Not so long ago, in a chemistry lab far far away…

May the FORCE/area be with you

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.

When you know the guy has finally had enough!!!

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 Page 41:1

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

28.00

How to Report Computer Problems:

What if the problem is NOT at STP?

1. You will need to use PV = nRT

Gas Stoichiometry Example Page x:1

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 Page x:1

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: Gas Stoichiometry

Let’s see if you can:

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

Now we’re in big Do-Do

Gas Stoichiometry Page x:2

1 P4 (s) + 6 H2 (g) 4 PH3 (g)

2.51 g P4 1 mol P4

123.88 g P4

6 mol H2

1 mol P4

0.122 mol H2

3.0 L H2

(0.991 atm)(V) (0.08206 atm*L/mol*K) (298 K)(0.122 mol)

Gas Stoichiometry Page x:2

1 P4 (s) + 6 H2 (g) 4 PH3

(g)

Quicklime Example Page x:3

1 CaCO3 (s) 1 CaO (s) + 1 CO2

(g)

152 g CaCO3

100.09 g 1 mol CaCO3

1 mol CO21 mol CaCO3

= 34.0 L CO2 at STP

1 mol CO2

22.4 L CO2

Pass the Clicker!!!

Zinc will react with hydrochloric acid. What are the 2 products for this reaction?

1. ZnCl + H

2. ZnCl + H2

3. Zn2Cl + H2

4. ZnCl2 + H2

5. Not listed

Zinc will react with hydrochloric acid. What kind of reaction is this?

1. DD2. SD3. Synthesis4. Decomposition5. Not listed

Zinc will react with hydrochloric acid. This reaction will form ZnCl2 + H2. What are the 4 coefficients for the balanced chemical equation?

1. 1,2,1,22. 2,1,2,13. 1,1,1,14. 2,2,1,25. Not listed

Zinc will react with hydrochloric acid. The hydrogen gas is collected through water at 30.0oC and 782 mm Hg. The vapor pressure of water at 30.0oC is 32.0 mm Hg. What is the partial pressure of H2?

1. 250 atm2. 314 atm3. 0.329 atm4. 0.987 atm5. Not listed

Zinc ( 65.39 g/mole) will react with hydrochloric acid. Determine the grams of zinc that must be reacted to produce this quantity of hydrogen if the volume is 142 mL . (P = 0.987 atm, T = 30.0oC)

1. 0.112 g2. 1.18 g3. 628 g4. 0.000 628 g5. 0.369 g

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)