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AP Chemistry: Kinetics, Thermochemistry and Electrochemistry — quiz

15 multiple-choice questions covering Rate Laws, Reaction Mechanisms, Activation Energy & Catalysts, Enthalpy & Calorimetry, Hess's Law. One answer each; you get a score at the end and the explanation for every question. No account needed.

Updated 2026-11-04. Keys 1–4 pick an answer, Enter moves on. Redo it any time, in order or shuffled.

The questions

Answers and explanations are shown after you finish.

1. Rate Laws

   In a kinetics experiment, doubling the concentration of reactant A (while B is held constant) causes the reaction rate to increase by a factor of 4. What is the order of the reaction with respect to A?

   • 1
   • 2
   • 4
   • 0
2. Rate Laws

   Which statement correctly describes a reaction that is found to be zero order overall?

   • The rate remains constant as reactant concentration decreases, and k has units of mol·L⁻¹·s⁻¹
   • The half-life is independent of initial concentration
   • A plot of ln[A] vs. time gives a straight line
   • The rate is proportional to reactant concentration, and k has units of s⁻¹
3. Rate Laws

   A first-order reaction has a half-life of 20 seconds. How long will it take for the concentration to decrease from 0.80 M to 0.20 M?

   • 40 s
   • 10 s
   • 80 s
   • 20 s
4. Rate Laws

   A reaction's rate constant k has units of L·mol⁻¹·s⁻¹. What does this tell you about the reaction, and what plot would confirm it?

   • Second order; a plot of 1/[A] vs. time is linear
   • First order; a plot of [A] vs. time is linear
   • Zero order; a plot of [A] vs. time is linear
   • First order; a plot of ln[A] vs. time is linear
5. Reaction Mechanisms

   In a multistep reaction mechanism, why does the slowest elementary step control the overall reaction rate?

   • It always occurs first in the mechanism
   • It acts as a bottleneck limiting how fast products can ultimately form
   • It consumes the most reactant mass
   • It has the lowest activation energy among all steps
6. Reaction Mechanisms

   A mechanism has Step 1 (fast, reversible): A + B ⇌ X, and Step 2 (slow): X + C → D. Why can't the overall rate law simply be written as rate = k[X][C]?

   • Because fast steps never contribute to the rate law in any way
   • Because X is an intermediate, so its concentration must be expressed using the fast equilibrium from Step 1
   • Because rate laws can only be written using the overall reaction's stoichiometry
   • Because intermediates never appear in rate laws under any circumstances
7. Activation Energy & Catalysts

   According to the Arrhenius equation, which combination of changes would increase the rate constant k the most?

   • Increasing activation energy while keeping T constant
   • Decreasing temperature and increasing activation energy
   • Keeping T and Ea constant but decreasing the frequency factor A
   • Increasing temperature and decreasing activation energy
8. Activation Energy & Catalysts

   A catalyst speeds up a reaction by providing an alternate mechanism. Which quantity remains unchanged as a result?

   • The reaction mechanism
   • The activation energy of the forward reaction
   • The rate of the forward reaction only
   • The overall enthalpy change (ΔH) and the equilibrium constant (K)
9. Enthalpy & Calorimetry

   A 25.0 g sample of water absorbs 1045 J of heat (c = 4.18 J/g·°C). What is the resulting temperature change?

   • 10.0 °C
   • 5.0 °C
   • 15.0 °C
   • 25.0 °C
10. Hess's Law

    Reaction 1 (A → B) has ΔH₁ = +50 kJ. If the target Hess's law pathway requires the reverse reaction (B → A) multiplied by 2, what is the correctly adjusted enthalpy value to use?

    • +50 kJ
    • −100 kJ
    • +100 kJ
    • −50 kJ
11. Hess's Law

    Which statement correctly describes how standard enthalpies of formation are combined to calculate ΔH°rxn?

    • Add all ΔHf values together regardless of which side they're on
    • Sum product ΔHf values minus reactant ΔHf values, each multiplied by stoichiometric coefficients
    • Average the ΔHf values of all species in the reaction
    • Sum the reactant ΔHf values and subtract the product ΔHf values
12. Entropy

    Which of the following processes would most likely have a positive ΔS?

    • A liquid freezing into a solid
    • A gas condensing into a liquid
    • Two gas molecules combining into one gas molecule
    • A solid dissolving into solution, increasing the number of free particles
13. Gibbs Free Energy

    A reaction has ΔH > 0 and ΔS > 0. Under what temperature condition will this reaction be spontaneous?

    • Only at high temperatures
    • At all temperatures
    • Never spontaneous regardless of temperature
    • Only at low temperatures
14. Gibbs Free Energy & Electrochemistry

    A redox reaction has a very large equilibrium constant (K >> 1). What does this imply about ΔG° and E°cell for the reaction?

    • ΔG° is very negative and E°cell is positive
    • ΔG° is zero and E°cell is zero
    • ΔG° is very positive and E°cell is negative
    • ΔG° is negative but E°cell is also negative
15. Faraday's Law

    Using Faraday's law, how many moles of electrons are transferred when a current of 3.00 A flows for 643 seconds?

    • 0.0100 mol
    • 0.0200 mol
    • 0.0400 mol
    • 0.0300 mol