1. The rate of a chemical reaction doubles when its temperature is increased from 20°C to 40°C. What is the activation energy of the reaction?
Answer:
Explanation:
Using the Arrhenius equation and given data, the activation energy is calculated to be approximately 60 kJ/mol.
2. Which of the following will NOT affect the rate of a reaction?
Answer:
Explanation:
The color of reactants does not influence the rate of a chemical reaction.
3. For a reaction: 2A -> B + C. If the concentration of A is doubled, and the rate becomes 8 times, what is the order of the reaction with respect to A?
Answer:
Explanation:
Rate ∝ [A]^n. When [A] is doubled, rate becomes 8 times, indicating the reaction is second order with respect to A.
4. A zero-order reaction has a constant:
Answer:
Explanation:
For a zero-order reaction, the rate is independent of the concentration of the reactants.
5. The half-life of a first-order reaction is 10 minutes. How much time is required for 87.5% completion?
Answer:
Explanation:
For a first-order reaction, after 2 half-lives (20 minutes), 75% reaction is complete. 87.5% completion requires an additional half-life, totaling 30 minutes.
6. Which graph represents a first-order reaction?
Answer:
Explanation:
For a first-order reaction, the plot of ln(concentration of reactant) vs. time gives a straight line.
7. Collision theory is based on the concept of:
Answer:
Explanation:
For a reaction to occur, reactant molecules should collide with the correct orientation and sufficient energy.
8. A catalyst affects the:
Answer:
Explanation:
A catalyst provides an alternate pathway with a lower activation energy but does not affect the overall energy change or equilibrium constant.
9. Rate of disappearance of a reactant is __________ to the rate of appearance of a product.
Answer:
Explanation:
Rate of disappearance of a reactant is negative while rate of appearance of a product is positive, but their magnitudes are equal.
10. Units of rate constant for a zero-order reaction are:
Answer:
Explanation:
For a zero-order reaction, rate = k, so units of k are same as that of rate i.e., M/s.
11. An exothermic reaction with increasing entropy will have:
Answer:
Explanation:
For an exothermic reaction with increasing entropy, both ΔH and ΔS are negative, leading to ΔG < 0, making the reaction spontaneous.
12. In Arrhenius equation k = A e^(-Ea/RT), the term 'A' represents:
Answer:
Explanation:
'A' is the pre-exponential factor or frequency factor that represents the number of collisions occurring per unit time.
13. Which of the following statements about reaction mechanisms is FALSE?
Answer:
Explanation:
Reaction mechanisms may or may not include a slow step. Some reactions proceed without any discernable slow step.
14. The half-life of a reaction is independent of the initial concentration for:
Answer:
Explanation:
For first-order reactions, half-life is independent of the initial concentration.
15. The unit of activation energy is:
Answer:
Explanation:
Activation energy is an energy term and has units of energy per amount of substance, typically Joules per mole.
16. The activation energy for a reaction can be determined from the slope of which plot?
Answer:
Explanation:
According to the Arrhenius equation, plotting ln k against 1/T gives a straight line with slope related to the activation energy.
17. If the rate of reaction does not depend on the concentration of any reactant, the reaction is:
Answer:
Explanation:
A zero-order reaction has a rate that is independent of the concentration of the reactants.
18. A catalyst changes the:
Answer:
Explanation:
A catalyst provides an alternate pathway (with lower activation energy) and changes the speed, but not the equilibrium position of a reaction.
19. A reaction with a large rate constant is:
Answer:
Explanation:
A large rate constant generally indicates a faster reaction rate.
20. The temperature coefficient of a reaction is the factor by which its rate increases for every:
Answer:
Explanation:
The temperature coefficient typically represents the factor by which the rate of reaction increases for every 10°C rise in temperature.