Gas Laws: GasStoichiometry

At the conclusion of our time together, you should be able to:

1. Use the Ideal Gas Law to solve a gas stoichiometry problem.

Gases and Stoichiometry

2 H2O2 (l) ---> 2 H2O (g) + O2 (g)

Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?

Bombardier beetle uses decomposition of hydrogen peroxide to defend itself.

Gases and Stoichiometry

2 H2O2 (l) ---> 2 H2O (g) + O2 (g)

Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?

Solution1.1 g H2O2 1 mol H2O2 1 mol O2 22.4 L

O2

34 g H2O2 2 mol H2O2 1 mol O2

= 0.36 L O2 at STP

Gas Stoichiometry: Practice!

How many grams of He are present in 8.0 L of gas at STP?

= 1.4 g He

8.0 L He x 1 mol He

22.4 L He

x 4.00 g He

1 mol He

Gas Stoichiometry Trick

If reactants and products are at the same conditions of temperature and pressure, then mole ratios of gases are also volume ratios.

3 H2(g) + N2(g) 2NH3(g)

3 moles H2 + 1 mole N2 2 moles NH3 67.2 liters H2 + 22.4 liter N2 44.8 liters NH3

Gas Stoichiometry Trick Example

How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen in a closed container at constant temperature?

3 H2(g) + N2(g) 2NH3(g)

12 L H2

L H2

= L NH3 L NH3

3

28.0

What if the problem is NOT at STP?

1. You will need to use PV = nRT

Gas Stoichiometry Example on HO

How many liters of oxygen gas, at 1.00 atm and 25 oC, can be collected from the complete decomposition of 10.5 grams of potassium chlorate?

2 KClO3(s) 2 KCl(s) + 3 O2(g)

10.5 g KClO3 1 mol KClO3

122.55 g KClO3

3 mol O2

2 mol KClO3

0.13 mol O2

Gas Stoichiometry Example on HO

How many liters of oxygen gas, at 1.00 atm and 25 oC, can be collected from the complete decomposition of 10.5 grams of potassium chlorate?

2 KClO3(s) 2 KCl(s) + 3 O2(g)

3.2 L O2

(1.0 atm)(V) (0.08206 atm*L/mol*K) (298 K)(0.13 mol)

Gas Laws: Dalton, Density and Gas Stoichiometry

At the conclusion of our time together, you should be able

to:

1. Explain Dalton’s Law and use it to solve a problem.

2. Use the Ideal Gas Law to solve a gas density problem.

3. Use the Ideal Gas Law to solve a gas stoichiometry problem.

GAS DENSITYGAS DENSITY

High density

Lower density

22.4 L of ANY gas AT STP = 1 mole

Gas Density

molar mass

molar volume

massDensity

volume

… so at STP…

molar mass

22.4 LDensity

Density and the Ideal Gas Law

Combining the formula for density with the Ideal Gas law, substituting and rearranging algebraically:

MPD

RT

M = Molar Mass

P = Pressure

R = Gas Constant

T = Temperature in Kelvins

Gas Stoichiometry #4

nRT

VP

How many liters of oxygen gas, at 37.0C and 0.930 atmospheres, can be collected from the complete decomposition of 50.0 grams of potassium chlorate?

2 KClO3(s) 2 KCl(s) + 3 O2(g)

= “n” mol O2

50.0 g KClO3 1 mol KClO3

122.55 g KClO3

3 mol O2

2 mol KClO3 = 0.612 mol O2

L atm(0.612mol)(0.0821 )(310K)

mol K0.930atm

= 16.7 L

Try this one!

How many L of O2 are needed to react 28.0 g NH3 at 24°C and 0.950 atm?

4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g)