MCQ 91:
Which of the following statements about the rate of reaction is correct?
A) It decreases as the concentration of reactants decreases.
B) It remains constant throughout the reaction.
C) It is always directly proportional to the temperature.
D) It increases with decreasing surface area.
Answer: A) It decreases as the concentration of reactants decreases.
Explanation: As reactants are consumed, their concentrations decrease, leading to a reduction in the reaction rate.
MCQ 92:
Which of the following is an example of a catalyst in a biological reaction?
A) Oxygen
B) Enzyme
C) Water
D) Acid
Answer: B) Enzyme
Explanation: Enzymes are biological catalysts that speed up biochemical reactions without being consumed in the process.
MCQ 93:
What does a high value of the equilibrium constant (K) indicate about a reaction?
A) The reaction favors reactants at equilibrium.
B) The reaction favors products at equilibrium.
C) The reaction proceeds very slowly.
D) The reaction is at equilibrium.
Answer: B) The reaction favors products at equilibrium.
Explanation: A high K value means that at equilibrium, the concentration of products is much greater than that of reactants.
MCQ 94:
Which of the following factors can change the position of equilibrium in a system?
A) Temperature
B) Concentration of reactants or products
C) Pressure (in gaseous reactions)
D) All of the above
Answer: D) All of the above
Explanation: Changes in temperature, concentration, or pressure can shift the position of equilibrium in a reversible reaction.
MCQ 95:
In a reaction that involves gases, what effect does increasing the volume of the container have on the equilibrium position?
A) It shifts to the side with fewer moles of gas.
B) It shifts to the side with more moles of gas.
C) It has no effect on the equilibrium position.
D) It stops the reaction.
Answer: B) It shifts to the side with more moles of gas.
Explanation: Increasing the volume decreases the pressure, favoring the side of the reaction that produces more moles of gas.
MCQ 96:
Which of the following is a characteristic of a first-order reaction?
A) The rate depends on the concentration of one reactant raised to the second power.
B) The half-life is constant and independent of the initial concentration.
C) The rate doubles if the concentration of reactants is doubled.
D) The reaction is not affected by temperature changes.
Answer: C) The rate doubles if the concentration of reactants is doubled.
Explanation: In a first-order reaction, doubling the concentration of the reactant leads to a doubling of the reaction rate.
MCQ 97:
Which of the following statements about reaction mechanisms is false?
A) A reaction mechanism consists of a series of elementary steps.
B) The rate-determining step is always the fastest step.
C) Intermediates are formed and consumed during the reaction.
D) The sum of the elementary steps gives the overall balanced equation.
Answer: B) The rate-determining step is always the fastest step.
Explanation: The rate-determining step is actually the slowest step in the mechanism that limits the overall rate of the reaction.
MCQ 98:
What is the effect of increasing pressure on a reaction that produces fewer moles of gas?
A) The reaction shifts to the right.
B) The reaction shifts to the left.
C) The reaction rate decreases.
D) There is no effect on the reaction.
Answer: A) The reaction shifts to the right.
Explanation: Increasing pressure favors the side of the reaction that produces fewer moles of gas, shifting the equilibrium to the right.
MCQ 99:
In the context of reaction kinetics, what does the term “half-life” refer to?
A) The time required for half of the reactants to be converted to products.
B) The time it takes for the reaction to reach completion.
C) The time it takes for the rate of the reaction to decrease by half.
D) The time required for the concentration of a reactant to reach equilibrium.
Answer: A) The time required for half of the reactants to be converted to products.
Explanation: The half-life is a measure of the time it takes for the concentration of a reactant to decrease to half its initial value.
MCQ 100:
In an exothermic reaction, what effect does adding more reactant have on the equilibrium position?
A) It shifts to the right.
B) It shifts to the left.
C) It remains unchanged.
D) It causes the reaction to stop.
Answer: A) It shifts to the right.
Explanation: Adding more reactant increases its concentration, which shifts the equilibrium position to favor the formation of products.
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