Gas Laws

• The four properties of gases (amount, volume, temperature, and pressure) are all related. A change in any of these will affect one or more of the others.

• The gas laws show the relationship between individual properties and all properties together.

• The first three of these gas laws relate only two variables.

Gas Laws

• • • • 3 of the gas laws deal with the relationship between just two gas properties at a constant number of gas moles.

Boyle’s Law

pressure increases on a gas the volume decreases.

says that at constant T that as the

Charles’ Law

says that at constant P that as the temperature increases the volume increases.

Gay Lussac’s Law

says that at a constant V that as the temperature increases the pressure increases.

Gas Laws

• These 3 laws can be brought together into an equality equation called the combined gas law.

• The relationship between pressure, volume, and temperature is fixed at constant moles.

• PV/T = a constant value • That constant value does not change during individual changes in the properties.

• Therefore (PV/T) i and final = (PV/T) f i and f are initial

Gas Laws

• Attention must be paid to appropriate units in gas equations.

• Pressure can be in any unit as long as it in consistently applied.

• Volume can be in any unit as long as it is consistently applied • Temperature MUST be in Kelvin because it is the only absolute temperature scale.

Gas Laws

• One more gas law exists for changes in the amount of gas (in moles) and its affect on volume. • This law is referred to as

Avogadro’s Law

which states: – For a gas at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles.