Why may the measured temperature rise be smaller than the true value?
Bond breaking in the reaction releases too much energy
Some heat is transferred to the cup and surroundings
The polystyrene cup transfers heat into the mixture
Mass is not conserved as the solution heats up
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.