1. Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P

2. Collecting gas over H2O

3. Dalton’s Law of Partial Pressures
For gases collected over water:
Pgas = Patm – PH2O

4. Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)
How many grams of magnesium are required to yield 1.12 liters of H2 collected by displacement of water at 26oC and 748 torr? (Vapor pressure: 3.4 kPa or 25.5 torr)
Mg(s) HCl(aq)  MgCl2(aq) + H2(g)

5. Partial Pressures
Mole Fraction (Xgas)
= mols of gas/total mols of gases in mixture
Xgas = ngas/ntotal

6. Calculate the total pressure (in atm) of a mixture that contains 1
Calculate the total pressure (in atm) of a mixture that contains 1.00 gram of H2 and gram of He in a 5.00-liter container at 21oC. What are the partial pressures of the H2 and He?

7. Two flasks are connected with a stopcock
Two flasks are connected with a stopcock. The first flask has a volume of 5 liters and contains nitrogen gas at a pressure of 0.75 atm. The second flask has a volume of 8 L and contains oxygen gas at a pressure of 1.25 atm. When the stopcock between the flasks is opened and the gases are free to mix, what will the pressure be in the resulting mixture?

8. Practice Problems
How many grams of antimony(III) chloride can be produced from 3570 cm3 of chlorine at STP reacting with an excess of antimony?
2 Sb(s) Cl2(g)  2 SbCl3(s Ans g SbCl3
What volume of oxygen can be collected by displacement of water at 745 torr and 23oC by the complete decomposition of 5.00 g of KClO3? (H2O = 2.8 kPa or 21 torr)
2 KClO3(s) + heat  2 KCl(s) O2(g) Ans liters
What’s the partial pressure of carbon dioxide in a container that holds 5 moles of carbon dioxide, 3 moles of nitrogen, and 1 mole of hydrogen and has a total pressure of 1.05 atm? Ans atm