which solid would be best to use in an instant cold pack? Give a reason for your answer.
State what happens to the temperature of the surroundings during an endothermic change.
53 exam-style questions on Edexcel GCSE Chemistry 8.2 Heat energy changes in chemical reactions, covering 8.2.1 Exothermic and endothermic changes, 8.2.2 Bond breaking, bond making and overall energy change, 8.2.3 Calculating energy change from bond energies, and 8.2.4 Activation energy and reaction profiles. Each one has a worked solution and a mark scheme showing where the marks go.