# Gases

PV = nRT

## Diffusion and Effusion

Diffusion is the rate at which two gases mix.

Effusion is the rate at which a gas escapes through a pin hole.

## Graham’s law of diffusion or effusion

Graham’s law states that the rate of effusion or of diffusion of a gas is inversely proportional to the square root of its molecular weight.

R₁/R₂ = √(M₂/M₁)

In the same conditions of temperature and pressure, the molar mass is proportional to the mass density. Therefore the rate of diffusion of different gases is inversely proportional to the square root of their mass densities.

# Solutions

A solution is a homogeneous mixture of two or more substances.

Solute is a substance that is dissolved in the solution.

Solvent is the substance that dissolves the solute. Solvent is present in greater amount.

## Concentration

Concentration is the ratio of solute and solvent.

Concentration can be measured using molarity, molality and mole fraction.

Molarity (M) = (moles of solute)/(liters of solution)

Molality (m) = (moles of solute)/(kg of solvent)

The mole fraction of a component in solution is the number of moles of that component divided by the total number of moles of all components in the solution.