International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In an energy level diagram for an endothermic reaction, what does ΔH show?

1. The increase in temperature

2. The overall energy change of the system

3. The activation energy required

4. The energy released during the reaction

The correct answer is: The overall energy change of the system

In an energy level diagram for an endothermic reaction, ΔH represents the overall energy change of the system. Specifically, it indicates the difference in energy between the reactants and products. In endothermic reactions, the system absorbs energy from the surroundings, resulting in products that have a higher energy level compared to the reactants. This positive change in enthalpy (ΔH) shows that energy is required for the reaction to proceed, reflecting how much heat energy is absorbed during the reaction. This understanding is essential because it highlights the nature of endothermic reactions—where energy input is necessary for the transformation of reactants into products—contrasting them with exothermic reactions, where energy is released. By clearly understanding ΔH, one can better grasp how reactions interact with their surroundings in terms of energy transfer, which is a fundamental concept in thermochemistry.