Ace the AQA GCSE Biology Paper 2: Unleash Your Inner Scientist in 2025!

In a reversible reaction, the energy changes associated with the process are fundamentally linked to the nature of the reaction itself. One direction of the reaction is exothermic, meaning it releases energy into the surroundings, while the reverse direction is endothermic, taking in energy from the surroundings. This duality is crucial because it reflects the principles of thermodynamics, where energy must be conserved and shifts based on the direction of the reaction.

For example, consider a scenario where a substance undergoes a phase change from solid to liquid and then back to solid. The process of melting (solid to liquid) absorbs heat from the environment (endothermic), whereas the freezing (liquid to solid) releases heat (exothermic). This understanding helps clarify that reversible reactions are characterized by the inherent energy exchange depending on the direction of the reaction. Thus, the correct statement about energy changes in reversible reactions is that one direction is exothermic and the other direction is endothermic.