Gas Laws
• The four properties of gases (amount in
moles, volume, temperature, 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 says that at constant T that as the
pressure increases on a gas the volume
decreases.
• 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 = (PV/T)f i and f are initial
and final
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.
• Amount of gas is in moles.
Gas Laws
• One more gas law exists for changes in the gas
properties as well as the amount of gas present in
moles.
• This law is referred to as the Ideal Gas Law
because it accurately predicts gas properties of
ideal gases. Most gases at moderate conditions
behave like an ideal gas.
• Ideal Gas Law
– PV = nRT
– R is the gas constant having a value of .0821 if
using liters, atm, mol, and kelvin temperature.