GENERAL CHEMISTRY
Calculations Based on Chemical Equations
Study Sheet for Self-Paced Study
Sheet No. 4
OBJECTIVES:
1. Given a balanced chemical equation you should be able to determine:
a. The number of moles of any specified product that will be produced by the reaction of a
given number of moles of reactant.
b. Determine the number of moles of reactant necessary to produce a given number of moles of
product.
2. Given the weight of reactant in a reaction calculate the weight of product. Or given product weight
calculate the weight of reactant necessary to give this amount of product.
3. Calculate percentage yield of a reaction or given the percent yield calculate the weight of products
that can be expected.
4. Be able to balance any chemical equation given all the reactants and all of the products.
a. Calculation of number of moles of product.
1. Consider the following reaction
CaCO3 + 2HCl
CaCl2 + CO2 + H2O
If we have 1 mole CaCO3 to start with, then we will produce
a. 1 mole CaCl2
b. 1 mole CO2
c. 1 mole H2O
NOTE: 2 moles HCl would be required to completely react with the CaCO 3.
2. Consider a second example
2KClO3
2KCl + 3O2
2 moles KClO3 would give
a. 2 moles KCl
b. 3 moles O2
1 mole KClO3 would give
a. _____ moles KCl
b. _____ moles O2
To answer this last question we need to make the conversion
moles KClO3
moles O2
(1)
From the balanced equation we know that
2 moles KClO3 = 3 moles O2
(2)
? moles O2 = 1 mole KClO3
(3)
? moles O2 = 1 mole KClO3 
QUESTION: For the reaction H2 + Cl2
3 moles O 2
2 moles KClO 3
(4)
2HCl
a. How many moles of HCl would be produced by the reaction of 2 moles of H 2 with 2 moles of
Cl2?
b. How many moles of HCl would be produced by the reaction of 2 moles of H 2 with 1 mole Cl2?
c. How many moles of H2 would be required to produce 0.10 mole HCl?
B.
Calculation of mass of product
1.
What is the weight of 2 mole NaCl?
The molecular weight of NaCl is 58.5 g/mole.
58.5 g
1 mole
= 117.0 grams NaCl
? g NaCl = 2 moles NaCl 
2.
(5)
(6)
Now consider the reaction
2Na + Cl2
2NaCl
What weight of NaCl will be produced by the reaction of 2 moles of Cl 2?
2 moles NaCl
1 mole Cl 2
= 4 moles NaCl
1) ? moles NaCl = 2 moles Cl2 
(7)
2) ? g NaCl = 4 moles NaCl 
58.5 g
1 mole
(8)
3) ? g NaCl = 4 moles Cl2 
2 moles NaCl 58.5 g NaCl

1 mole Cl 2
1 mole NaCl
(9)
3.
Consider the reaction
NH4NO3
N2O + 2H2O
How many grams of N2O can be produced by the reaction of 0.5 mole of NH 4NO3?
? g N2O = 0.5 mole NH4NO3 
1 mole N 2 O
44 g

1 mole NH 4 NO 3 1 mole N 2 O
(10)
= 22 g N2O
QUESTION 2: For the reaction
2AgNO3 + H2S
Ag2S + 2HNO3
Calculate
a. the number of moles HNO3 produced by the reaction of 5 moles of AgNO3.
b. the number of grams of HNO produced by the 1.4 moles H 2S.
c. the number of grams of H2S necessary to produce 2 moles Ag2 S.
C. Calculation of percent yield.
1.
Definition: The percentage yield of a chemical reaction is the ratio.
Actual weight of product
 100
maximum possible weight of product
2.
Consider the reaction of Na and Cl2 discussed in part 2 of this section. If 116.8 grams of
NaCl is actually produced in the reaction of 2 moles of Cl2, what is the percentage yield
of the reaction.
actual weight of product = 116.8 g
maximum possible weight = 4  58.4
= 253.6 g
% yield =
116.8
 100
233.6
% yield = 50%
(11)
(12)
Example 2:
In the production of N2O discussed in part 3 above, if 20 grams of N2O is produced by the
reaction of 0.5 mole NH4NO3, what is the percent yield?
20 g
 100
22 g
(13)
% yield = 90.9% yield
(14)
% yield =
QUESTION 3: For the reaction
Cu + Cl2
CuCl2
If 0.10 mole copper yields 10 grams CuCl2, what is the percent yield of the reaction.
D. Calculation of mass of product from mass of reactant
1. For the reaction
C4H10 + O2
2C4H10 + 13O2
CO2 + H2O
8CO2 + 10H2O
(15)
What weight of CO2 would be produced by the reaction of 10 grams of butane (C 4H10)?
? g CO2 = 10 g C4H10 
1 mole C 4 H 10
8 moles CO 2
44 g CO 2


58 g
2 moles C 4 H 10 1 mole CO 2
= 30.34 g CO2
(16)
(17)
2. For this same reaction what weight of O2 would be required to react with 10 g of C4H10?
? g CO2 = 10 g C4H10 
1 mole C 4 H 10
8 moles CO 2
32 g O 2


58 g
2 moles C 4 H 10 1 mole O 2
= 35.9 g O2
(18)
(19)
3. For the reaction
AgCl + 2NH3
Ag(NH3)2+ + Cl-
What weight of NH3 would be required to dissolve 1.43 g AgCl?
? g NH = 1.43 g AgCl 
= .34 g NH3
17 g NH 3
1 mole AgCl 2 moles NH 3


143 g AgCl
1 mole AgCl 1 mole NH 3
(20)
(21)
SELF-HELP TEST
1. During the process of photosynthesis plants produce glucose and oxygen from carbon dioxide and
water according to the (unbalanced) equation.
CO2 + H2O
C6H12O6 + O2
a. Balance the equation.
b. Calculate the mass of glucose, C6H12O6, produced by the reaction of 500 grams of CO 2 .
c. What weight of H2O would be required to react with 10 grams of CO2?
d. What weight of CO2 would be required to produce 44.8 liters of O 2 STP?
2. The fertilizer called superphosphate is made by adding sulfuric acid to phosphate rock, Ca 3(PO4)2, as
follows:
Ca3PO4)2 + 2H2SO4
Ca(H2PO4)2 + 2CaSO4
What weight of H2SO4 must be used to produce 1 kilogram of superphosphate, Ca(H2PO4)2?
3. Limestone and marble have the same chemical composition CaCO3. It was common practice in early
Christian communities to destroy statuary by converting it to lime for building purposes. The
reaction is:
CaCO
CaO + CO2
heat
a. What weight of lime, CaO would be produced by the reaction of 200 grams of CaCO 3?
b. If 100 grams CaO is produced from the 200 g CaCO 3, what is the percent yield of the
reaction?
ANSWERS TO QUESTIONS
Answers for questions for page 2.
1.
a. 4 moles HCl
b. 2 moles HCl (Be careful)
c. 0.05 mole H2
Answers to problems for page 3.
2. a. 5 moles HNO3
b. 176 g HNO3
c. 68 g H2S
Answers for Self Help Study
1. a. 6CO2 + 6H2O
C6H12O6 + 6O2
b. 340.9 g C6H12O6
c. 4.1 g H2O
d. 88 g CO2
2.
.84 kg H
3. a. 112 g CaO
3. b. 89%