A student investigates the enthalpy changes of four different reactions (PPP, QQQ, RRR, and SSS) using a simple calorimeter. In each experiment, the reactant is added to a known mass of water, and the temperature change is recorded. The results are shown in the table below:
| Reaction | Mass of water / g\text{g}g | Initial temperature / ∘C^{\circ}\text{C}∘C | Final temperature / ∘C^{\circ}\text{C}∘C | Moles of reactant / mol\text{mol}mol |
|---|---|---|---|---|
| PPP | 50.0 | 20.2 | 17.4 | 0.025 |
| QQQ | 100.0 | 19.5 | 22.1 | 0.050 |
| RRR | 50.0 | 18.5 | 23.8 | 0.020 |
| SSS | 100.0 | 21.0 | 16.2 | 0.040 |
Which reaction is exothermic and has a molar enthalpy change (ΔH\Delta HΔH) of approximately -55.4 kJ mol-1? (Assume the specific heat capacity of the aqueous solution is 4.18 J g-1 K-1 and its density is 1.00 g cm-3)
Reaction PPP
Reaction QQQ
Reaction RRR
Reaction SSS
Practise OCR GCSE Chemistry Energetics with exam-style questions for Foundation and Higher tier. 30 questions, matched to the OCR GCSE Chemistry (J248) specification and written in Paper 1 and Paper 2 (Foundation Tier) or Paper 3 and Paper 4 (Higher Tier) style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.