Question 41
In a chemical reaction, if the rate of reaction is dependent on the square of the concentration of A, the reaction is classified as:
A) Zero-order
B) First-order
C) Second-order
D) Third-order
Answer: C) Second-order
Explanation: A reaction that depends on the square of the concentration of one reactant (e.g., Rate=k[A]2 is classified as second-order with respect to that reactant.
Question 42
The rate of a chemical reaction increases with temperature because:
A) The molecules collide less frequently.
B) The activation energy decreases.
C) The average kinetic energy of the molecules increases.
D) The concentration of reactants decreases.
Answer: C) The average kinetic energy of the molecules increases.
Explanation: An increase in temperature raises the kinetic energy of molecules, leading to more frequent and energetic collisions, which increases the reaction rate.
Question 43
A reaction mechanism consists of multiple steps. The rate of the overall reaction is determined by:
A) The fast step
B) The slowest step
C) The intermediate step
D) The first step
Answer: B) The slowest step
Explanation: The overall rate of a reaction is determined by the rate-determining step, which is the slowest step in the mechanism.
Question 44
For a first-order reaction, if the concentration of the reactant decreases from 0.1 M to 0.05 M, the rate will:
A) Stay the same
B) Double
C) Halve
D) Decrease by a factor of 4
Answer: C) Halve
Explanation: For a first-order reaction, the rate is directly proportional to the concentration of the reactant. If the concentration is halved, the rate also halves.
Question 45
The reaction A+2B→C has a rate law of Rate=k[A]2[B]. What is the reaction order with respect to A?
A) 1
B) 2
C) 3
D) 4
Answer: B) 2
Explanation: The order with respect to A is given by the exponent in the rate law, which is 2.
Question 46
If a reaction is found to have an activation energy of 75 kJ/mol, what effect would increasing the temperature have on the reaction?
A) No effect on rate
B) Decrease the rate
C) Increase the rate
D) Change the activation energy
Answer: C) Increase the rate
Explanation: Increasing the temperature typically increases the rate of a reaction by providing more molecules with enough energy to overcome the activation energy barrier.
Question 47
What is the overall order of the reaction represented by the rate law Rate=k[A][B]2?
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: The overall order of the reaction is the sum of the exponents in the rate law: 1+2=3
Question 48
Which of the following reactions would most likely be zero-order?
A) A→Products with a constant rate
B) 2A→Products
C) A+B→Products
D) A+2B→Products
Answer: A) A→Products with a constant rate
Explanation: A zero-order reaction has a constant rate that does not depend on the concentration of the reactant(s).
Question 49
In a reaction mechanism, the species that is formed in one step and consumed in a subsequent step is called:
A) Catalyst
B) Intermediate
C) Reactant
D) Product
Answer: B) Intermediate
Explanation: Intermediates are species that are formed during the reaction mechanism but do not appear in the overall balanced equation.
Question 50
For a reaction that is second-order with respect to reactant A, the half-life is:
A) Constant and independent of initial concentration
B) Inversely proportional to initial concentration
C) Directly proportional to initial concentration
D) Unrelated to the concentration
Answer: B) Inversely proportional to initial concentration
Explanation: In second-order reactions, the half-life is inversely proportional to the initial concentration of the reactant.
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