CA StandardsStd. 3e: Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.

What is Stoichiometry?

The study of quantities of materials consumed and produced in chemical reactions.

How Are Stoich Problems Different?

• Includes a balanced equation and molar conversions.

• Coefficient of equation shows molar relationship (Mole ratio) of reactants and products.

Ex: 2H2 + O2 2H2O

2 mol H2 + 1 mol O2 2 mol H2O

Ex: Mole Ratio of H2: H2O 2 mol H2

2 mol H2O

Calculating Masses of Reactants and Products

1. Check if equation is balanced.

2. Convert mass(g) or volume(L) to moles, if necessary.

3. Set up mole ratios.

4. Use mole ratios to calculate moles of desired substituent.

5. Convert moles to mass or volume, if necessary.

1. Check if equation is balanced.

2. Convert mass(g) or volume(L) to moles, if necessary.

3. Set up mole ratios.

4. Use mole ratios to calculate moles of desired substituent.

5. Convert moles to mass or volume, if necessary.

Stoich problem Type #1Ex 1: How many moles of NH3 can be produced when 4 moles of N2 is reacted with excess H2?

N2 + 3H2 2NH3

4 mol N2

= 8 mol NH3

2 mol NH3

1 mol N2

Ex 2:

2N2 + O2 2N2O

How many moles of N2 must be reacted with excess O2 to produce 10 moles of N2O?

10 mol N2O

2 mol N2

2 mol N2O

= 10 mol N2

Grams of Given to Grams of Unkown Roadmap

MEMORIZE!!!

(Mole Ratio)

g GIVEN mol GIVEN mol UnKnown g UNKNOWN

mol GIVEN

Stoich Problem Type#2 Ex 3: 46 grams of Sodium (Na) reacts with an excess Chlorine (Cl). How many grams of Sodium Chloride (NaCl) are formed?

2Na + Cl2 2NaCl

=46 g Na

116 g NaCl

1 mol Na

23 g Na 2 mol Na

2 mol NaCl

1 mol NaCl

58 g NaCl

• Ex 4: How many grams of water can be prepared from 8 grams of hydrogen at standard conditions?

2 H2 (g) + O2(g) → 2 H2O

8 g H2

= 72 g H2O

1 mol H2 2 g H2

2 mol H2O

2 mol H2 1 mol H2O

18 g H2O

Gas Stoichiometry 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 3 liters H2 + 1 liter N2 2 liters NH3

Gas StoichiometryEx 5: How many liters of NH3 can be produced when 12 liters of H2 react with an excess of nitrogen?

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

12 L H2

L H2

= L NH3 L NH3

3

28.0

Ex 6: How many liters of oxygen are required to react completely with 22.4 liters of carbon monoxide, CO, at standard conditions?

2 CO (g) + O2(g) → 2 CO2 (g)

22.4 L CO

L CO = L O2

L O2

2

111.2

END OF UNIT 3: Woo Hoo!

Everyday STOICHS’mores:

G2 + C + M G2CM

+ +

How many S’mores can I make with 5 Graham crackers, 3 marshmallows and 1 Chocolate?