MCQ 11:
Which of the following factors can change the equilibrium constant of a reaction?
A) Concentration of reactants
B) Temperature
C) Pressure
D) Catalyst
Answer: B) Temperature
Explanation: The equilibrium constant for a reaction is affected by temperature changes. The concentrations of reactants and products at equilibrium do not change the value of the equilibrium constant.
MCQ 12:
Which of the following statements about a catalyst is FALSE?
A) Catalysts are consumed in the reaction.
B) Catalysts lower activation energy.
C) Catalysts can be recovered unchanged after the reaction.
D) Catalysts speed up the rate of reaction.
Answer: A) Catalysts are consumed in the reaction.
Explanation: Catalysts are not consumed during the reaction; they remain unchanged and can be reused.
MCQ 13:
What type of reaction is characterized by the formation of an intermediate species?
A) Combustion
B) Chain reaction
C) Reversible reaction
D) Photochemical reaction
Answer: B) Chain reaction
Explanation: In a chain reaction, reactive intermediates are formed and consumed in a cyclic manner, often leading to rapid propagation of the reaction.
MCQ 14:
For a reaction to occur, what must happen between reactant molecules?
A) They must collide.
B) They must be at high pressure.
C) They must be in the same phase.
D) They must absorb heat.
Answer: A) They must collide.
Explanation: For a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation to break bonds and form new products.
MCQ 15:
In a zero-order reaction, the rate of reaction:
A) Increases with increasing concentration of reactants.
B) Is constant and independent of reactant concentration.
C) Decreases as reactants are consumed.
D) Is proportional to the square of the concentration of reactants.
Answer: B) Is constant and independent of reactant concentration.
Explanation: In a zero-order reaction, the rate is constant and does not depend on the concentration of the reactants.
MCQ 16:
Which of the following will likely increase the rate of a reaction involving gases?
A) Decreasing the volume of the reaction vessel
B) Increasing the temperature
C) Increasing the concentration of the reactants
D) All of the above
Answer: D) All of the above
Explanation: All these factors—decreasing the volume (which increases pressure), increasing temperature, and increasing concentration—will generally increase the rate of reaction for gaseous reactants.
MCQ 17:
Which of the following is an example of a heterogeneous catalyst?
A) Platinum in catalytic converters
B) Enzymes
C) Iron in the Haber process
D) Sodium hydroxide in acid-base reactions
Answer: C) Iron in the Haber process
Explanation: Iron acts as a solid catalyst in the Haber process for ammonia synthesis, making it a heterogeneous catalyst, as it is in a different phase than the gaseous reactants.
MCQ 18:
The rate of a chemical reaction is typically measured in terms of:
A) Volume of reactants consumed
B) Mass of products formed per unit time
C) Change in concentration of reactants or products per unit time
D) Temperature change
Answer: C) Change in concentration of reactants or products per unit time
Explanation: The rate of reaction is defined as the change in concentration of a reactant or product over a specific time interval.
MCQ 19:
A reaction is described as being “first order” with respect to a particular reactant if:
A) The rate of reaction is independent of the concentration of that reactant.
B) The rate of reaction is proportional to the square of the concentration of that reactant.
C) The rate of reaction is directly proportional to the concentration of that reactant.
D) The reaction does not occur.
Answer: C) The rate of reaction is directly proportional to the concentration of that reactant.
Explanation: A first-order reaction shows a linear relationship where the rate increases proportionally with the concentration of that reactant.
MCQ 20:
What happens to the rate of a reaction when a reactant is in excess?
A) The rate decreases.
B) The rate remains unchanged.
C) The rate increases significantly.
D) The reaction stops.
Answer: B) The rate remains unchanged.
Explanation: If one reactant is in excess, the rate of the reaction is primarily dependent on the concentration of the limiting reactant, so the rate remains unchanged until that reactant is consumed.
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