UNE General Chemistry II Midterm Actual Exam 200
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Graded A+
1. Which of the following statements correctly describes the collision
theory of reaction rates?
A) Reactions occur only when molecules collide with sufficient energy
and proper orientation
B) All molecular collisions result in a chemical reaction
C) The rate of reaction is independent of the collision frequency
D) Activation energy is not required for a reaction to occur
E) Temperature has no effect on the collision rate
Correct Answer: A
Explanation: Collision theory states that for a reaction to occur, reactant
molecules must collide with sufficient kinetic energy (equal to or greater
than the activation energy) and with the correct spatial orientation. Not
all collisions lead to products; only those meeting both criteria are
effective. Temperature increases collision frequency and energy,
affecting reaction rates.
2. For the reaction 2A + B → C, the rate law is determined to be Rate =
k[A]²[B]. What is the overall order of the reaction?
A) 0
,B) 1
C) 2
D) 3
E) Cannot be determined from the information given
Correct Answer: D
Explanation: The overall order of a reaction is the sum of the individual
orders with respect to each reactant. Here, the reaction is second order
with respect to A (exponent 2) and first order with respect to B
(exponent 1). Therefore, the overall order is 2 + 1 = 3, making this a
third-order reaction overall.
3. Which factor 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
E) Surface area of solid reactants
Correct Answer: D
Explanation: The equilibrium constant (K) is a thermodynamic quantity
that indicates the extent of a reaction at equilibrium, not the rate at
which equilibrium is achieved. Temperature, concentration, catalysts,
and surface area all affect reaction kinetics by influencing collision
frequency, energy, or reaction pathway. The equilibrium constant
remains unchanged by catalysts and does not directly determine
reaction speed.
,4. The half-life of a first-order reaction is 30 minutes. What percentage
of the original reactant remains after 90 minutes?
A) 50%
B) 25%
C) 12.5%
D) 6.25%
E) 3.125%
Correct Answer: C
Explanation: For a first-order reaction, each half-life reduces the
concentration by half. After 90 minutes, which equals three half-lives
(90/30 = 3), the remaining fraction is (1/2)³ = 1/8 = 0.125. Converting to
percentage: 0.125 × 100% = 12.5% of the original reactant remains. The
other options represent 1, 2, 4, and 5 half-lives respectively.
5. Which of the following is a characteristic of a catalyst?
A) It is consumed during the reaction
B) It increases the activation energy of the reaction
C) It provides an alternative reaction pathway with lower activation
energy
D) It changes the equilibrium position of the reaction
E) It affects the thermodynamics of the reaction
Correct Answer: C
Explanation: A catalyst works by providing an alternative reaction
mechanism with a lower activation energy, thereby increasing the
reaction rate. It is not consumed in the reaction and can be recovered
unchanged. Catalysts do not affect the equilibrium position or the
, thermodynamics (ΔG, ΔH, ΔS) of the reaction; they only speed up the
attainment of equilibrium.
6. For the equilibrium reaction N₂O₄(g) ⇌ 2NO₂(g), which change
would shift the equilibrium to the right (toward products)?
A) Decreasing the temperature (reaction is endothermic)
B) Increasing the pressure by decreasing the volume
C) Adding a catalyst
D) Removing NO₂ from the reaction mixture
E) Adding an inert gas at constant volume
Correct Answer: D
Explanation: According to Le Châtelier's principle, removing a product
(NO₂) from the equilibrium mixture will shift the equilibrium to the right
to produce more NO₂ and re-establish equilibrium. Decreasing
temperature for an endothermic reaction favors reactants. Increasing
pressure favors the side with fewer gas moles (reactants). Catalysts do
not shift equilibrium. Adding inert gas at constant volume does not
change partial pressures and thus does not shift equilibrium.
7. The equilibrium constant Kc for the reaction H₂(g) + I₂(g) ⇌ 2HI(g) is
50 at a certain temperature. If the initial concentrations are [H₂] = 0.5
M and [I₂] = 0.5 M, what is the approximate equilibrium concentration
of HI?
A) 0.25 M
B) 0.50 M
C) 0.78 M
Questions and Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download PDF Already
Graded A+
1. Which of the following statements correctly describes the collision
theory of reaction rates?
A) Reactions occur only when molecules collide with sufficient energy
and proper orientation
B) All molecular collisions result in a chemical reaction
C) The rate of reaction is independent of the collision frequency
D) Activation energy is not required for a reaction to occur
E) Temperature has no effect on the collision rate
Correct Answer: A
Explanation: Collision theory states that for a reaction to occur, reactant
molecules must collide with sufficient kinetic energy (equal to or greater
than the activation energy) and with the correct spatial orientation. Not
all collisions lead to products; only those meeting both criteria are
effective. Temperature increases collision frequency and energy,
affecting reaction rates.
2. For the reaction 2A + B → C, the rate law is determined to be Rate =
k[A]²[B]. What is the overall order of the reaction?
A) 0
,B) 1
C) 2
D) 3
E) Cannot be determined from the information given
Correct Answer: D
Explanation: The overall order of a reaction is the sum of the individual
orders with respect to each reactant. Here, the reaction is second order
with respect to A (exponent 2) and first order with respect to B
(exponent 1). Therefore, the overall order is 2 + 1 = 3, making this a
third-order reaction overall.
3. Which factor 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
E) Surface area of solid reactants
Correct Answer: D
Explanation: The equilibrium constant (K) is a thermodynamic quantity
that indicates the extent of a reaction at equilibrium, not the rate at
which equilibrium is achieved. Temperature, concentration, catalysts,
and surface area all affect reaction kinetics by influencing collision
frequency, energy, or reaction pathway. The equilibrium constant
remains unchanged by catalysts and does not directly determine
reaction speed.
,4. The half-life of a first-order reaction is 30 minutes. What percentage
of the original reactant remains after 90 minutes?
A) 50%
B) 25%
C) 12.5%
D) 6.25%
E) 3.125%
Correct Answer: C
Explanation: For a first-order reaction, each half-life reduces the
concentration by half. After 90 minutes, which equals three half-lives
(90/30 = 3), the remaining fraction is (1/2)³ = 1/8 = 0.125. Converting to
percentage: 0.125 × 100% = 12.5% of the original reactant remains. The
other options represent 1, 2, 4, and 5 half-lives respectively.
5. Which of the following is a characteristic of a catalyst?
A) It is consumed during the reaction
B) It increases the activation energy of the reaction
C) It provides an alternative reaction pathway with lower activation
energy
D) It changes the equilibrium position of the reaction
E) It affects the thermodynamics of the reaction
Correct Answer: C
Explanation: A catalyst works by providing an alternative reaction
mechanism with a lower activation energy, thereby increasing the
reaction rate. It is not consumed in the reaction and can be recovered
unchanged. Catalysts do not affect the equilibrium position or the
, thermodynamics (ΔG, ΔH, ΔS) of the reaction; they only speed up the
attainment of equilibrium.
6. For the equilibrium reaction N₂O₄(g) ⇌ 2NO₂(g), which change
would shift the equilibrium to the right (toward products)?
A) Decreasing the temperature (reaction is endothermic)
B) Increasing the pressure by decreasing the volume
C) Adding a catalyst
D) Removing NO₂ from the reaction mixture
E) Adding an inert gas at constant volume
Correct Answer: D
Explanation: According to Le Châtelier's principle, removing a product
(NO₂) from the equilibrium mixture will shift the equilibrium to the right
to produce more NO₂ and re-establish equilibrium. Decreasing
temperature for an endothermic reaction favors reactants. Increasing
pressure favors the side with fewer gas moles (reactants). Catalysts do
not shift equilibrium. Adding inert gas at constant volume does not
change partial pressures and thus does not shift equilibrium.
7. The equilibrium constant Kc for the reaction H₂(g) + I₂(g) ⇌ 2HI(g) is
50 at a certain temperature. If the initial concentrations are [H₂] = 0.5
M and [I₂] = 0.5 M, what is the approximate equilibrium concentration
of HI?
A) 0.25 M
B) 0.50 M
C) 0.78 M
