The difference in energy between the reactants and the transition state is the _____.

In thermodynamics and chemical kinetics, the difference in energy between the reactants and the transition state is referred to as the activation energy (often denoted as $E_a$). Activation energy is the minimum amount of energy required for a chemical reaction to occur. It represents the energy barrier that must be overcome for the reactants to be transformed into products.

Explanation

When a reaction occurs, the reactants must first reach a high-energy state known as the transition state, which is a temporary and unstable arrangement of atoms. This transition state is at a higher energy level than the reactants. The energy difference between this transition state and the energy of the reactants defines the activation energy.

The concept of activation energy is critical for understanding reaction kinetics, as it explains why certain reactions occur faster than others. Factors such as temperature, concentration, and the presence of catalysts can influence the activation energy and, thus, the rate of reaction. For instance, catalysts lower the activation energy, allowing the reaction to proceed more rapidly at a given temperature.