- Stoichiometry is the branch of chemistry that deals with quantities of substances in chemical reactions. - Balanced chemical equations show the proportions of reactants and products using coefficients, which represent numbers of particles or moles. - Mole ratios obtained from coefficients in balanced equations allow conversions between known and unknown amounts of substances in moles or grams. - Stoichiometry problems typically involve a multi-step process of converting between grams and moles using molar masses and mole ratios to solve for unknown amounts.

1. Balanced Reactions
• A balanced chemical reaction can show how much of a
certain product is made, given a certain amount of
reactant, since coefficients represent number of
particles.
• Coefficients in a balanced equation represent the
numbers of particles for each substance in a reaction, but
in a practical sense, they represent moles.

2. 2H2 + 1O2  2H2O
_NH3 + _HCl  _NH4Cl

3. Activity!
WEIGHT OFTHE
CROWN

4. Procedure
• The class will be divided into 4 groups
• TheTeacher will post an unbalance chemical equations on
the board/monitor
• The groups will try to solve the equations by choosing the
correct numbers represented by the crowns.
• After determining which crown will be used to solve the
equation members of the group will wear the crown and
stand at the right spot/place in the equation to balance it.

5. Stoichiometry

6. • The branch of Chemistry that deals with quantities of
substances in chemical reactions is known as
stoichiometry.

7. Balanced Equations Show
Proportions
• When performing chemical reactions, it is necessary to
find out either how much of the reactants are needed in
relation to each other, how much of the products can be
obtained from a known amount of reactants, or how
much of the reactants are needed for a desired amount of
product. A balanced reaction shows the proportions of all
reactants and products in relation to each other.

8. Mole Ratio
• In stoichiometry problems, the mole ratio (obtained from
the coefficients in a balanced equation) lets you convert
from moles of a known substance to moles of an
unknown substance.

9. Calculating the Mole Ratio
1. The mole ratio is obtained by first balancing the
equation.
2. Using coefficients from the balanced equation, set up
the mole ratio with the known substance on the bottom
(mole units with chemical, and the unknown substance
on top (mole units and chemical)).
Mole numbers are from the coefficients.

10. Mole Ratio is a Conversion Factor
• The Mole ratio is setup in fraction form just like any other
conversion factor, except now it converts given chemicals
to unknown or asked for chemicals.

11. Sample Problem
• For the balanced equation:
1N2 + 3H2  2NH3
How many moles of hydrogen are needed to prepare 312 moles
ammonia?
NH3 = ammonia

12. 312 mol NH3 x 3 molH2 = 468 mol H2
2 mol NH3

13. Steps for Stoichiometry
• 1. Balance equation
• 2. Write what is given (#, unit, and chemical)
• 3. Convert to moles of the chemical given if not already in
moles
• 4. Calculate mole ratio and setup as a conversion factor to
convert to unknown chemical
• 5. Convert out of moles if problem asks for unknown chemical
in different units.

14. Stoichiometry
Consider the chemical equation:
4NH3 + 5O2  6H2O + 4NO
“stochio” = Greek for element
“metry” = measurement
Stoichiometry is about measuring the amounts of
elements and compounds involved in a reaction.

15. Stoichiometry
Recall that Chemical formulas are balanced with coefficients
4NH3 + 5O2  6H2O + 4NO
4 X NH3 = 4 nitrogen + 12 hydrogen
5 X O2 = 10 oxygen
6 X H2O = 12 hydrogen + 6 oxygen
4 X NO = 4 nitrogen + 4 oxygen

16. Stoichiometry
With Stoichiometry we find out that
Coefficients like
4 : 5 : 6 : 4
4NH3 + 5O2  6H2O + 4NO
convey the ratio of substances need for a
reaction to occur, in terms of moles ( mole
ratio)
4 : 5 : 6 : 4

17. Stoichiometry
4NH3 + 5O2  6H2O + 4NO
4 : 5 : 6 : 4
Can mean either:
4 molecules of NH3 react with 5 molecules of O2
to produce 6 molecules of H2O and 4 molecules of NO
OR
4 moles of NH3 react with 5 moles of O2
to produce 6 moles of H2O and 4 moles of NO

18. Stoichiometry Question (1)
4NH3 + 5O2  6H2O + 4NO
How many moles of H2O are produced if 2.00 moles of O2 are used?
2.00 mol O2 2.40 mol H2O
=
Notice that a correctly balanced equation is
essential to get the right answer
6 mol H2O
5 mol O2

19. 4 mol NO
6 mol H2O
Stoichiometry Question (2)
4 NH3 + 5 O2  6 H2O + 4 NO
How many moles of NO are produced in the reaction if 15 mol of H2O are also
produced?
15 mol H2O 10. mol NO
=

20. 18.02 g H2O
1 mol H2O
6 mol H2O
4 mol NH3
Stoichiometry Question (3)
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of H2O are produced if 2.2 mol of NH3 are combined with
excess oxygen?
2.2 mol NH3
59 g
H2O
=

21. 5 mol O2
6 mol H2O
32 g O2
1 mol O2
Stoichiometry Question (4)
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of O2 are required to produce 0.3 mol of H2O?
0.3 mol H2O 8 g O2
=

22. Stoichiometry Question (5)
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of NO is produced if 12 g of O2 is combined with excess
ammonia?
4 mol NO
5 mol O2
x
12 g O2
9.0 g NO
=
30.01 g NO
1 mol NO
x
1 mol O2
32 g O2
x

23. Moving along the stoichiometry path
We always use the same type of information to make the jumps between
steps:
grams (x)  moles (x)  moles (y)  grams (y)
Molar mass of x Molar mass of y
Mole ratio from
balanced equation

24. Many stoichiometry problems follow a pattern:
grams(x)  moles(x)  moles(y)  grams(y)
Converting grams to grams
We can start anywhere along this path
depending on the question we want to answer
Notice that we cannot directly convert from
grams of one compound to grams of another.
Instead we have to go through moles.

25. Have we learned it yet?
Try these on your own - 4 NH3 + 5 O2  6 H2O + 4 NO
a) How many moles of H2O can be made using 1.6 mol NH3?
b) what mass of NH3 is needed to make 0.75 mol NO?
c) how many grams of NO can be made from 47 g of NH3?

26. Answers
4 NH3 + 5 O2  6 H2O + 4 NO
a)
b)
c)
6 mol H2O
4 mol NH3
x
1.6 mol NH3
2.4 mol
H2O
=
4 mol NH3
4 mol NO
x
0.75 mol NO 13 g
NH3
=
17.04 g NH3
1 mol NH3
x
4 mol NO
4 mol NH3
x
47 g NH3
83 g NO
=
30.01 g NO
1 mol NO
x
1 mol NH3
17.04gNH3
x

27. Assessment:
Answer the following
Stoichiometric Problems.

28. 2 KClO3 → 2 KCl + 3 O2
How many moles of O2 will be formed from 1.65 moles of KClO3?
How many moles of KClO3 are needed to make 3.50 moles of
KCl?
How many moles of KCl will be formed from 2.73 moles of KClO3?
How many grams of O2 are produced when 25 grams of KClO3 is
reacted?
How many grams of O2 are produced when 35 grams of KCl is
reacted?

29. 2 C4H10 + 13 O2 → 8 CO2 + 10 H2O
How many grams of H2O are produced when
5.38g of O2 is reacted?
How many grams of O2 are needed to react
with of 100 grams of butane(C4H10)?
How many grams of CO2 are produced from the
combustion of 100 grams of butane?
How many moles of C4H10 are needed to
produced 10 moles of CO2?

30. For additional Stoichiometry
activities you can go to this site:
https://teachchemistry.org/classroom-
resources/stoichiometry-unit-plan