1. Molecular Composition of Gases
Gas and Stoichiometry!

2. Gay-Lussac
Law of combining gases: at constant temperature and pressure, volumes of gaseous reactants and products can be expressed as simple whole number ratios
These numbers are equivalent to the coefficients in a balanced chemical equation

3. Avogadro's Law
Equal volumes of gases at the same temperature and pressure contain equal numbers of particles (molecules)
For example: 2H2 + O2 → 2H2O means 2 volumes of H2 combine with one volume of O2 to make 2 volumes of H2O
For every 2 particles of H2, you need one particle of O2 and create 2 particles of H2O

4. Avogadro's Law
Corollary: gas volume is directly proportional to the number of moles (at constant temperature and pressure)
V=kn
Volume occupied by one mole at STP: L (standard molar volume)

5. Sample problem 11-1
Chemical reaction produces mole of O2. What volume in liters is occupied by this gas at STP?
Known: mole at STP
Calculate: molex L= mole
Then correct for sig dig! L

6. Sample Problem 11-2
Reaction produces 98.0 mL of SO2 at STP. What is the mass of the gas?
Known: mL = L at STP
0.098 L x 1 mole = mole SO L
mole x 64.07g SO2 = g mole

7. More Problems!
You are planning an experiment that requires mole of nitrogen monoxide gas (NO). What volume of this gas would you need at STP?
Suppose you need 4.22 g of chlorine gas (Cl2). What volume (at STP) of this gas would you expect to use?