Energy Change & Rates of RXN Definitions

Activated complex

An activated complex is a high energy, unstable, temporary transition state between the reactants and the products.

Activation energy

The kinetic energy required to form the activated complex.

Catalyst

A substance that increases the rate of the reaction but remains unchanged at the end of the reaction.

Endothermic reactions

Reactions which transform thermal energy into chemical potential energy.

Exothermic reactions

Reactions which transform chemical potential energy into thermal energy.

First law of thermodynamics (Conservation law of energy)

Energy can be converted from one form to another, but it is neither created nor destroyed.

Heat of reaction (enthalpy)

The net change of chemical potential energy of the system.

Reaction rate

The change in concentration per unit time of either a reactant or product.