Assessment and Qualifications Alliance (AQA) GCSE Chemistry Paper 1 Practice Exam

During an exothermic reaction, energy is released into the surroundings, typically in the form of heat. This release of heat energy results in an increase in the temperature of the surrounding environment. As the reaction proceeds, the reactants convert into products, and as a result, the surrounding temperature rises because the energy that was once stored in the chemical bonds of the reactants is now transferred to the surroundings, elevating the temperature.

In contrast, an endothermic reaction would absorb energy, which would lead to a decrease in temperature, and reactions that remain at a constant temperature typically involve phase changes or are at equilibrium. Fluctuations in temperature might occur in non-ideal situations or with specific types of reactions but do not represent the typical behavior of exothermic reactions. Thus, the increase in temperature is a defining characteristic of exothermic processes.