Try each question on your own first. Use the Show Answer button only after you have selected your option, then read the explanation and revise the related concept from your chapter notes.
1. The order of a chemical reaction is determined:
A. Experimentally from the rate law
B. From the stoichiometry of the balanced equation
C. From molecularity
D. From theoretical calculation only
Answer: A. Experimentally from the rate law
Explanation: Order is an experimental quantity found from how rate depends on concentration; it need not match stoichiometric coefficients.
2. The unit of the rate constant for a first order reaction is:
A. s⁻¹
B. mol L⁻¹ s⁻¹
C. L mol⁻¹ s⁻¹
D. mol⁻¹ L² s⁻¹
Answer: A. s⁻¹
Explanation: For a first order reaction, rate = k[A], so k must have units of s⁻¹ to keep rate in mol L⁻¹ s⁻¹.
3. The half-life of a first order reaction is:
A. Independent of the initial concentration
B. Directly proportional to the initial concentration
C. Inversely proportional to the initial concentration
D. Proportional to the square of concentration
Answer: A. Independent of the initial concentration
Explanation: For a first order reaction, t½ = 0.693/k, which does not depend on initial concentration.
4. The rate of a reaction generally increases with a rise in temperature mainly because:
A. The number of effective collisions increases
B. The activation energy decreases
C. The molecularity increases
D. The order of reaction changes
Answer: A. The number of effective collisions increases
Explanation: Higher temperature increases the fraction of molecules with energy greater than the activation energy, increasing effective collisions.
5. The Arrhenius equation is correctly written as:
A. k = A e^(-Ea/RT)
B. k = A + Ea/RT
C. k = A - RT/Ea
D. k = A e^(Ea/RT)
Answer: A. k = A e^(-Ea/RT)
Explanation: The Arrhenius equation relates the rate constant k to the activation energy Ea, temperature T, and pre-exponential factor A.
6. Molecularity of a reaction can never be:
A. Zero or a fraction
B. One
C. Two
D. Three
Answer: A. Zero or a fraction
Explanation: Molecularity is the number of reacting species in an elementary step, so it must be a whole number and cannot be zero or fractional (unlike order).
7. A zero order reaction has a rate that is:
A. Independent of the concentration of reactants
B. Directly proportional to concentration
C. Inversely proportional to concentration
D. Proportional to the square of concentration
Answer: A. Independent of the concentration of reactants
Explanation: In a zero order reaction, rate = k, so it does not depend on reactant concentration.
8. The slowest step in a multistep reaction mechanism is called the:
A. Rate determining step
B. Elementary step
C. Transition step
D. Equilibrium step
Answer: A. Rate determining step
Explanation: The overall rate of a multistep reaction is governed by its slowest step, called the rate determining step.
9. Pseudo first order reactions appear to follow first order kinetics because:
A. One of the reactants is present in large excess
B. Both reactants have equal concentration
C. The reaction is catalyzed
D. Temperature remains constant
Answer: A. One of the reactants is present in large excess
Explanation: When one reactant (e.g. water in hydrolysis) is in large excess, its concentration stays effectively constant, making the reaction appear first order.
10. According to collision theory, the rate of a reaction depends mainly on:
A. The frequency of effective collisions between reactant molecules
B. The total number of collisions only
C. The molecular mass of reactants
D. The number of moles present only
Answer: A. The frequency of effective collisions between reactant molecules
Explanation: Only collisions with proper orientation and sufficient energy (effective collisions) lead to product formation.
11. If the rate of a reaction doubles when the concentration of a reactant is doubled, the order with respect to that reactant is:
A. 1
B. 2
C. 0
D. 3
Answer: A. 1
Explanation: Rate ∝ [A]ⁿ; doubling [A] doubles the rate only when n = 1.
12. A catalyst increases the rate of a reaction mainly by:
A. Providing an alternate pathway with lower activation energy
B. Increasing the activation energy
C. Changing the equilibrium constant
D. Increasing the enthalpy of reaction
Answer: A. Providing an alternate pathway with lower activation energy
Explanation: Catalysts lower the activation energy barrier, allowing more molecules to react per unit time, without altering the equilibrium position.
