A student mixes dilute hydrochloric acid with sodium hydroxide solution in a polystyrene cup and measures the temperature rise.
| Experiment | Acid | Alkali | Temperature rise / ∘C^\circ\mathrm{C}∘C |
|---|---|---|---|
| 1 | 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 of 1.0 mol dm−31.0\,\mathrm{mol\,dm^{-3}}1.0moldm−3 HCl | 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 of 1.0 mol dm−31.0\,\mathrm{mol\,dm^{-3}}1.0moldm−3 NaOH | 6.8 |
| 2 | 50.0 cm350.0\,\mathrm{cm^{3}}50.0cm3 of 1.0 mol dm−31.0\,\mathrm{mol\,dm^{-3}}1.0moldm−3 HCl | 50.0 cm350.0\,\mathrm{cm^{3}}50.0cm3 of 1.0 mol dm−31.0\,\mathrm{mol\,dm^{-3}}1.0moldm−3 NaOH | ? |
| 3 | 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 of 2.0 mol dm−32.0\,\mathrm{mol\,dm^{-3}}2.0moldm−3 HCl | 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 of 1.0 mol dm−31.0\,\mathrm{mol\,dm^{-3}}1.0moldm−3 NaOH | ? |
Assume that no heat is lost and that all the solutions have the same density and specific heat capacity.
What are the expected temperature rises in experiments 2 and 3?
experiment 2: 13.6 ∘C13.6\,^\circ\mathrm{C}13.6∘C; experiment 3: 13.6 ∘C13.6\,^\circ\mathrm{C}13.6∘C
experiment 2: 13.6 ∘C13.6\,^\circ\mathrm{C}13.6∘C; experiment 3: 6.8 ∘C6.8\,^\circ\mathrm{C}6.8∘C
experiment 2: 6.8 ∘C6.8\,^\circ\mathrm{C}6.8∘C; experiment 3: 13.6 ∘C13.6\,^\circ\mathrm{C}13.6∘C
experiment 2: 6.8 ∘C6.8\,^\circ\mathrm{C}6.8∘C; experiment 3: 6.8 ∘C6.8\,^\circ\mathrm{C}6.8∘C
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.