A student investigates the reaction between solid barium hydroxide octahydrate and solid ammonium chloride in a sealed vessel. The temperature of the mixture is monitored using a digital probe and is observed to decrease from 294.5 K294.5\text{ K}294.5 K to 261.2 K261.2\text{ K}261.2 K.
State the term used to describe this type of heat energy change.
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.