Ch. 10 Physical Characteristics of Gases

1. Ch. 10 Physical Characteristics of Gases 10.4 Dalton’s Law of Partial Pressure

2. Dalton’s Law of Partial Pressure • John Dalton • responsible for atomic theory • also studied gas mixtures • the P of gas mixture is the sum of the individual pressures of each gas alone • the P that each gas exerts in the mixture is independent of the P that are exerted by other gases

3. Dalton’s Law of Partial Pressure • the total P of a mixture of gases is equal to the sum of partial P of component gases, no matter how many different gases • PT = P1 + P2 + P3 + … • Partial Pressure- P of each gas in mixture

4. Why? • the particles of each gas in a mixture have an equal chance to hit the walls • so each gas exerts P independent of that exerted by other gases • total P is result of the total # of collisions per unit of wall area

5. set for a certain T equal to atmospheric pressure Water Displacement • gas produced is less dense than water so it replaces the water in the bottle • gas collected is not pure because it contains vapor from the water PT = Pgas + Pwater

6. Example • Oxygen gas from decomposition of KClO3 was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0 torr and 20.0°C respectively. If the partial pressure of water vapor is 17.5 torr at 20.0°C, what was the partial pressure of oxygen collected? • PT = PO2 + PH2O • 731.0 torr = PO2 + 17.5 • PO2 = 713.5 torr

7. Example • Find the partial pressure by 2 gases (A and B) mixed if the overall pressure is 790 mmHg. The percent by volume is A: 20% and B: 80%. • PT = PA + PB = 790 mmHg • A: 0.20 x 790 = 158 mmHg • B: 0.80 x 790 = 632 mmHg