1. Which of the following factors does NOT affect the rate of a reaction?
a) Catalyst
b) Temperature
c) Color of reactants
d) Concentration of reactants
Answer:
c) Color of reactants
Explanation:
The color of reactants has no direct influence on the rate of a reaction.
2. The rate of a reaction can be expressed in terms of:
a) Change in concentration of reactants per unit time
b) Amount of product formed
c) Time taken for completion of reaction
d) Both a and b
Answer:
d) Both a and b
Explanation:
The rate of a reaction can be given by the change in concentration of reactants or the amount of product formed over time.
3. The rate constant (k) of a reaction:
a) Increases with temperature
b) Decreases with temperature
c) Remains constant with temperature
d) Is independent of temperature
Answer:
a) Increases with temperature
Explanation:
Typically, the rate constant increases with temperature because as temperature rises, molecules move faster and collide more often.
4. A first-order reaction has a half-life of 10 minutes. How long will it take for 75% of the reactant to be consumed?
a) 10 minutes
b) 20 minutes
c) 30 minutes
d) 40 minutes
Answer:
b) 20 minutes
Explanation:
For a first-order reaction, the half-life remains constant. So, 50% is consumed in 10 minutes, and another 25% in the next 10 minutes. Hence, 20 minutes in total.
5. Activation energy is:
a) Energy required to start a reaction
b) Minimum energy required by reacting molecules to undergo effective collision
c) Maximum energy of the products
d) Average kinetic energy of the molecules
Answer:
b) Minimum energy required by reacting molecules to undergo effective collision
Explanation:
Activation energy is the threshold energy that molecules must possess for a reaction to proceed after collision.
6. Which of the following equations is known as the rate equation for the reaction: A + B → Products?
a) Rate = k
b) Rate = k[A]
c) Rate = k[A][B]
d) Rate = k[A]^2[B]
Answer:
c) Rate = k[A][B]
Explanation:
The rate of the reaction depends on the concentration of both reactants A and B.
7. A zero-order reaction:
a) Has a constant rate
b) Has a rate proportional to the concentration of reactant
c) Is independent of the concentration of the reactant
d) Both a and c
Answer:
d) Both a and c
Explanation:
The rate of a zero-order reaction remains constant and is independent of the concentration of the reactant.
8. For a reaction, if the concentration of reactants is doubled and the rate becomes eight times, the order of the reaction is:
a) 0
b) 1
c) 2
d) 3
Answer:
c) 2
Explanation:
If doubling the concentration increases the rate by a factor of 8, the reaction is second order.
9. The half-life of a second-order reaction is:
a) Directly proportional to the initial concentration
b) Inversely proportional to the initial concentration
c) Independent of the initial concentration
d) Proportional to the square root of the initial concentration
Answer:
b) Inversely proportional to the initial concentration
Explanation:
For a second-order reaction, half-life (t_1/2) = 1/(k[A]_0).
10. A reaction is first order in A and second order in B. If the concentration of B is tripled while A remains the same, the reaction rate will increase by:
a) 3 times
b) 6 times
c) 9 times
d) 12 times
Answer:
c) 9 times
Explanation:
Rate = k[A][B]^2. If [B] is tripled, the rate becomes 9 times the initial rate.
11. Which graph represents a zero-order reaction?
a) Concentration vs. Time
b) Time vs. Rate
c) ln(Concentration) vs. Time
d) 1/Concentration vs. Time
Answer:
a) Concentration vs. Time
Explanation:
A linear decrease in concentration with time indicates a zero-order reaction.
12. The Arrhenius equation is given by:
a) k = Ae^(-Ea/RT)
b) k = A + e^(-Ea/RT)
c) k = A^2 – e^(Ea/RT)
d) k = Ae^(Ea/RT)
Answer:
a) k = Ae^(-Ea/RT)
Explanation:
The Arrhenius equation relates the rate constant to the activation energy and temperature.
13. For a reaction with a negative rate constant, the reaction is:
a) Feasible
b) Not feasible
c) At equilibrium
d) Very fast
Answer:
b) Not feasible
Explanation:
A negative rate constant is not physically meaningful.
14. A catalyst affects the rate of reaction by:
a) Changing the activation energy
b) Altering the concentration of reactants
c) Modifying the temperature
d) Changing the equilibrium constant
Answer:
a) Changing the activation energy
Explanation:
A catalyst provides an alternate pathway with a lower activation energy.
15. The molecularity of a reaction is:
a) The sum of the stoichiometric coefficients of reactants
b) The number of molecules involved in the rate-determining step
c) The sum of molecules of reactants and products
d) The number of products formed
Answer:
b) The number of molecules involved in the rate-determining step
Explanation:
Molecularity is the number of molecules participating in an elementary reaction.
16. Which of the following units is correct for the rate constant of a zero-order reaction?
a) mol L^-1 s^-1
b) s^-1
c) L mol^-1 s^-1
d) mol^2 L^-2 s^-1
Answer:
a) mol L^-1 s^-1
Explanation:
The unit of the rate constant for a zero-order reaction is mol L^-1 s^-1.
17. In the reaction: 2A → B + C, the rate of appearance of B is:
a) Half the rate of disappearance of A
b) Twice the rate of disappearance of A
c) Same as the rate of disappearance of A
d) Four times the rate of disappearance of A
Answer:
a) Half the rate of disappearance of A
Explanation:
The stoichiometry dictates that 2 moles of A produce 1 mole of B.
18. If a reaction is third order with respect to a reactant, the rate of reaction will _____ if the concentration of that reactant is doubled.
a) Remain the same
b) Double
c) Quadruple
d) Increase by eight times
Answer:
d) Increase by eight times
Explanation:
For third-order reactions, if concentration is doubled, the rate increases by 2^3 = 8 times.
19. Which is NOT true for a first-order reaction?
a) Rate is directly proportional to the concentration of reactant
b) Half-life is independent of the initial concentration
c) Half-life decreases with an increase in initial concentration
d) The plot of ln(concentration) vs. time is a straight line
Answer:
c) Half-life decreases with an increase in initial concentration
Explanation:
For a first-order reaction, half-life is independent of the initial concentration.
20. Collision theory is based on the idea that:
a) Molecules must collide to react
b) Molecules collide and always react
c) Only some collisions lead to reaction
d) Collisions are not necessary for reactions
Answer:
c) Only some collisions lead to reaction
Explanation:
According to the collision theory, molecules must collide with the correct orientation and with energy equal to or greater than the activation energy for a reaction to occur.