1. Ch. 13 - Gases Two More Laws (Sec 13.6-13.7)
Gases notes #5 - Dalton's Law & Graham's Law.ppt

2. After this lesson you will:
Know the definition of Dalton’s Law Apply Dalton’s Law to find the partial pressure of a gas in a mixture Know the definition of diffusion and the definition of effusion Know the definition of Graham’s Law Apply Graham’s Law to solve for the molar mass of a gas Apply Graham’s Law to solve for the relative rate of a gas’s particles

3. Ptotal = P1 + P2 + ... 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
When a gas (H2, for example) is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.

4. Dalton’s Law Practice GIVEN: Pgas = ? Ptotal = 742.0 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 = torr
Look up water-vapor pressure on p.424 for 35.0°C.
Sig Figs: Round to least number of decimal places.

5. Graham’s Law Graham’s Law
Rate of diffusion of a gas is inversely related to the square root of its molar mass.
The equation shows the ratio of Gas A’s speed to Gas B’s speed.
You do need to memorize this

6. Put the gas with the unknown speed as “Gas A”.
Graham’s Law Practice
A molecule of oxygen gas has an average speed of 12.3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions?
Put the gas with the unknown speed as “Gas A”.

7. Graham’s Law Practice
An unknown gas diffuses 4.0 times faster than O2. Find its molar mass.
The first gas is “Gas A” and the second gas is “Gas B”
The ratio “A/B” is 4.0
Square both sides to get rid of the square root sign.