1. UNIT 9: STOICHIOMETRY

2. Section 1: What is Stoichiometry?
More than 3000 silk cocoons are needed to make just one kimono. Like silk manufacturers, chemists must know how much reactant
they need to make a certain
amount of product.
Determining the quantities
of reactants and products
in a reaction requires a
balanced chemical equation.

3. Using Balanced Chemical Equations
chemists use balanced chemical equations to calculate how much reactant is needed or product is formed in a reaction.
stoichiometry:
the calculation of quantities in chemical reactions.

4. Interpreting Chemical Equations
A balanced chemical equation can tell the amount of:
atoms, molecules, or moles;
and mass.
The most important info is the
mol-to-mol ratios

5. Interpreting Chemical Equations
Atoms
The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

6. Interpreting Chemical Equations
Molecules
The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

7. Interpreting Chemical Equations
Moles
The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?
# of molecules = # of moles

8. Interpreting Chemical Equations
Mass
The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

9. Interpreting Chemical Equations
Mass & Atoms
Mass and atoms are conserved in every chemical reaction

10. Atoms Mass Molecules Moles 12 12 164.18 g 164.18 g 5 4 5 4
Conceptual Problem 12.1
Atoms
Mass
Molecules
Moles 12 12 g g 5 4 5 4

11. Mole Ratios
A mole ratio is a ratio between the numbers of moles of any two substances in a balanced equation.
Mole ratios convert moles of one substance to moles of another substance.

12. Mol to Mol Ratios
2 H O2 → 2 H2O
2 mol H2 for every 1 mol O2

13. Mol to Mol Ratios
2 H O2 → 2 H2O
2 mol H2 for every 2 mol H2O

14. 2 H O2 → 2 H2O
There are 6 mol to mol ratios that can be written from this balanced equation:
2 mol H mol O mol H2O
1 mol O mol H mol H2
2 mol H mol O mol H2O
2 mol H2O mol H2O 1 mol O2
To determine the number of moles in a sample of a compound, first measure the mass of the sample. Then use the molar mass to calculate the number of moles in that mass. 14

15. Mg + 2 HCl → MgCl2 + H2 1 mol H2 1 mol Mg 4.0 mol Mg x = 4.0 mol H2
Mole to Mole Conversion
How many moles of hydrogen gas (H2) are produced from 4.0 mol Mg?
Mg HCl → MgCl2 + H2
1 mol H2
1 mol Mg
4.0 mol Mg x =
4.0 mol H2
mol ratio 15

16. Mg + 2 HCl → MgCl2 + H2 1 mol H2 2 mol HCl 4.0 mol HCl x = 2.0 mol H2
Mole to Mole Conversion
How many moles of hydrogen gas (H2) are produced from 4.0 mol HCl?
Mg HCl → MgCl2 + H2
1 mol H2
2 mol HCl
4.0 mol HCl x =
2.0 mol H2
mol ratio 16

17. Quick Quiz.
1. What is conserved in the reaction shown below?
H2(g) + Cl2(g)  2HCl(g)
only mass
only mass and atoms
only mass, atoms, and moles
mass, atoms, moles, and molecules

18. Quick Quiz.
2. What is the most important information from a chemical equation?
states of matter
moles of products
mol-to-mol ratios of reactants and products
mass of reactants

19. C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g)
Quick Quiz!
3. How many moles of water are produced from burning 4.00 mol of ethanol (C2H5OH)?
C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g)
3.00 mol H2O
4.00 mol H2O
12.0 mol H2O
1.33 mol H2O