Quantities in Chemical Reactions STOICHIOMETRY PROBLEMS

1
Quantities in Chemical Reactions STOICHIOMETRY
PROBLEMS

• Section 5.4

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What is Stoichiometry?

• The study of quantitative relationships within
  chemical reactions
• A balanced equation is the key to stoichiometry!
• Tools youll need for this chapter
• Writing proper formulas and balanced equations
• Finding molar mass
• Converting from mass to moles and vice versa

3
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.

4
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
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Mole-Mole Problems

• 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

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Mole-Mole Problems
Example
2 H2O
2 H2 O2
How many moles of water can be formed from 0.5
mol H2?
2 mol H2O
0.5 mol H2
0.5 mol H2O
x

2 mol H2
7
Mole-Mole Practice
CuSO4
Al
Al2(SO4)3
Cu


How many moles of copper(II) sulfate will react
with 0.5 moles of aluminum?
8
Mass-Mole Problems
Example
2 H2O
2 H2 O2
How many moles of water can be formed from 48.0 g
O2?
9
Setting up the given information
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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.

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Setting up the given information
Step 1
Step 2 M 32.00g/mol
Step 3
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Mass-Mole Problems
Example
2 H2O
2 H2 O2
How many moles of water can be formed from 48.0 g
O2?
2 mol H2O
1 mol O2
48.0 g O2
3.00 mol H2O
x

x
1 mol O2
32.00 g O2
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Mass-Mole Practice
How many moles of aluminum sulphate can be
produced from 13.5 g of aluminum?
Mole ratio
1 mol Al2(SO4)3
1 mol Al
13.5 g Al
x
0.250 mol Al2(SO4)3
x

2 mol Al
26.98 g Al
14
Mass-Mole Practice
Ca
AlCl3
CaCl2
Al


3
How many moles of calcium chloride will be
produced if 5.7g of calcium is used up in the
reaction?
15
Mass-Mole Practice
Ca
AlCl3
CaCl2
Al


3
How many moles of calcium chloride will be
produced if 5.7g of calcium is used up in the
reaction?
3 mol CaCl2
1 mol Ca
5.7 g Ca
x
0.14 mol CaCl2
x

3 mol Ca
40.08 g Ca
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Mass-Mass Problems
Example
How many grams of water can be formed from 48.0 g
O2?
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Setting up the given information
Step 1
Step 2 M 32.00g/mol
Step 4 M 18.02g/mol
Step 3
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Mass-Mass Problems
Example
How many grams of water can be formed from 48.0 g
O2?
2 mol H2O
1 mol O2
18.02 g H2O
48.0 g O2
54.1 g H2O
x

x
x
1 mol O2
32.00 g O2
1 mol H2O
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Mass-Mass Practice
Ca
AlCl3
CaCl2
Al


3
How much aluminum is produced (in grams) when
1.9g of calcium reacts with aluminum chloride?
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Mass-Mass Practice
Ca
AlCl3
CaCl2
Al


3
How much aluminum is produced (in grams) when
1.9g of calcium reacts with aluminum chloride?