Questions about Rate Law and Rate Constant
Multiple-Choice Questions: Rate Law and Rate Constant
1. What does the rate law express?
A) The total mass of the products
B) The relationship between reaction rate and temperature
C) The relationship between reaction rate and reactant concentrations
D) The order of steps in a mechanism
E) The amount of catalyst used
2. What is the general form of a rate law for a reaction: A + B → C?
A) Rate = [A][B]/[C]
B) Rate = k[A]^m[B]^n
C) Rate = k[C]/[A]
D) Rate = [A] + [B]
E) Rate = [C]^m/[A]^n
3. What does the rate constant (k) depend on?
A) Concentration of products
B) Time
C) Temperature and nature of the reaction
D) Volume of the solution
E) Pressure only
4. In the rate law Rate = k[A]^2[B], what is the overall order of the reaction?
A) First order
B) Second order
C) Third order
D) Zero order
E) Cannot be determined
5. If doubling [A] causes the rate to quadruple, what is the order of the reaction with respect to A?
A) Zero
B) First
C) Second
D) Third
E) Fourth
6. Which of the following units could represent the rate constant (k) for a second-order reaction?
A) s⁻¹
B) mol·L⁻¹
C) mol·L⁻¹·s⁻¹
D) L·mol⁻¹·s⁻¹
E) mol²·L⁻²
7. What does a rate law NOT include?
A) Concentration of reactants
B) Reaction mechanism
C) Rate constant
D) Reaction order
E) Experimental data
8. If a reaction is zero-order with respect to [A], what happens to the rate when [A] is doubled?
A) Rate doubles
B) Rate triples
C) Rate increases fourfold
D) Rate is halved
E) Rate stays the same
9. Which method is used to determine the rate law of a reaction?
A) Titration curve
B) Spectroscopy
C) Experimental rate measurements
D) Stoichiometric coefficients
E) Theoretical predictions only
10. In Rate = k[A][B]^2, what is the order with respect to B?
A) Zero
B) First
C) Second
D) Third
E) Cannot be determined
11. What does the rate constant (k) indicate when the rate law is known?
A) How many molecules collide
B) The rate of reaction when all reactants are at unit concentration
C) The energy required to break bonds
D) The change in pressure
E) The number of products formed
12. What is the effect of increasing temperature on the rate constant (k)?
A) No effect
B) k decreases
C) k increases
D) k becomes zero
E) k changes only if pressure changes
13. Which of the following affects the value of the rate constant (k)?
A) Catalyst and temperature
B) Concentration of products
C) Surface area of the container
D) Color of the solution
E) Volume of solution
14. The rate law for a reaction is determined by:
A) The balanced chemical equation
B) The molecular formula
C) Experimental data
D) Thermodynamic stability
E) The number of products
15. In a first-order reaction, the rate is directly proportional to:
A) The square of the concentration
B) The inverse of concentration
C) The concentration of the reactant
D) The product concentration
E) The volume
16. What is the rate constant (k) for a zero-order reaction with units of mol·L⁻¹·s⁻¹?
A) It must be first-order
B) It means rate is independent of concentration
C) It depends on pressure
D) It increases with concentration
E) It is constant only at 0 °C
17. Which rate law expression is consistent with a reaction that is second-order overall?
A) Rate = k[A]
B) Rate = k[A]^2
C) Rate = k[A][B]
D) Both B and C
E) Both A and C
18. If a reaction is first-order in A and zero-order in B, the rate law is:
A) Rate = k[A]
B) Rate = k[B]
C) Rate = k[A][B]
D) Rate = k[A]^2[B]
E) Rate = k[B]^0[A]^1
19. What is the half-life expression for a first-order reaction?
A) t½ = [A]/k
B) t½ = 0.693/k
C) t½ = k/[A]
D) t½ = [A]^2/k
E) t½ = ln(2)/[A]
20. Which of the following best defines a rate-determining step?
A) The step with the most products
B) The fastest step in a mechanism
C) The step that defines the overall order of the reaction
D) The step with the fewest reactants
E) The step that releases the most energy
- Questions on Potential Energy
- Questions on Activation Energy and Activated Complex
- Questions about Catalysts
Answer Key with Explanations
1. C – The rate law relates reaction rate to the concentration of reactants.
2. B – The general form is Rate = k[A]^m[B]^n, where m and n are the orders.
3. C – The rate constant depends on temperature and the nature of the substances involved.
4. C – Adding the exponents: 2 (for A) + 1 (for B) = third order.
5. C – Rate quadrupling when [A] doubles implies a second-order dependence: 2² = 4.
6. D – The unit for a second-order rate constant is L·mol⁻¹·s⁻¹.
7. B – The rate law does not include the reaction mechanism, which must be inferred.
8. E – In zero-order, the rate is independent of the reactant's concentration.
9. C – Rate laws are found through experimental measurement of rate changes.
10. C – The exponent of B is 2, so the order with respect to B is second.
11. B – k gives the reaction rate when all reactants are at unit concentration.
12. C – As temperature increases, k generally increases due to higher molecular energy.
13. A – Catalysts and temperature affect the value of k.
14. C – The actual rate law must be determined by experimental data.
15. C – In a first-order reaction, rate is directly proportional to reactant concentration.
16. B – A zero-order reaction has a constant rate independent of concentration.
17. D – Both Rate = k[A]^2 and Rate = k[A][B] are second-order overall.
18. E – Zero order in B means [B]^0 = 1, so Rate = k[A]^1[B]^0.
19. B – For first-order reactions, t½ = 0.693/k.
20. C – The rate-determining step is the slowest step, often defining the reaction's rate law.
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