1. Chapter 12: Stoichiometry
The Arithmetic of Equations
Chemical Calculations

2. Learning Targets
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.
Show examples of both kinds of problems and have students talk about difference
Show example of mole mole
Try on own
Put in steps for mass to mass
Show example
Talk about what if starts at mass, stops at moles; or starts at moles, stop at mass

3. Chemical Equations
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

4. Chemical Equations N2 (g) + 3 H2 (g)  2 NH3 (g) Atoms:
2 atoms N + 6 atoms H  2 atoms N and 6 atoms of H
8 atoms  8 atoms
number and type of atoms don’t change
reactant atoms = product atoms
Number of molecules:
1(6.02 x 1023 molecules N2) + 3(6.02 x 1023 molecules H2)  2(6.02 x 1023 molecules NH3)
ratio is still 1:3:2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

5. Chemical Equations N2 (g) + 3 H2 (g)  2 NH3 (g) Moles:
1 mol N2 + 3 mol H2  2 mol NH3
ratio is still 1:3:2
Volume (assuming STP):
22.4 L + (3 x 22.4 L)  (2 x 22.4 L)
ratio still 1:3:2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

6. Chemical Equations N2 (g) + 3 H2 (g)  2 NH3 (g) Mass:
28.0 g N2 + (3 x 2.0 g H2)  (2 x 17.0 g NH3)
34.0 g  34.0 g
reactant mass = product mass
total mass doesn’t change
law of conservation of mass satisfied
ratio is NOT 1:3:2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

7. Example: Interpreting a Balanced Chemical Equation
Hydrogen sulfide, which smells like rotten eggs, is found in volcanic gases. The balanced equation for the burning of hydrogen sulfide is
2 H2S (g) + 3 O2 (g)  2 SO2 (g) + 2 H2O (g)
Interpret this equation in terms of:
Numbers of moelcules and moles
Masses of reactants and products
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

8. Answers: Interpreting a Balanced Chemical Equation
Numbers of representative particles and moles
2 molecules H2S + 3 molecules O2 
2 molecules SO2 + 2 molecules H2O
2 mol H2S + 3 mol O2 
2 mol SO2 + 2 mol H2O
Masses of reactants and products
(2 mol x 34.1 g/mol) + (3 mol x 32.0 g/mol) 
(2 mol x 64.1 g/mol) + (2 mol x 18.0 g/mol)
68.2 g H2S g O2  g SO g H2O
164.2 g = g
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

9. Try on your own 2 H2 (g) + O2 (g)  2 H2O (g)
Interpret the equation for the formation of water from its elements in terms of numbers of molecules and moles, and volumes of gases at STP.
2 H2 (g) + O2 (g)  2 H2O (g)
2 molecules H2 + 1 molecule O2 
2 molecules H2O
2 mol H2 + 1 mol O2  2 mol H2O
44.8 L H L O2  44.8 L H2O
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

10. Mole Ratios
used to convert between a given number of moles of a reactant or product to moles of a different reactant or product
derived from coefficients of balanced chemical equation
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

11. Mole Ratios - Example
How many moles of NH3 are produced when 0.60 mol of nitrogen reacts with hydrogen?
N2 (g) + 3 H2 (g)  2 NH3 (g)
1.2 mol NH3
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

12. Mole Ratios - Example (work)
How many moles of NH3 are produced when 0.60 mol of nitrogen reacts with hydrogen?
N2 (g) + 3 H2 (g)  2 NH3 (g)
1.2 mol NH3
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

13. Mole Ratios - Try on your own
How many moles of aluminum are needed to form 3.7 mol Al2O3 according to the following equation?
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
7.4 mol Al
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

14. Mole Ratios - Try on your own (work)
How many moles of aluminum are needed to form 3.7 mol Al2O3 according to the following equation?
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
7.4 mol NH3
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

15. Mass-Mass Calculations
Can’t measure lab materials in moles so have to utilize mass to mol conversion
Mole ratio is basis for conversion
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

16. Mass-Mass Calculations - Example
Ammonia (NH3) clouds are present around some planets, as in Figure Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. The balanced equation is
N2 (g) + 3 H2 (g)  NH3 (g)
30.4 g NH3
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

17. Mass-Mass Calculations - Example (work)
Ammonia (NH3) clouds are present around some planets, as in Figure Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. The balanced equation is
N2 (g) + 3 H2 (g)  2 NH3 (g)
30.4 g NH3
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

18. Mass Calculations - Try on your own
Acetylene gas (C2H2) is produced by adding water to calcium carbide (CaC2).
CaC2 (s) + 2 H2O (l)  C2H2 (g) + Ca(OH) 2 (aq)
How many grams of acetylene are produced by adding water to 5.00 g CaC2?
2.03 g C2H2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

19. Mass Calculations - Try on your own (work)
Acetylene gas (C2H2) is produced by adding water to calcium carbide (CaC2).
CaC2 (s) + 2 H2O (l)  C2H2 (g) + Ca(OH) 2 (aq)
How many grams of acetylene are produced by adding water to 5.00 g CaC2?
2.03 g C2H2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

20. Calculating Molecules of a Product - Example
How many molecules of oxygen are produced when 29.2 g of water is decomposed by electrolysis according to this balanced equation?
2 H2O (l) 
2 H2 (g) + O2 (g)
4.88 x 1023 molecules O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

21. Calculating Molecules of a Product – Example (work)
How many molecules of oxygen are produced when 29.2 g of water is decomposed by electrolysis according to this balanced equation?
2 H2O (l)  2 H2 (g) + O2 (g)
4.88 x 1023 molecules O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

22. Calculating Molecules of a Product – Try on your own
How many molecules of oxygen are produced by the decomposition of 6.54 g of potassium chlorate (KClO3)?
2 KClO3 (s) 
2 KCl (s) + 3 O2 (g)
4.82 x 1022 molecules O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

23. Calculating Molecules of a Product – Try on your own (work)
How many molecules of oxygen are produced by the decomposition of 6.54 g of potassium chlorate (KClO3)?
2 KClO3 (s)  2 KCl (s) + 3 O2 (g)
4.82 x 1022 molecules O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

24. Volume-Volume Stoichiometric Calculations - Example
Nitrogen monoxide and oxygen gas combine to form the brown gas nitrogen dioxide, which contributes to photochemical smog. How many liters of nitrogen dioxide are produced when 34 L of oxygen react with an excess of nitrogen monoxide? Assume conditions are at STP.
2 NO (g) + O2 (g)  2 NO2 (g)
68 L of NO2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

25. Volume-Volume Stoichiometric Calculations – Example (work)
Nitrogen monoxide and oxygen gas combine to form the brown gas nitrogen dioxide, which contributes to photochemical smog. How many liters of nitrogen dioxide are produced when 34 L of oxygen react with an excess of nitrogen monoxide? Assume conditions are at STP.
2 NO (g) + O2 (g)  2 NO2 (g)
68 L of NO2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

26. Volume-Volume Stoichiometric Calculations – Try on your own
The equation for the combustion of carbon monoxide is
2 CO (g) + O2 (g)  2 CO2 (g)
How many liters of oxygen are required to burn 3.86 L of carbon monoxide? Assume conditions are at STP.
1.93 L O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

27. Volume-Volume Stoichiometric Calculations – Try on your own (work)
The equation for the combustion of carbon monoxide is
2 CO (g) + O2 (g)  2 CO2 (g)
How many liters of oxygen are required to burn 3.86 L of carbon monoxide? Assume conditions are at STP.
1.93 L O2
You will perform calculations converting between grams, moles, atoms, molecules, or the volume of a substance.
You will use stoichiometric calculations (mole ratios) to determine the grams, moles, or volume of a substance in a balanced chemical equation.

28. Quiz
How many moles of oxygen (O2) are needed to make 14.0 moles of lead (II) oxide (PbO)?
2 Pb (s) + O2 (g)  2 PbO (s)
What mass of boron trifluoride (BF3) can be made from 30.0 g of fluorine (F2)?
2 B (s) + 3 F2 (g)  2 BF3 (g)
Iron turns to rust by the reaction
4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s)
Calculate the mass of iron needed to fully react with 18.0 moles of oxygen gas.

29. Homework
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You will learn to use a balanced equation to carry out mole and mass calculations.