The Ideal Gas Law
Review
Recall the equation of the constant (k) for each law:
Boyle’s Law
kB = PV
Gay-Lussac’s Law
kG = P/T
Charles’s Law
kC = V/T
Avogadro’s Law
kA = V/n
Review
Recall the equation of the constant (k) for each law:
Boyle’s Law
kB = PV
Gay-Lussac’s Law
kG = P/T
Charles’s Law
kC = V/T
Avogadro’s Law
kA = V/n
Combine the four constants …
A New Constant Emerges
Recall the equation of the constant (k) for each law:
Boyle’s Law
kB = PV
PV
Gay-Lussac’s Law
kG = P/T
nT
Charles’s Law
kC = V/T
Avogadro’s Law
kA = V/n
The Ideal Gas Constant
 The Ideal Gas Constant has the symbol R
R=
PV
nT
The Ideal Gas Equation
 The Ideal Gas Constant has the symbol R
R=
PV
nT
Rearranging this gives the Ideal Gas Law:
PV = nRT
The Ideal Gas Equation
 The Ideal Gas Constant has the symbol R
R=
PV
nT
Rearranging this gives the Ideal Gas Law:
pressure
constant
PV = nRT
moles
volume
temperature
The Ideal Gas Equation
 The Ideal Gas Constant has the symbol R
R=
PV
nT
Rearranging this gives the Ideal Gas Law:
PV = nRT
R = 8.314 kPa L
mol K
The Ideal Gas Equation
 The Ideal Gas Constant has the symbol R
R=
PV
nT
Rearranging this gives the Ideal Gas Law:
PV = nRT
R = 8.314 kPa L
mol K
NOTE: When using this value for R,
Pressure must be in kPa, Volume must be in L ,
and Temperature must be in Kelvin.
Example
1) Calculate the pressure of 0.412 mol of He gas at
16.0°C occupying 3.25 L.
On board
Example
2) When 2.50 g of ethanol, C2H6O, is vaporized, the
vapour is found to have a pressure of 100.2 kPa.
The volume of the container is 1.68 L and the
temperature is 100°C. What is the molar mass of
the ethanol?
Hint – Molar mass is the mass in g’s of 1 mol of a
substance.
What is an ‘Ideal’ gas?
 They don’t exist!!!
What is an ‘Ideal’ gas?
 They don’t exist!!!
 An ‘ideal’ gas is a model for gas behavior that follows
the Kinetic Molecular Theory
- gas particles are in constant movement
- collisions btwn particles and with the container
are elastic
- there are no attractive or repulsive forces btwn
the particles of a gas
- do not condense into liquids when cooled
The Bottom Line
 At ordinary conditions, most gases behave ideally
and obey the gas laws