Chem 103 Module 3 Exam 2026
Chem 103 Module 3 Exam 2026 Edition 100
Advanced Questions with Answers and
Detailed Rationales
These 100 original practice questions covers key CHEM 103 Module 3 topics,
including:
Stoichiometry and mole conversions
Limiting reactants and percent yield
Empirical and molecular formulas
Gas laws (Boyle's, Charles's, Gay-Lussac's, Combined, and Ideal Gas Law)
Dalton's law of partial pressures
Molarity and solution calculations
Kinetic molecular theory
Gas stoichiometry and multi-step calculations
Question 1
A sample contains 3.01 × 10²³ molecules of CO₂. How many moles of CO₂ are present?
A. 0.25 mol
B. 0.50 mol
C. 1.00 mol
D. 2.00 mol
Answer: B. 0.50 mol
Rationale: One mole contains 6.022 × 10²³ molecules.
3.01×10236.022×1023=0.50 mol\frac{3.01 \times 10^{23}}{6.022 \times
10^{23}}=0.50\text{ mol}6.022×10233.01×1023=0.50 mol
Question 2
, Chem 103 Module 3 Exam 2026
How many grams are in 2.50 mol of NaCl?
(Molar mass NaCl = 58.44 g/mol)
A. 58.44 g
B. 87.66 g
C. 116.88 g
D. 146.10 g
Answer: D. 146.10 g
Rationale:
2.50×58.44=146.10 g2.50 \times 58.44=146.10\text{ g}2.50×58.44=146.10 g
Question 3
What is the empirical formula of a compound that is 40.0% carbon, 6.7% hydrogen, and
53.3% oxygen?
A. CH₂O
B. C₂H₄O₂
C. CHO
D. C₃H₆O₃
Answer: A. CH₂O
Rationale: Converting percentages to moles and dividing by the smallest value gives
the ratio 1 : 2 : 1.
Question 4
According to the ideal gas law, if pressure doubles while temperature and moles
remain constant, the gas volume will:
, Chem 103 Module 3 Exam 2026
A. Double
B. Remain unchanged
C. Be cut in half
D. Triple
Answer: C. Be cut in half
Rationale: Boyle's Law states:
P1V1=P2V2P_1V_1=P_2V_2P1V1=P2V2
Pressure and volume are inversely proportional.
Question 5
How many liters will 1.50 mol of an ideal gas occupy at STP?
A. 11.2 L
B. 22.4 L
C. 33.6 L
D. 44.8 L
Answer: C. 33.6 L
Rationale:
At STP:
1 mol=22.4 L1\text{ mol}=22.4\text{ L}1 mol=22.4 L
1.5×22.4=33.6 L1.5\times22.4=33.6\text{ L}1.5×22.4=33.6 L
Question 6
Which law describes the direct relationship between temperature and volume?
, Chem 103 Module 3 Exam 2026
A. Boyle's Law
B. Charles's Law
C. Dalton's Law
D. Avogadro's Law
Answer: B. Charles's Law
Rationale: Charles's Law states that at constant pressure, gas volume increases directly
with absolute temperature.
Question 7
A reaction theoretically produces 25.0 g of product but actually yields 20.0 g. What is
the percent yield?
A. 60%
B. 70%
C. 80%
D. 90%
Answer: C. 80%
Rationale:
20.025.0×100=80%\frac{20.0}{25.0}\times100=80\%25.020.0×100=80%
Question 8
Which quantity remains constant in a balanced chemical equation?
A. Number of molecules
B. Total mass
C. Volume
Chem 103 Module 3 Exam 2026 Edition 100
Advanced Questions with Answers and
Detailed Rationales
These 100 original practice questions covers key CHEM 103 Module 3 topics,
including:
Stoichiometry and mole conversions
Limiting reactants and percent yield
Empirical and molecular formulas
Gas laws (Boyle's, Charles's, Gay-Lussac's, Combined, and Ideal Gas Law)
Dalton's law of partial pressures
Molarity and solution calculations
Kinetic molecular theory
Gas stoichiometry and multi-step calculations
Question 1
A sample contains 3.01 × 10²³ molecules of CO₂. How many moles of CO₂ are present?
A. 0.25 mol
B. 0.50 mol
C. 1.00 mol
D. 2.00 mol
Answer: B. 0.50 mol
Rationale: One mole contains 6.022 × 10²³ molecules.
3.01×10236.022×1023=0.50 mol\frac{3.01 \times 10^{23}}{6.022 \times
10^{23}}=0.50\text{ mol}6.022×10233.01×1023=0.50 mol
Question 2
, Chem 103 Module 3 Exam 2026
How many grams are in 2.50 mol of NaCl?
(Molar mass NaCl = 58.44 g/mol)
A. 58.44 g
B. 87.66 g
C. 116.88 g
D. 146.10 g
Answer: D. 146.10 g
Rationale:
2.50×58.44=146.10 g2.50 \times 58.44=146.10\text{ g}2.50×58.44=146.10 g
Question 3
What is the empirical formula of a compound that is 40.0% carbon, 6.7% hydrogen, and
53.3% oxygen?
A. CH₂O
B. C₂H₄O₂
C. CHO
D. C₃H₆O₃
Answer: A. CH₂O
Rationale: Converting percentages to moles and dividing by the smallest value gives
the ratio 1 : 2 : 1.
Question 4
According to the ideal gas law, if pressure doubles while temperature and moles
remain constant, the gas volume will:
, Chem 103 Module 3 Exam 2026
A. Double
B. Remain unchanged
C. Be cut in half
D. Triple
Answer: C. Be cut in half
Rationale: Boyle's Law states:
P1V1=P2V2P_1V_1=P_2V_2P1V1=P2V2
Pressure and volume are inversely proportional.
Question 5
How many liters will 1.50 mol of an ideal gas occupy at STP?
A. 11.2 L
B. 22.4 L
C. 33.6 L
D. 44.8 L
Answer: C. 33.6 L
Rationale:
At STP:
1 mol=22.4 L1\text{ mol}=22.4\text{ L}1 mol=22.4 L
1.5×22.4=33.6 L1.5\times22.4=33.6\text{ L}1.5×22.4=33.6 L
Question 6
Which law describes the direct relationship between temperature and volume?
, Chem 103 Module 3 Exam 2026
A. Boyle's Law
B. Charles's Law
C. Dalton's Law
D. Avogadro's Law
Answer: B. Charles's Law
Rationale: Charles's Law states that at constant pressure, gas volume increases directly
with absolute temperature.
Question 7
A reaction theoretically produces 25.0 g of product but actually yields 20.0 g. What is
the percent yield?
A. 60%
B. 70%
C. 80%
D. 90%
Answer: C. 80%
Rationale:
20.025.0×100=80%\frac{20.0}{25.0}\times100=80\%25.020.0×100=80%
Question 8
Which quantity remains constant in a balanced chemical equation?
A. Number of molecules
B. Total mass
C. Volume
