Q.1 Which of the following factors does NOT affect the rate of a chemical reaction?
Concentration of reactants
Temperature
Catalyst
Color of the container
Explanation - The rate of a reaction depends on reactant concentration, temperature, and catalysts. The color of the container has no effect.
Correct answer is: Color of the container
Q.2 The rate law for a reaction is given as Rate = k[A]^2[B]. What is the overall order of the reaction?
1
2
3
4
Explanation - The overall order is the sum of the powers of concentration terms: 2 (from [A]) + 1 (from [B]) = 3.
Correct answer is: 3
Q.3 For a first-order reaction, the time required for half of the reactant to react is called:
Mean life
Half-life
Reaction time
Equilibrium time
Explanation - In a first-order reaction, half-life is the time required for half of the reactant to disappear.
Correct answer is: Half-life
Q.4 Which of the following statements is true about zero-order reactions?
Rate depends on the square of concentration
Rate is independent of concentration
Rate depends linearly on concentration
Rate decreases with increasing temperature
Explanation - In a zero-order reaction, the rate is constant and does not depend on the concentration of reactants.
Correct answer is: Rate is independent of concentration
Q.5 The Arrhenius equation is expressed as:
k = Ae^(-Ea/RT)
k = Ae^(Ea/RT)
k = Ae^(RT/Ea)
k = Ae^(R/EaT)
Explanation - The Arrhenius equation relates the rate constant k to activation energy Ea, temperature T, and pre-exponential factor A.
Correct answer is: k = Ae^(-Ea/RT)
Q.6 The reaction rate increases with temperature because:
Reactants move slower at higher temperatures
Activation energy decreases
More molecules have energy greater than activation energy
Catalyst forms at higher temperature
Explanation - Higher temperature increases molecular kinetic energy, so more molecules can overcome the activation barrier, increasing the reaction rate.
Correct answer is: More molecules have energy greater than activation energy
Q.7 In a reaction following the rate law Rate = k[A][B]^2, doubling [B] while keeping [A] constant will:
Double the rate
Quadruple the rate
Halve the rate
No effect on the rate
Explanation - Rate depends on [B]^2, so doubling [B] increases the rate by 2^2 = 4 times.
Correct answer is: Quadruple the rate
Q.8 Which of the following is a pseudo-first-order reaction?
2A + B → C, with [B] >> [A]
A + B → C, with [A] = [B]
2A → B
A → B + C, catalyzed
Explanation - When [B] is in large excess, its concentration remains nearly constant, making the reaction effectively first-order with respect to [A].
Correct answer is: 2A + B → C, with [B] >> [A]
Q.9 For a first-order reaction, the concentration of reactant decreases exponentially with time. This implies the graph of ln[A] vs time is:
Linear with positive slope
Linear with negative slope
Curved upward
Curved downward
Explanation - For a first-order reaction, ln[A] = ln[A]0 - kt. Plotting ln[A] vs time gives a straight line with slope -k.
Correct answer is: Linear with negative slope
Q.10 The activation energy of a reaction can be determined experimentally by:
Measuring the half-life
Using the Arrhenius plot of ln k vs 1/T
Measuring equilibrium constant
Calculating molecular weight
Explanation - Plotting ln k against 1/T gives a straight line with slope -Ea/R, allowing determination of activation energy.
Correct answer is: Using the Arrhenius plot of ln k vs 1/T
Q.11 The reaction A → B follows first-order kinetics. If the rate constant k = 0.03 s^-1, the time required for 75% of A to react is:
23.1 s
46.2 s
69.3 s
92.4 s
Explanation - For first-order reaction: t = (0.693/k) × log2 fraction remaining; t_75% = 0.693/0.03 × log2(4) = 46.2 s approximately.
Correct answer is: 46.2 s
Q.12 Which statement about catalysts is FALSE?
They increase the rate of reaction
They lower the activation energy
They alter the reaction equilibrium
They remain chemically unchanged
Explanation - Catalysts speed up reactions by lowering activation energy but do not change the position of equilibrium.
Correct answer is: They alter the reaction equilibrium
Q.13 The order of reaction with respect to a reactant is determined experimentally and is:
Always equal to stoichiometric coefficient
The power to which concentration is raised in rate law
Always first order
Always zero order
Explanation - Reaction order is defined as the exponent of concentration of the reactant in the rate law, determined experimentally.
Correct answer is: The power to which concentration is raised in rate law
Q.14 The rate constant of a reaction doubles when the temperature is raised by 10°C. This rule is known as:
Arrhenius rule
Van’t Hoff rule
Collision theory
Empirical rule of thumb
Explanation - It is an empirical observation that for many reactions, the rate approximately doubles for every 10°C rise in temperature.
Correct answer is: Empirical rule of thumb
Q.15 The molecularity of an elementary reaction refers to:
Number of products formed
Number of reactant molecules involved
Overall reaction order
Number of steps in mechanism
Explanation - Molecularity is the number of molecules that collide in an elementary reaction to produce products.
Correct answer is: Number of reactant molecules involved
Q.16 Which of the following is an example of a bimolecular reaction?
A → B
2A → B
A + B → C
Both 2 and 3
Explanation - Bimolecular reactions involve two reactant molecules, either 2A or A + B.
Correct answer is: Both 2 and 3
Q.17 The integrated rate equation for a second-order reaction A → products is:
1/[A] = 1/[A]0 + kt
ln[A] = ln[A]0 - kt
[A] = [A]0 - kt
[A] = [A]0e^-kt
Explanation - For a second-order reaction, 1/[A] varies linearly with time with slope k.
Correct answer is: 1/[A] = 1/[A]0 + kt
Q.18 In the collision theory, the frequency factor 'A' in the Arrhenius equation represents:
Fraction of collisions with proper orientation
Total number of collisions per unit time
Activation energy
Temperature coefficient
Explanation - 'A' represents the number of collisions per unit time that have the correct orientation for reaction.
Correct answer is: Total number of collisions per unit time
Q.19 The reaction rate constant k has the unit L mol^-1 s^-1. The order of the reaction is:
0
1
2
3
Explanation - For second-order reactions, units of k = L mol^-1 s^-1.
Correct answer is: 2
Q.20 Which factor can convert a slow reaction into a fast reaction without changing temperature?
Increasing reactant concentration
Adding catalyst
Increasing volume
Decreasing pressure
Explanation - Catalysts speed up reactions by lowering activation energy without altering temperature.
Correct answer is: Adding catalyst
Q.21 The half-life of a first-order reaction is independent of:
Temperature
Rate constant
Initial concentration
Activation energy
Explanation - For a first-order reaction, t1/2 = 0.693/k, which is independent of the initial concentration.
Correct answer is: Initial concentration
Q.22 A reaction has rate law Rate = k[A]^m[B]^n. If the reaction is zero order in [A] and first order in [B], then m and n are:
m=0, n=1
m=1, n=0
m=1, n=1
m=0, n=0
Explanation - Zero order in [A] means m=0; first order in [B] means n=1.
Correct answer is: m=0, n=1
Q.23 If the rate constant of a reaction increases, the activation energy:
Increases
Decreases
Remains unchanged
Becomes zero
Explanation - A higher rate constant at the same temperature usually implies a lower activation energy, per Arrhenius equation.
Correct answer is: Decreases
Q.24 For a reaction A → B, the graph of 1/[A] vs time is linear. The reaction is:
Zero-order
First-order
Second-order
Third-order
Explanation - A linear plot of 1/[A] vs time indicates a second-order reaction.
Correct answer is: Second-order
Q.25 Which of the following is NOT a characteristic of a first-order reaction?
Half-life is independent of concentration
Rate is directly proportional to reactant concentration
Graph of ln[A] vs time is linear
Rate constant changes with concentration
Explanation - Rate constant k is independent of concentration for first-order reactions.
Correct answer is: Rate constant changes with concentration