1. More Gases

2. Partial Pressures The total pressure of a sample of gas mixture is made up of the pressures of each individual gas If all students pushed against the wall of the classroom, we could measure the total pressure on the wall The total pressure would equal the pressure of the girls pushing plus the pressure of the boys pushing

3. Our atmosphere Since our air is approximately 78% N 2, 21% O 2, and 1% other, the total pressure of the air (1 atm) is caused by: 78% N 2, or.78 atm 21% O 2, or.21 atm 1% other, or.01 atm

4. You try it If we increase the pressure to 512 kPa, using normal air, what will the partial pressures of N 2 and O 2 be? (512 kPa)(78%) = 399.36 kPa N 2 (512 kPa)(21%) = 109.41 kPa O 2

5. Gas Stoichiometry If gases used in a reaction are at the same temperature and pressure, the volume ratios of the gases will be the ratio of moles of gas This will not give the exact quantities of gases, just the ratios Using 2 L of O 2 and 4 L of H 2 is the correct ratio for making water

6. If gases are at STP, using 22.4L/mol can determine exact moles of each reactant Determine the volume of N 2 and H 2 needed to produce 45 L of NH 3 Balance Equation N 2 + 3H 2 -> 2NH 3 Stoichiometry (45 L NH 3 )(1 L N 2 /2 L NH 3 ) = 22.5 L N 2 (45 L NH 3 )(3 L H 2 /2 L NH 3 ) = 67.5 L H 2