Intermolecular forces, Energy and Changes

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.

Reaction Rate

The change in concentration of reactants or products per unit time.

Collision theory

A model that explains reaction rate as the result of particles colliding with a certain minimum energy to form products.

Catalyst

A substance that increases the rate of a chemical reaction without itself undergoing a permanent change.