Activation energy

Activation energy is the energy barrier reactants must overcome to reach a reaction’s transition state. It helps determine how quickly a reaction proceeds at a given temperature.

Transition state: A transient, highest-energy arrangement of atoms along a reaction pathway. Activation energy measures the energy gap between reactants and this arrangement.
Chemical kinetics: The study of reaction rates and the factors that influence them. Activation energy is inferred from how reaction rates vary with temperature.
Chemical reaction rate: The change in concentration of a reactant or product per unit time. A higher barrier generally means fewer molecules react per unit time at the same temperature.
Reaction enthalpy: The enthalpy difference between products and reactants in a chemical reaction. It measures the net energy change, whereas activation energy measures the uphill barrier.
Arrhenius equation: An equation relating a reaction-rate constant to temperature and activation energy. It quantifies how the barrier and temperature together affect reaction rate.
Chemical reaction: A process that transforms chemical substances into different substances through rearrangement of atoms. The barrier separates the starting substances from a reaction’s product-forming pathway.
Enzyme catalysis: The acceleration of biochemical reactions by enzymes through binding and stabilizing reaction pathways. Enzymes accelerate reactions by lowering the effective barrier to the transition state.
Reaction Gibbs energy: The Gibbs free-energy difference between products and reactants under specified conditions. It predicts thermodynamic favorability, not how high the pathway’s barrier is.
Reaction coordinate: A progress variable that traces changes in molecular structure along a reaction pathway. Energy profiles plot the activation barrier against progress along this coordinate.
Enthalpy: A thermodynamic state function equal to a system’s internal energy plus pressure times volume. Reaction enthalpy compares reactants and products, not the height of the activation barrier.

Linked from 42 pages