1. Gas Laws Robert Boyle Jacques Charles Amadeo Avogadro
Joseph Louis Gay-Lussac

2. The Combined Gas Law
The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.

3. Boyle’s Law
Pressure is inversely proportional to volume when temperature is held constant.

4. Charles’s Law
The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.
(P = constant)
Temperature MUST be in KELVIN!

5. Avogadro’s Law
For a gas at constant temperature and pressure (STP), the volume is directly proportional to the number of moles of gas (at low pressures).
V = an
a = proportionality constant
V = volume of the gas
n = number of moles of gas

6. PV = nRT Ideal Gas Law P = pressure in atm V = volume in liters
n = moles
R = proportionality constant
= L atm/ mol·K
T = temperature in Kelvin
Holds closely at P < 1 atm

7. Example
What is the pressure in atm of a mol sample of He gas at a temp of 293 K if its volume is
0.505 L?
You can find the density of a gas using the ideal gas law! Let’s see how.

8. Density and the Ideal Gas Law
Combining the formula for density with the Ideal Gas law, substituting and rearranging algebraically:
M = Molar Mass
P = Pressure
R = Gas Constant
T = Temperature in Kelvins

9. Gas Density
… so at STP…

10. Gas Stoichiometry #1
If reactants and products are at the same conditions of temperature and pressure, then mole ratios of gases are also volume ratios.
3 H2(g) N2(g)  NH3(g)
3 moles H mole N  moles NH3
3 liters H liter N  liters NH3

11. Gas Stoichiometry #2 3 H2(g) + N2(g)  2NH3(g)
How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen?
3 H2(g) + N2(g)  2NH3(g)
12 L H2 2
L NH3
= L NH3
8.0 3
L H2

12. Gas Stoichiometry #3
How many liters of oxygen gas, at STP, can be collected from the complete decomposition of 50.0 grams of potassium chlorate?
2 KClO3(s)  2 KCl(s) + 3 O2(g)
50.0 g KClO3
1 mol KClO3
3 mol O2
22.4 L O2
g KClO3
2 mol KClO3
1 mol O2
= 13.7 L O2

13. Gas Stoichiometry #4
How many liters of oxygen gas, at 37.0C and atmospheres, can be collected from the complete decomposition of 50.0 grams of potassium chlorate?
2 KClO3(s)  2 KCl(s) + 3 O2(g)
50.0 g KClO3
1 mol KClO3
3 mol O2
0.612 =
mol O2
g KClO3
2 mol KClO3
= 16.7 L

14. Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P
This is particularly useful in calculating the pressure of gases collected over water.