1. Ideal Gas Law & Dalton’s Law
Ch. 12 & 13 - Gases
III. Two More Laws
Ideal Gas Law & Dalton’s 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
B. Ideal Gas Law
Merge the Combined Gas Law with Avogadro’s Principle: PV T PV nT 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
B. 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. Ptotal = P1 + P2 + ... D. Dalton’s Law
The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases.
Ptotal = P1 + P

8. D. Dalton’s Law GIVEN: PO2 = ? Ptotal = 1 atm PCO2 = 0.285 torr
Three of the primary components of air are CO2, N2, and O2. In a sample containing only these three gases at a pressure of 1.00 atm, PCO2 = torr and PN2 = torr. What is the partial pressure of O2?
GIVEN:
PO2 = ?
Ptotal = 1 atm
PCO2 = torr
PN2 = torr
WORK:
Ptotal = PCO2 + PN2 + PO2
1 atm = atm atm + PO2
PO2 = atm
= atm
= atm

9. Patm = Pgas + PH2O D. Dalton’s Law
When H2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.
Water exerts a pressure known as water-vapor pressure
So, to determine total pressure of gas and water vapor inside a container, make total pressure inside bottle = atmosphere and use this formula:
Patm = Pgas + PH2O

10. D. Dalton’s Law
Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa.
The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H2 and water vapor.
GIVEN:
PH2 = ?
Ptotal = 94.4 kPa
PH2O = 2.72 kPa
WORK:
Ptotal = PH2 + PH2O
94.4 kPa = PH kPa
PH2 = 91.7 kPa
Look up water-vapor pressure on p.899 for 22.5°C.
Sig Figs: Round to least number of decimal places.

11. D. Dalton’s Law GIVEN: Pgas = ? Ptotal = 742.0 torr PH2O = 42.2 torr
A gas is collected over water at a temp of 35.0°C when the barometric pressure is torr. What is the partial pressure of the dry gas?
The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the “gas” and water vapor.
GIVEN:
Pgas = ?
Ptotal = torr
PH2O = 42.2 torr
WORK:
Ptotal = Pgas + PH2O
742.0 torr = PH torr
Pgas = 700. torr
Look up water-vapor pressure on p.899 for 35.0°C.
Sig Figs: Round to least number of decimal places.