Download Molecular Composition of Gases

Molecular Composition of Gases
Gas and Stoichiometry!
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
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
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: 22.41410
L (standard molar volume)
Sample problem 11-1
• Chemical reaction produces 0.0680 mole of O2.
What volume in liters is occupied by this gas at
STP?
• Known: 0.0680 mole at STP
• Calculate: 0.0680 molex22.41410L=1.5241588
1 mole
• Then correct for sig dig! 1.52 L
Sample Problem 11-2
• Reaction produces 98.0 mL of SO2 at STP.
What is the mass of the gas?
• Known: 98.0 mL = 0.098 L at STP
• 0.098 L x 1 mole = 0.004372248 mole SO2
22.41410 L
• 0.004372248 mole x 64.07g SO2 = 0.2801299g
1 mole
More Problems!
• You are planning an experiment that requires
0.0580 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?