A student investigates the reaction between citric acid solution and sodium hydrogencarbonate solution.
The student compares two apparatus arrangements. The same volumes and concentrations of the solutions are used in every test. Both solutions start at 20.6 ∘C20.6\ ^{\circ}\text{C}20.6 ∘C in each test. The room and both containers are also at 20.6 ∘C20.6\ ^{\circ}\text{C}20.6 ∘C at the start, and the room stays at this temperature throughout the tests.
| Apparatus | Container | Cover |
|---|---|---|
| P | Polystyrene cup | Lid |
| Q | Glass beaker | No lid |
The student records the lowest temperature reached after mixing. Each test is repeated three times.
| Apparatus | Lowest temperature in repeat 1 (∘C^{\circ}\text{C}∘C) | Lowest temperature in repeat 2 (∘C^{\circ}\text{C}∘C) | Lowest temperature in repeat 3 (∘C^{\circ}\text{C}∘C) |
|---|---|---|---|
| P | 13.1 | 12.9 | 13.0 |
| Q | 14.7 | 14.5 | 14.6 |
Calculate the mean temperature change for each apparatus.
Include a sign in each answer.
Which apparatus is expected to give a mean temperature change closer to the true value?
Explain your answer using the apparatus and the results.
106 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.