More Gases

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

Our atmosphere Since our air is approximately 78%

N2, 21% O2, and 1% other, the total pressure of the air (1 atm) is caused by: 78% N2, or .78 atm 21% O2, or .21 atm 1% other, or .01 atm

You try it If we increase the pressure to 512

kPa, using normal air, what will the partial pressures of N2 and O2 be? (512 kPa)(78%) = 399.36 kPa N2

(512 kPa)(21%) = 109.41 kPa O2

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 O2 and 4 L of H2 is the

correct ratio for making water

If gases are at STP, using 22.4L/mol can determine exact moles of each reactant Determine the volume of N2 and H2 needed

to produce 45 L of NH3

Balance Equation N2 + 3H2 -> 2NH3

Stoichiometry (45 L NH3)(1 L N2/2 L NH3) = 22.5 L N2

(45 L NH3)(3 L H2/2 L NH3) = 67.5 L H2