The document discusses key concepts in stoichiometry including: - Stoichiometry deals with the relative quantities of reactants and products in chemical reactions. - Chemical reactions proceed according to mole ratios derived from balanced chemical equations. - There are specific steps to solve mole-to-mole, mole-to-mass, and mass-to-mass stoichiometry problems. - Limiting reactants determine the amount of product formed in a reaction. Excess reactants remain after the reaction completes. - Percent yield calculations compare the actual and theoretical yields of a chemical reaction.

1. Shane Izzy S. Labial
Kent B. Bulawin
BSECE/BSEE 1 - STEM
Chemistry for Engineers

2. • Defining Stoichiometry
• Stoichiometric Calculations
• Limiting Reactants
• Percent Yield

3. A branch of chemistry that deals with
the relative quantities of reactants
and products in chemical quantities.
Stoikhein - element | Metron - measure
"THE MEASURE OF ELEMENTS"

4. DEFINING STOICHIOMETRY
A
B
C The mass of reactants
equals the mass of the
products.
Stoichiometry is based on the
law of conservation of mass.
Chemical reactions stop
when one of the reactants
is used up.

5. Relationships Derived from a Balanced Chemical
Equation
4Fe(s)
Iron
4 atoms Fe
4 mol Fe
223.4 g Fe
3O (g)
2
Oxygen
2
3 molecules O
2
3 mol
O
2
96.00 g O
2Fe O (s)
2 3
Iron (III) Oxide
2 Formula Units Fe O
2 3
2 mol Fe O
2 3
319.4 g Fe O
2 3
319.4 g reactants 319.4 g products
+
+
+
+
+
→
→
→
→
→
→

6. A ratio between the numbers of molecules of
any two substances in a balanced equation.
The number of mole ratios that can be written
for any equation is (n) (n-1) where n is the
number of species in the chemical reaction.

7. A. 2 mol Al : 3 mol Br
B. 3 mol Br : 2 mol Al
C. 2 mol AlBr : 1 mol Br
D. 2 mol Br : 2 mol Al
Which of the following is the correct
mole ratio for the following equation?
2Al(s) + 3Br (l) → 2ABr (s)
2 3
2
3
2

8. B. 3 mol Br : 2 mol Al
2

9. • List the sequence of the steps used in
solving the stoichiometric problems.
• Solve the stoichiometric problems.

10. STOICHIOMETRY CALCULATIONS
A All stoichiometric
calculations begin with a
balanced chemical reaction.

11. mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems
• Write a balanced chemical equation for the reaction.
• Determine where to start your calculations by noting the
unit of the given substance.
• If the mass (grams) of the given
substance is the starting unit,
you must convert to moles.

12. mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems
• If the amount (moles) of the given substance is the
starting unit, convert moles of the given substance
to moles of the unknown.
3. The end point of the calculation
depends on the desired unit of the
unknown substance.

13. mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems
• If the answer is in moles, you are finished.
• If the answer is in grams, convert the moles of
unknown to grams of unknown using the molar
mass as the conversion factor.

14. The carbon dioxide exhaled by
astronauts can be removed from a
spacecraft by reacting with lithium
hydroxide as follows:
CO + LiOH → Li CO
2(g) (s) 2 3(s)
An average person exhales about 20
moles of CO per day. How many moles
of LiOH would be requires to maintain 2
astronauts in a spacecraft for 3 days?

15. • Balance the equation
CO → 2LiOH → Li CO + H O
2. Determine the moles given
20 moles per person, 2 people
= 40 moles x 3 days
= 120 moles of CO
3. Convert moles of the given
substance to molecules of the
unknown
2 3 2
120 mol CO x 2 mol/1 mol
= 240 moles of LiOH
2

16. • Identify the limiting reactant in a chemical
reaction.
• Identify the excess reactant and calculate
the amount remaining after the reaction is
complete.
• Calculate the mass of a product when the
amounts of more than one reactant is given.

17. Reactions proceed until one of the
reactions is used up and one is left in
excess.

18. Limits the extent of the
reaction and, thereby,
determines the amount of
product formed.
All the leftover, unused
reactants.

19. Determining the limiting reactant is important because the
amount of the product formed depends on this reactant.

20. If 200.0g of Sulfur reacts with 100.0g of Chlorine, what mass
of disulfur dichloride is produced?
• Determine the moles of the reactants
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

21. 2. Determine whether the 2 reactants are in the correct mole
ratio, as given in the balanced chemical reaction.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

22. Only 1.808 mol of Chlorine is available for every 1 mol Sulfur,
instead of 4 mol of Chlorine required by the balanced
chemical equation, thus, Chlorine is the limiting reactant.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

23. 3. Calculate the amount of product formed.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

24. Now that you have determined the limiting reactant and the
amount of product formed, what about the excess reactant
Sulfur? How much of it reacted?
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

25. • Make a mole-to-mass calculation to determine the mass
of Sulfur needed to react completely with 1.410 mol of
Chlorine.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

26. 2. Obtain the mass of Sulfur needed.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2

27. 3. Knowing that 200.0g of Sulfur is available and only 90.42
is needed, you can calculate the amount of Sulfur left
unreacted when the reaction ends.
S (I) + 4Cl (g) → 4S Cl (I)
8 2 2 2
• Using an excess reactant can speed up
the reaction and drive it to completion.

28. • Calculate the theoretical yield of a
chemical reaction from data.
• Determine the percent yield for a
chemical reaction.

29. Theoretical Yield is the maximum amount of
product that can be produced from a given
amount of reactant.
Actual Yield is the amount of product actually
produced when the chemical reaction is
carried out in an experiment.

30. Percent Yield is the ratio of the actual yield
expressed as a percent. It is important in the
cost effectiveness of many industrial
manufacturing processes.

31. • Laboratory reactions do not always
produce the calculated amount of
products.
• Reactants stick to containers.
• Competing reactions form other
products.

32. The amount of product that can be
produced from a given amount of
reactants based on the
stoichiometric calculations is:
A. Actual Yield
B. Percent Yield
C. Theoretical Yield
D. Stoichiometric Yield
If the theoretical yield of a
chemical reaction that began with
50.0g of reactant is 25.0g of
product. What is the percent yield
if the actual yield is 22.0g of
product?
A. 88%
B. 44%
C. 50%
D. 97%

33. C. Theoretical Yield
A. 88%

34. We hope you learned something new.