Quantities in Chemical Reactions

STOICHIOMETRY PROBLEMS

Section 5.4

What is Stoichiometry?• The study of quantitative relationships

within chemical reactions

• A balanced equation is the key to stoichiometry!

• Tools you’ll need for this chapter:– Writing proper formulas and balanced equations– Finding molar mass– Converting from mass to moles and vice versa

Balanced Reaction Equations and the Mole Ratio

• Consider this balanced reaction equation:

4 Al(s) + 3 O2(g) → 2 Al2O3(s)

The coefficients of this reaction represent:

- the number of reacting PARTICLES or

- the number of reacting MOLES

These numbers are FIXED, the ratio of reacting substances NEVER changes.

Stoichiometry Problems• There are three types of stoichiometry

problems we will encounter:– Mole-Mole problems (1 conversion factor)– Mass-Mole problems (2 conversion factors)– Mass-Mass problems (3 conversion factors)

given required

• Step 1: Write a BALANCED EQUATION

• Step 2: Determine the mole ratio from the coefficients in the equation.– Mole ratio = moles of required substance

moles of given substance

• Step 3: Multiply the amount of moles of the given substance by the mole ratio

Mole-Mole Problems

Mole-Mole ProblemsExample:

2 H2 + O22 H2O

How many moles of water can be formed from 0.5 mol H2? 0.5 mol H2 x

2 mol H2

2 mol H2O 0.5 mol H2O=

Mole-Mole PracticeCuSO4 Al Al2(SO4)3 Cu3 2 3+ +

Mole ratio

0.5 mol Al 3 mol CuSO4

2 mol Al=x 0.8 mol CuSO4

How many moles of copper(II) sulfate will react with 0.5 moles of aluminum?

Mass-Mole ProblemsExample:

2 H2 + O22 H2O

How many moles of water can be formed from 48.0 g O2?

Mass48.0g

Mole RatioMoles Moles?

Mass

2 H2 + O22 H2O

Setting up the given information

Mass-Mole Problems• Step 1: Write a BALANCED EQUATION.

• Step 2: Convert the mass of your given substance to moles using molar mass.

• Step 3: Determine the moles of your required substance using the mole ratio.

Mass48.0g

Mole RatioMoles Moles?

Mass

2 H2 + O22 H2O

Setting up the given informationStep 1

Step 2:M = 32.00g/mol

Step 3

Mass-Mole ProblemsExample:

2 H2 + O22 H2O

How many moles of water can be formed from 48.0 g O2?

48.0 g O2 x1 mol O2

2 mol H2O = 3.00 mol H2O

32.00 g O2

1 mol O2 x

Mass-Mole Practice

CuSO4 Al Al2(SO4)3 Cu3 2 3+ +

13.5 g Al 1 mol Al2(SO4)3

2 mol Al=x 0.250 mol

Al2(SO4)3

Mole ratio

1 mol Al

26.98 g Alx

How many moles of aluminum sulphate can be produced from13.5 g of aluminum?

Mass-Mole PracticeCa AlCl3 CaCl2 Al3 2 2+ +3

How many moles of calcium chloride will be produced if 5.7gof calcium is used up in the reaction?

Mass-Mole Practice

5.7 g Ca 3 mol CaCl2

3 mol Ca=x 0.14 mol CaCl2

Ca AlCl3 CaCl2 Al3 2 2+ +

x1 mol Ca

40.08 g Ca

3

How many moles of calcium chloride will be produced if 5.7gof calcium is used up in the reaction?

Mass-Mass ProblemsExample:

2 H2 + O22 H2O

How many grams of water can be formed from 48.0 g O2?

Mass48.0g

Mole RatioMoles Moles

Mass?

2 H2 + O22 H2O

Setting up the given informationStep 1

Step 2:M = 32.00g/mol

Step 3

Step 4:M = 18.02g/mol

Mass-Mass ProblemsExample:

2 H2 + O22 H2O

How many grams of water can be formed from 48.0 g O2?

48.0 g O2 x1 mol O2

2 mol H2O =32.00 g O2

1 mol O2 x x18.02 g H2O

1 mol H2O54.1 g H2O

Mass-Mass PracticeCa AlCl3 CaCl2 Al3 2 2+ +3

How much aluminum is produced (in grams) when 1.9g of calcium reacts with aluminum chloride?

Mass-Mass PracticeCa AlCl3 CaCl2 Al3 2 2+ +3

1.9 g Ca 2 mol Al

3 mol Ca=x

0.85 g Al

1 mol Ca x40.08 g Ca

x 26.98 g Al

1 mol Al

How much aluminum is produced (in grams) when 1.9g of calcium reacts with aluminum chloride?