1. Dalton’s Law of Partial Pressures Chapter 11 – Section 2 - Physical Characteristics of Gases

2. Dalton’s Law of Partial Pressures Partial Pressure: – The pressure of each gas in a mixture Dalton’s Law of Partial Pressures – The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases P total =P 1 + P 2 + P 3 +…..

3. Dalton’s Law of Partial Pressures Most often used to determine the pressure of a gas collected by water displacement P atmosphere = P gas + P water Water vapor pressure varies with temperature – can be found on page R63

4. A practice problem Some hydrogen gas is collected over water at 20.0 0 C. The partial pressure of hydrogen is determined to be 742.5 torr. What is the barometric pressure at the time the gas is collected? Barometric pressure = Atmospheric pressure Water vapor pressure is 17.5 torr P atmosphere = P gas + P water P atmosphere = 742.5 + 17.5 P atmosphere = 760.0 torr

5. Your turn! Helium gas is collected over water at 25 o C. What is the partial pressure of the helium, given that the barometric pressure is 750.0 mmHg? 726.2 mmHg

6. Homework Page 371 10+11