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,HEM 104 Module 5 Exam General Chemistry II
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. The rate of a chemical reaction is defined as which of the following quantities?
A) The total amount of product formed at the end of the reaction.
B) The change in concentration of a reactant or product per unit time.
C) The energy released per mole of reactant consumed.
D) The time required for the reaction to reach completion.
Correct Answer: The change in concentration of a reactant or product per unit time.
Rationale: Reaction rate is defined as the change in concentration of a reactant or product per unit
time, typically expressed in mol/(L·s). Option A describes the final yield, not the rate. Option C
describes enthalpy change, and option D describes the total reaction time, neither of which defines
rate.
2. For the reaction 2 N2O5(g) → 4 NO2(g) + O2(g), if the rate of disappearance of N2O5 is 0.020 M/s,
what is the rate of appearance of NO2?
A) 0.010 M/s
B) 0.020 M/s
C) 0.040 M/s
D) 0.080 M/s
,Correct Answer: 0.040 M/s
Rationale: The rate relationship is derived from stoichiometry: rate = -(1/2)Δ[N2O5]/Δt =
(1/4)Δ[NO2]/Δt. Therefore, Δ[NO2]/Δt = (4/2)(0.020) = 0.040 M/s. Option A incorrectly uses a 1:1
ratio, and options B and D ignore the stoichiometric coefficients.
3. Which of the following factors generally does NOT affect the rate of a chemical reaction?
A) Temperature
B) Concentration of reactants
C) Presence of a catalyst
D) The equilibrium constant of the reaction
Correct Answer: The equilibrium constant of the reaction
Rationale: The equilibrium constant describes the extent of a reaction at equilibrium, not how fast it
reaches equilibrium. Temperature, concentration, and catalysts all affect reaction rate. The
equilibrium constant is a thermodynamic property and does not determine kinetic rate.
4. The rate law for a reaction is determined experimentally to be Rate = k[A]^2[B]. What is the overall
reaction order?
A) First order
B) Second order
, C) Third order
D) Fourth order
Correct Answer: Third order
Rationale: The overall reaction order is the sum of the individual orders: 2 (for A) + 1 (for B) = 3.
Option A represents a first-order reaction, option B represents a second-order reaction, and option D
would require an additional order of one.
5. For a first-order reaction with a rate constant of 0.025 s^-1, what is the half-life?
A) 27.7 s
B) 40.0 s
C) 0.025 s
D) 17.3 s
Correct Answer: 27.7 s
Rationale: For a first-order reaction, t1/2 = 0.693/k = 0.693/0.025 = 27.7 s. Option B is the reciprocal of
the rate constant, option C is the rate constant itself, and option D is an incorrect calculation.
6. According to collision theory, which condition is NOT required for a reaction to occur between two
molecules?
A) The molecules must collide with sufficient energy.
,HEM 104 Module 5 Exam General Chemistry II
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. The rate of a chemical reaction is defined as which of the following quantities?
A) The total amount of product formed at the end of the reaction.
B) The change in concentration of a reactant or product per unit time.
C) The energy released per mole of reactant consumed.
D) The time required for the reaction to reach completion.
Correct Answer: The change in concentration of a reactant or product per unit time.
Rationale: Reaction rate is defined as the change in concentration of a reactant or product per unit
time, typically expressed in mol/(L·s). Option A describes the final yield, not the rate. Option C
describes enthalpy change, and option D describes the total reaction time, neither of which defines
rate.
2. For the reaction 2 N2O5(g) → 4 NO2(g) + O2(g), if the rate of disappearance of N2O5 is 0.020 M/s,
what is the rate of appearance of NO2?
A) 0.010 M/s
B) 0.020 M/s
C) 0.040 M/s
D) 0.080 M/s
,Correct Answer: 0.040 M/s
Rationale: The rate relationship is derived from stoichiometry: rate = -(1/2)Δ[N2O5]/Δt =
(1/4)Δ[NO2]/Δt. Therefore, Δ[NO2]/Δt = (4/2)(0.020) = 0.040 M/s. Option A incorrectly uses a 1:1
ratio, and options B and D ignore the stoichiometric coefficients.
3. Which of the following factors generally does NOT affect the rate of a chemical reaction?
A) Temperature
B) Concentration of reactants
C) Presence of a catalyst
D) The equilibrium constant of the reaction
Correct Answer: The equilibrium constant of the reaction
Rationale: The equilibrium constant describes the extent of a reaction at equilibrium, not how fast it
reaches equilibrium. Temperature, concentration, and catalysts all affect reaction rate. The
equilibrium constant is a thermodynamic property and does not determine kinetic rate.
4. The rate law for a reaction is determined experimentally to be Rate = k[A]^2[B]. What is the overall
reaction order?
A) First order
B) Second order
, C) Third order
D) Fourth order
Correct Answer: Third order
Rationale: The overall reaction order is the sum of the individual orders: 2 (for A) + 1 (for B) = 3.
Option A represents a first-order reaction, option B represents a second-order reaction, and option D
would require an additional order of one.
5. For a first-order reaction with a rate constant of 0.025 s^-1, what is the half-life?
A) 27.7 s
B) 40.0 s
C) 0.025 s
D) 17.3 s
Correct Answer: 27.7 s
Rationale: For a first-order reaction, t1/2 = 0.693/k = 0.693/0.025 = 27.7 s. Option B is the reciprocal of
the rate constant, option C is the rate constant itself, and option D is an incorrect calculation.
6. According to collision theory, which condition is NOT required for a reaction to occur between two
molecules?
A) The molecules must collide with sufficient energy.
