A technician tests four reactions in identical insulated containers to find a reaction for cooling temperature-sensitive reagents. The same volume of mixture is used in each trial. The table shows the starting temperature and the lowest temperature reached in three trials for each reaction.
| Reaction | Trial 1: starting temperature in ∘C^\circ\text{C}∘C | Trial 1: lowest temperature in ∘C^\circ\text{C}∘C | Trial 2: starting temperature in ∘C^\circ\text{C}∘C | Trial 2: lowest temperature in ∘C^\circ\text{C}∘C | Trial 3: starting temperature in ∘C^\circ\text{C}∘C | Trial 3: lowest temperature in ∘C^\circ\text{C}∘C |
|---|---|---|---|---|---|---|
| A | 20.0 | 16.8 | 20.0 | 16.6 | 20.0 | 16.7 |
| B | 20.2 | 13.9 | 20.0 | 14.2 | 20.1 | 14.0 |
| C | 19.8 | 10.2 | 20.1 | 10.7 | 20.0 | 10.4 |
| D | 20.1 | 12.6 | 19.9 | 12.7 | 20.2 | 12.9 |
Calculate the mean temperature fall for each reaction. Give your answers to 1 decimal place.
The reaction selected must give a mean temperature fall of at least 7.0 ∘C7.0\ ^\circ\text{C}7.0 ∘C. The mixture must not fall below 12.0 ∘C12.0\ ^\circ\text{C}12.0 ∘C in any trial.
Explain which reaction should be selected. In your answer, explain the energy transfer and compare the energy of the products with the energy of the reactants.
85 exam-style questions on AQA GCSE Chemistry 5.1 Exothermic and endothermic reactions, covering 5.1.1 Energy transfer during exothermic and endothermic reactions, 5.1.2 Reaction profiles, and 5.1.3 The energy change of reactions. Each one has a worked solution and a mark scheme showing where the marks go.