1. Ch Gases
III. Ideal Gas Law

2. A. Avogadro’s Principle
Equal volumes of gases contain equal numbers of moles
at constant temp & pressure
true for any gas V n

3. UNIVERSAL GAS CONSTANT
A. Ideal Gas Law
Merge the Combined Gas Law with Avogadro’s Principle: PV nT PV T V n
= k
= R
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK
You don’t need to memorize these values!

4. UNIVERSAL GAS CONSTANT
A. Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK
You don’t need to memorize these values!

5. C. Ideal Gas Law Problems
Calculate the pressure in atmospheres of mol of He at 16°C & occupying L.
GIVEN:
P = ? atm
n = mol
T = 16°C = 289 K
V = 3.25 L
R = Latm/molK
WORK:
PV = nRT
P(3.25)=(0.412)(0.0821)(289)
L mol Latm/molK K
P = 3.01 atm

6. C. Ideal Gas Law Problems
Find the volume of 85 g of O2 at 25°C and kPa.
GIVEN:
V = ?
n = 85 g
T = 25°C = 298 K
P = kPa
R = dm3kPa/molK
WORK:
85 g 1 mol = 2.7 mol
32.00 g
= 2.7 mol
PV = nRT
(104.5)V=(2.7) (8.315) (298)
kPa mol dm3kPa/molK K
V = 64 dm3

7. D. Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P
P1 represents the “partial pressure” or the contribution by that gas.
Dalton’s Law is particularly useful in calculating the pressure of gases collected over water.

8. If the first three containers are all put into the fourth, we can find the pressure in that container by adding up the pressure in the first 3:
2 atm
+ 1 atm
+ 3 atm
= 6 atm 1 2 3 4