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 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?
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?
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