Further chemical energetics — CIE A-Level Chemistry
1. Unit at a glance
This unit builds on your foundational knowledge of energetics to answer two key questions: why are some ionic compounds more stable than others, and when will a reaction happen spontaneously, regardless of enthalpy change? The learning arc progresses step-by-step: we start with lattice enthalpy for ionic solids, move to entropy (the measure of disorder in a system), and end with Gibbs free energy, the core function that lets you predict reaction spontaneity.
Common Pitfalls
Why: Many students mix up lattice formation and lattice dissociation; breaking is endothermic, but formation of the lattice from ions is exothermic.
Why: Enthalpy change alone does not determine spontaneity; entropy and temperature also affect whether a reaction will occur.