, CHEM 110 - EXAM 2
Chemistry and Biochemistry in Our World
Chamberlain University | 100-Question Original Practice Examination | 2026/2027
1. An equation shows 3H2 + N2 -> 2NH3. How many moles of ammonia form from 6.0 mol of H2 if
nitrogen is abundant?
A) 9.0 mol
B) 2.0 mol
C) 4.0 mol
D) 6.0 mol
Correct Answer: 4.0 mol
Rationale: The balanced reaction uses three moles of hydrogen per two moles of ammonia. Multiply six moles by the
ratio 2/3 to obtain four moles. Ratios from an unbalanced equation cannot give a valid yield. A useful check is to count
each element on both sides and verify equality. The symbolic coefficients also set the mole ratios used in later
calculations.
2. During balancing, what may be changed without altering the identity of a compound?
A) The element symbols
B) Coefficients in front of formulas
C) Ionic charges within formulas
D) Subscripts within formulas
Correct Answer: Coefficients in front of formulas
Rationale: Coefficients scale the number of formula units, while subscripts and symbols identify substances.
Changing H2O to H2O2 would describe a different compound, not simply balance the existing reaction. Always count
atoms after adjusting coefficients. A useful check is to count each element on both sides and verify equality. The
symbolic coefficients also set the mole ratios used in later calculations.
3. A reaction begins with 15 g of reactants in a sealed vessel. What combined mass of products is
expected?
A) 15 g
B) An unknown mass without density
C) 30 g
D) Less than 15 g because gases form
Correct Answer: 15 g
Rationale: Conservation of mass requires total product mass to equal total reactant mass in a closed system.
Gaseous products are still matter even when not visible. Mass can appear lost only when material escapes from the
system. A useful check is to count each element on both sides and verify equality. The symbolic coefficients also set
the mole ratios used in later calculations.
4. Which equation correctly represents decomposition of calcium carbonate upon heating?
A) CaCO3 + O2 -> CaO + CO2
B) CaCO3 -> CaO + CO2
C) CaCO3 + CO2 -> CaO
D) CaCO3 -> Ca + C + O3
CHEM 110 | Exam 2 | Original Practice Examination 1
, Correct Answer: CaCO3 -> CaO + CO2
Rationale: Calcium carbonate thermally decomposes into calcium oxide and carbon dioxide. The equation balances
calcium, carbon, and oxygen atoms on both sides. Adding oxygen or carbon dioxide as a reactant would describe a
different process. A useful check is to count each element on both sides and verify equality. The symbolic coefficients
also set the mole ratios used in later calculations.
5. Hydrochloric acid reacts with zinc, releasing hydrogen gas. Which class best describes the
reaction?
A) Synthesis
B) Double replacement
C) Single replacement
D) Precipitation only
Correct Answer: Single replacement
Rationale: Zinc displaces hydrogen from acid to form zinc chloride and hydrogen gas. A metal replaces an element in
a compound, the signature of a single-replacement reaction. This is also redox because zinc loses electrons. A useful
check is to count each element on both sides and verify equality. The symbolic coefficients also set the mole ratios
used in later calculations.
6. How many oxygen atoms are present on the product side of 2KClO3 -> 2KCl + 3O2?
A) 2
B) 6
C) 3
D) 12
Correct Answer: 6
Rationale: Three diatomic oxygen molecules contain six oxygen atoms. A coefficient multiplies the entire molecular
formula, including its subscripts. Counting only molecules rather than atoms leads to an incorrect atom balance. A
useful check is to count each element on both sides and verify equality. The symbolic coefficients also set the mole
ratios used in later calculations.
7. Which observation most strongly indicates a new chemical substance formed?
A) A new precipitate appears after two clear solutions mix
B) Sugar dissolves in water
C) A metal wire is bent
D) Ice melts into water
Correct Answer: A new precipitate appears after two clear solutions mix
Rationale: Precipitation may indicate formation of a new insoluble compound after ions rearrange. Melting, dissolving,
and bending typically change physical form without changing chemical identity. A precipitate should still be confirmed
through chemical evidence. A useful check is to count each element on both sides and verify equality. The symbolic
coefficients also set the mole ratios used in later calculations.
8. For CH4 + 2O2 -> CO2 + 2H2O, how many moles of oxygen are required for 3 mol methane?
A) 6 mol
B) 1.5 mol
C) 12 mol
D) 3 mol
CHEM 110 | Exam 2 | Original Practice Examination 2
Chemistry and Biochemistry in Our World
Chamberlain University | 100-Question Original Practice Examination | 2026/2027
1. An equation shows 3H2 + N2 -> 2NH3. How many moles of ammonia form from 6.0 mol of H2 if
nitrogen is abundant?
A) 9.0 mol
B) 2.0 mol
C) 4.0 mol
D) 6.0 mol
Correct Answer: 4.0 mol
Rationale: The balanced reaction uses three moles of hydrogen per two moles of ammonia. Multiply six moles by the
ratio 2/3 to obtain four moles. Ratios from an unbalanced equation cannot give a valid yield. A useful check is to count
each element on both sides and verify equality. The symbolic coefficients also set the mole ratios used in later
calculations.
2. During balancing, what may be changed without altering the identity of a compound?
A) The element symbols
B) Coefficients in front of formulas
C) Ionic charges within formulas
D) Subscripts within formulas
Correct Answer: Coefficients in front of formulas
Rationale: Coefficients scale the number of formula units, while subscripts and symbols identify substances.
Changing H2O to H2O2 would describe a different compound, not simply balance the existing reaction. Always count
atoms after adjusting coefficients. A useful check is to count each element on both sides and verify equality. The
symbolic coefficients also set the mole ratios used in later calculations.
3. A reaction begins with 15 g of reactants in a sealed vessel. What combined mass of products is
expected?
A) 15 g
B) An unknown mass without density
C) 30 g
D) Less than 15 g because gases form
Correct Answer: 15 g
Rationale: Conservation of mass requires total product mass to equal total reactant mass in a closed system.
Gaseous products are still matter even when not visible. Mass can appear lost only when material escapes from the
system. A useful check is to count each element on both sides and verify equality. The symbolic coefficients also set
the mole ratios used in later calculations.
4. Which equation correctly represents decomposition of calcium carbonate upon heating?
A) CaCO3 + O2 -> CaO + CO2
B) CaCO3 -> CaO + CO2
C) CaCO3 + CO2 -> CaO
D) CaCO3 -> Ca + C + O3
CHEM 110 | Exam 2 | Original Practice Examination 1
, Correct Answer: CaCO3 -> CaO + CO2
Rationale: Calcium carbonate thermally decomposes into calcium oxide and carbon dioxide. The equation balances
calcium, carbon, and oxygen atoms on both sides. Adding oxygen or carbon dioxide as a reactant would describe a
different process. A useful check is to count each element on both sides and verify equality. The symbolic coefficients
also set the mole ratios used in later calculations.
5. Hydrochloric acid reacts with zinc, releasing hydrogen gas. Which class best describes the
reaction?
A) Synthesis
B) Double replacement
C) Single replacement
D) Precipitation only
Correct Answer: Single replacement
Rationale: Zinc displaces hydrogen from acid to form zinc chloride and hydrogen gas. A metal replaces an element in
a compound, the signature of a single-replacement reaction. This is also redox because zinc loses electrons. A useful
check is to count each element on both sides and verify equality. The symbolic coefficients also set the mole ratios
used in later calculations.
6. How many oxygen atoms are present on the product side of 2KClO3 -> 2KCl + 3O2?
A) 2
B) 6
C) 3
D) 12
Correct Answer: 6
Rationale: Three diatomic oxygen molecules contain six oxygen atoms. A coefficient multiplies the entire molecular
formula, including its subscripts. Counting only molecules rather than atoms leads to an incorrect atom balance. A
useful check is to count each element on both sides and verify equality. The symbolic coefficients also set the mole
ratios used in later calculations.
7. Which observation most strongly indicates a new chemical substance formed?
A) A new precipitate appears after two clear solutions mix
B) Sugar dissolves in water
C) A metal wire is bent
D) Ice melts into water
Correct Answer: A new precipitate appears after two clear solutions mix
Rationale: Precipitation may indicate formation of a new insoluble compound after ions rearrange. Melting, dissolving,
and bending typically change physical form without changing chemical identity. A precipitate should still be confirmed
through chemical evidence. A useful check is to count each element on both sides and verify equality. The symbolic
coefficients also set the mole ratios used in later calculations.
8. For CH4 + 2O2 -> CO2 + 2H2O, how many moles of oxygen are required for 3 mol methane?
A) 6 mol
B) 1.5 mol
C) 12 mol
D) 3 mol
CHEM 110 | Exam 2 | Original Practice Examination 2
