- Glossary
- Practice Exercises
activation energy - the minimum amount of energy particles need to have if a collision between them is to result in a reaction.
catalyst – a substance that increases the rate of a reaction but remains chemically unchanged itself at the end of the reaction.
collision theory - a theory stating that for a reaction to occur the particles must collide, have sufficient energy (at least the activation energy) and collide with the correct orientation.
energy distribution curve – a graph of energy against the number of particles in a sample with those energies. Also called a Maxwell–Boltzmann curve, the energy distribution curve is a representation of the Maxwell–Boltzmann distribution.
enthalpy level diagram – a diagram showing the amount of energy contained in the reaction mixture over time, beginning with the enthalpy of the reactants and ending with the enthalpy of the products. Also called an enthalpy profile diagram.
heterogeneous catalyst – a catalyst in a different phase to the reactants.
homogeneous catalyst – a catalyst in the same phase as the reactants.
kinetic theory – the theory that particles in gases and liquids are in constant movement. The kinetic theory can be used to explain the effect of temperature and pressure on the volume of a gas as well as rates of chemical reactions.
Maxwell–Boltzmann distribution - the characteristic distribution of the energies of particles. Often plotted as a graph, called an energy distribution curve or Maxwell–Boltzmann curve, of energy against the number of particles in a sample with those energies.
order of reaction - the power to which the concentration of a reactant is raised in the rate equation. If the concentration does not affect the rate, the reaction is zero order. If the rate is directly proportional to the reactant concentration, the reaction is first order. If the rate is directly proportional to the square of the reactant concentration.
phase – a region of a physical system with uniform chemical composition or physical properties. For example, ‘the gas phase’ indicates a region composed only of gas.
rate constant is the constant of proportionality in the rate equation.
rate of a reaction is the decrease in concentration of reactants per unit time, or the increase in concentration of products per unit time.
transition state – a state through which a reaction passes between the reactants and the products. It is the state that has the highest energy, represented by the highest point on an enthalpy profile diagram or enthalpy level diagram.