Kinetics Quiz
Questions: 16 · 10 minutes
1. What is the primary kinetic effect of a catalyst?
It increases the energy difference between reactants and products
It raises reactant concentrations during the reaction
It makes every molecular collision produce products
It provides an alternative pathway with lower activation energy
2. Consider this mechanism: Step 1: NO₂ + NO₂ → NO₃ + NO; Step 2: NO₃ + CO → NO₂ + CO₂. Which species is an intermediate?
NO₃, because it is produced in one step and consumed in the next
NO₂, because it is present as a reactant in the first step
CO, because it enters the mechanism during the second step
CO₂, because it remains among the overall products
3. A zero-order reaction begins with [A] = 0.80 M and has k = 0.10 M min⁻¹. What is [A] after 5.0 minutes?
0.08 M
0.30 M
0.50 M
0.18 M
4. A reaction has the rate law Rate = k[A][B]. During an experiment, B is present in such large excess that its concentration changes negligibly. What behavior is expected?
The reaction behaves as zero order because B is effectively constant
The observed rate is proportional to [A], giving pseudo-first-order behavior
The observed rate is proportional to [A]² because B is in excess
The rate constant k becomes equal to [B]
5. On a reaction-coordinate diagram, the reactants are at 40 kJ mol⁻¹, the transition-state peak is at 95 kJ mol⁻¹, and the products are at 20 kJ mol⁻¹. What is the forward activation energy?
55 kJ mol⁻¹
75 kJ mol⁻¹
20 kJ mol⁻¹
95 kJ mol⁻¹
6. A student plots concentration data from a reaction. Which straight-line graph supports first-order behavior in reactant A?
ln[A] against time, with a negative slope
[A] against time, with a positive slope
1/[A] against time, with a negative slope
Reaction rate against time, with zero slope
7. What are the usual units of the rate constant for an overall second-order reaction when concentration is measured in molarity and time in seconds?
Per second, written s⁻¹
Per molar per second, written M⁻¹ s⁻¹
Molar per second, written M s⁻¹
Per molar squared per second, written M⁻² s⁻¹
8. For a reaction involving NO and Br₂, doubling the NO concentration while keeping the Br₂ concentration constant quadruples the initial rate. Doubling the Br₂ concentration while keeping the NO concentration constant doubles the rate. Which dependence fits these results?
First order in NO and second order in Br₂
First order in both NO and Br₂
Second order in NO and zero order in Br₂
Second order in NO and first order in Br₂
9. What does the reaction rate describe?
The minimum concentration needed for a reaction to begin
The total energy released by a reaction at equilibrium
The proportion of reactants converted when equilibrium is reached
The change in a reactant or product concentration per unit time
10. A catalyst is added to a reversible reaction that has not yet reached equilibrium. What should happen under otherwise identical conditions?
The equilibrium shifts toward products because the forward reaction is accelerated
The equilibrium shifts toward reactants because the reverse reaction is accelerated
Equilibrium is reached sooner, but the equilibrium composition is unchanged
The equilibrium constant increases, producing a greater final product concentration
11. An elementary step is written as A + B → products. What is its molecularity?
Termolecular, because both reactants and products must be counted
Unimolecular, because the equation contains one reaction arrow
Bimolecular, because two reactant particles participate in the elementary event
Its molecularity cannot be assigned from an elementary-step equation
12. A reaction occurs in solution. The concentration of one reactant is doubled while temperature and all other conditions remain unchanged. Why might the reaction become faster?
Reactant particles collide more frequently per unit volume
Each collision releases twice as much energy
The reaction’s activation energy automatically becomes lower
The equilibrium constant increases with concentration
13. A first-order reaction has a rate constant of 0.231 min⁻¹. Approximately what is its half-life?
0.160 min
1.44 min
3.00 min
4.33 min
14. Initial-rate data are shown: Experiment 1 uses [A] = 0.10 M and [B] = 0.10 M, giving rate 2; Experiment 2 uses [A] = 0.20 M and [B] = 0.10 M, giving rate 4; Experiment 3 uses [A] = 0.10 M and [B] = 0.20 M, giving rate 8. What is the reaction order with respect to B?
Zero order
First order
Third order
Second order
15. A proposed mechanism is: Step 1: A + B → I (slow); Step 2: I + B → P (fast). If the first step controls the rate and is elementary, which concentration dependence does the mechanism predict?
The rate is proportional to the intermediate concentration multiplied by [B]
The rate is proportional to [A] multiplied by [B]
The rate is proportional only to [A]
The rate is proportional to [A] multiplied by the square of [B]
16. The same reaction mixture reacts faster at a higher temperature. According to collision theory and the Arrhenius model, what best explains this change?
The reaction enthalpy becomes more negative as particles move faster
The activation energy becomes zero at the higher temperature
A larger fraction of molecules has enough energy to overcome the activation barrier
Every collision at the higher temperature has the correct orientation