IB Chemistry R1.4 Entropy and Spontaneity Key Definitions

Entropy, denoted as $S$, is a thermodynamic property that quantifies the dispersal or distribution of energy and matter in a system.

Gibbs free energy ($\Delta G$) is a thermodynamic property that determines whether a chemical reaction is spontaneous under constant pressure and temperature.

The reaction quotient ($Q$) represents the ratio of product concentrations to reactant concentrations at any point during the reaction:

$$Q = \frac{[\text{products}]}{[\text{reactants}]}$$

A chemical reaction or physical process is spontaneous if it occurs without external intervention under a given set of conditions.

Surroundings are everything outside the system that interacts with it (e.g., the reaction flask, water bath, or air).

The system is the specific part of the universe under study (e.g., the reactants and products involved in the reaction).