,CHEM 121 Module 6 Exam Foundations of General
Chemistry w/Lab | Portage | 26/27 Actual (PDF)
1. Which statement correctly defines the rate of a chemical reaction?
A) The total amount of product formed when the reaction reaches completion.
B) The change in concentration of a reactant or product per unit time.
C) The energy released per mole of reactant consumed during the reaction.
D) The time required for all reactants to be completely converted to products.
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, option C describes enthalpy
change, and option D describes the total reaction time, none of which define 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.
B) The molecules must collide with proper orientation.
Chemistry w/Lab | Portage | 26/27 Actual (PDF)
1. Which statement correctly defines the rate of a chemical reaction?
A) The total amount of product formed when the reaction reaches completion.
B) The change in concentration of a reactant or product per unit time.
C) The energy released per mole of reactant consumed during the reaction.
D) The time required for all reactants to be completely converted to products.
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, option C describes enthalpy
change, and option D describes the total reaction time, none of which define 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.
B) The molecules must collide with proper orientation.
