A student mixes four pairs of substances and records the temperature before and after mixing.
| Mixture | Substances mixed | Start temperature / ∘C^\circ\mathrm{C}∘C | Final temperature / ∘C^\circ\mathrm{C}∘C |
|---|---|---|---|
| P | citric acid solution and sodium hydrogencarbonate | 19.5 | 14.0 |
| Q | dilute hydrochloric acid and sodium hydroxide solution | 19.0 | 25.5 |
| R | ammonium chloride and water | 20.0 | 15.5 |
| S | zinc powder and copper sulfate solution | 18.5 | 27.0 |
Statement 1: P and R both take in heat energy from the surroundings.
Statement 2: In Q, the products store more energy than the reactants did.
Statement 3: S has the largest temperature change, so S is the only mixture in which more energy is released making bonds than is used breaking bonds.
Which statements are correct?
1 only
1 and 2 only
1 and 3 only
2 and 3 only
94 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.