CHEM 103 Module 3 Exam (Latest 2026) / CHEM103
General Chemistry I Portage Learning
INTRODUCTION
This question bank is designed for students preparing for the CHEM 103
Module 3 Exam and related general chemistry course exams at colleges
and universities across the United States. It contains unique, non-
repetitive multiple-choice questions with verified answers and detailed
rationales, covering the full exam blueprint: stoichiometry and the mole
concept (molar mass, Avogadro's number, balancing equations, mole
ratios, empirical and molecular formulas, percent composition), gas laws
and thermochemistry (Boyle's Law, Charles's Law, Gay-Lussac's Law,
combined gas law, ideal gas law, STP, specific heat, enthalpy, endothermic
and exothermic reactions, calorimetry), solution chemistry and molarity
(molarity calculations, dilution, solution preparation, precipitation
reactions, acid-base neutralization), advanced stoichiometry and limiting
reagents (limiting reagent identification, theoretical yield, percent yield,
excess reagent), and comprehensive review with integrated problems
(combined stoichiometry, gas laws, thermochemistry, and solution
chemistry).
SECTION 1: STOICHIOMETRY & THE MOLE CONCEPT
,Question 1
What is the correct definition of an exothermic reaction?
A) A reaction that absorbs heat from the surroundings
B) A reaction that releases heat into the surroundings
C) A reaction where the temperature of the system decreases
D) A reaction where ΔH is positive
Correct Answer: B
Rationale: Exothermic reactions release energy, usually in the form
of heat, causing the temperature of the surroundings to rise. In
these reactions, the enthalpy change (ΔH) is always negative.
Question 2
In stoichiometry, the mole ratio between substances is obtained from
which source?
A) Atomic masses on the periodic table
B) Balanced chemical equation coefficients
C) Molecular structure diagrams
D) Reaction temperature
Correct Answer: B
Rationale: The coefficients in a balanced chemical equation
represent the relative number of moles of each substance involved
in the reaction.
,Question 3
How many moles are present in 36.0 g of water (H₂O)?
A) 1 mol
B) 2 mol
C) 3 mol
D) 4 mol
Correct Answer: B
Rationale: The molar mass of H₂O is 18 g/mol. 36 g ÷ 18 g/mol = 2
mol.
Question 4
What is the molar mass of CO₂?
A) 28 g/mol
B) 40 g/mol
C) 44 g/mol
D) 48 g/mol
Correct Answer: C
Rationale: Carbon has a mass of 12 g/mol and oxygen is 16 g/mol.
CO₂ = 12 + (16 × 2) = 44 g/mol.
, Question 5
Balance the equation: H₂ + O₂ → H₂O
A) 1,1,1
B) 2,1,2
C) 1,2,1
D) 2,2,2
Correct Answer: B
Rationale: Two molecules of hydrogen react with one molecule of
oxygen to produce two molecules of water. The balanced equation is
2H₂ + O₂ → 2H₂O.
Question 6
How many moles are in 22.4 L of gas at STP?
A) 0.5 mol
B) 1 mol
C) 2 mol
D) 10 mol
Correct Answer: B
Rationale: At STP, 1 mole of any ideal gas occupies 22.4 liters.
General Chemistry I Portage Learning
INTRODUCTION
This question bank is designed for students preparing for the CHEM 103
Module 3 Exam and related general chemistry course exams at colleges
and universities across the United States. It contains unique, non-
repetitive multiple-choice questions with verified answers and detailed
rationales, covering the full exam blueprint: stoichiometry and the mole
concept (molar mass, Avogadro's number, balancing equations, mole
ratios, empirical and molecular formulas, percent composition), gas laws
and thermochemistry (Boyle's Law, Charles's Law, Gay-Lussac's Law,
combined gas law, ideal gas law, STP, specific heat, enthalpy, endothermic
and exothermic reactions, calorimetry), solution chemistry and molarity
(molarity calculations, dilution, solution preparation, precipitation
reactions, acid-base neutralization), advanced stoichiometry and limiting
reagents (limiting reagent identification, theoretical yield, percent yield,
excess reagent), and comprehensive review with integrated problems
(combined stoichiometry, gas laws, thermochemistry, and solution
chemistry).
SECTION 1: STOICHIOMETRY & THE MOLE CONCEPT
,Question 1
What is the correct definition of an exothermic reaction?
A) A reaction that absorbs heat from the surroundings
B) A reaction that releases heat into the surroundings
C) A reaction where the temperature of the system decreases
D) A reaction where ΔH is positive
Correct Answer: B
Rationale: Exothermic reactions release energy, usually in the form
of heat, causing the temperature of the surroundings to rise. In
these reactions, the enthalpy change (ΔH) is always negative.
Question 2
In stoichiometry, the mole ratio between substances is obtained from
which source?
A) Atomic masses on the periodic table
B) Balanced chemical equation coefficients
C) Molecular structure diagrams
D) Reaction temperature
Correct Answer: B
Rationale: The coefficients in a balanced chemical equation
represent the relative number of moles of each substance involved
in the reaction.
,Question 3
How many moles are present in 36.0 g of water (H₂O)?
A) 1 mol
B) 2 mol
C) 3 mol
D) 4 mol
Correct Answer: B
Rationale: The molar mass of H₂O is 18 g/mol. 36 g ÷ 18 g/mol = 2
mol.
Question 4
What is the molar mass of CO₂?
A) 28 g/mol
B) 40 g/mol
C) 44 g/mol
D) 48 g/mol
Correct Answer: C
Rationale: Carbon has a mass of 12 g/mol and oxygen is 16 g/mol.
CO₂ = 12 + (16 × 2) = 44 g/mol.
, Question 5
Balance the equation: H₂ + O₂ → H₂O
A) 1,1,1
B) 2,1,2
C) 1,2,1
D) 2,2,2
Correct Answer: B
Rationale: Two molecules of hydrogen react with one molecule of
oxygen to produce two molecules of water. The balanced equation is
2H₂ + O₂ → 2H₂O.
Question 6
How many moles are in 22.4 L of gas at STP?
A) 0.5 mol
B) 1 mol
C) 2 mol
D) 10 mol
Correct Answer: B
Rationale: At STP, 1 mole of any ideal gas occupies 22.4 liters.
