Intermolecular forces, Rate of reactions, Chemical equilibrium

Boiling point

The temperature at which the vapour pressure of a substance equals atmospheric pressure. The stronger the intermolecular forces, the higher the boiling point.

Melting point

The temperature at which the solid and liquid phases of a substance are at equilibrium. The stronger the intermolecular forces, the higher the melting point.

Vapour pressure

The pressure exerted by a vapour at equilibrium with its liquid in a closed system. The stronger the intermolecular forces, the lower the vapour pressure.

Heat of reaction (ΔH)

The energy absorbed or released in a chemical reaction.

Exothermic reactions

Reactions that release energy.

Endothermic reactions

Reactions that absorb energy.

Activation energy

The minimum energy needed for a reaction to take place.

Activated complex

The unstable transition state from reactants to products.

Open system

An open system continuously interacts with its environment.

Closed system

A closed system is isolated from its surroundings.

A reversible reaction

A reaction is reversible when products can be converted back to reactants and vice versa.

Chemical equilibrium

It is a dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

Le Chatelier's principle

When the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will oppose the disturbance.