AP Chemistry Quiz: Introduction To Rate Law
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Introduction To Rate LawQuestion 1 of 20

Consider the reaction A→ProductsA \rightarrow Products. The initial rate of reaction is measured at different initial concentrations of A. When the initial concentration of A is doubled from 0.10 M to 0.20 M, the initial rate of reaction also doubles.

Based on this information, what is the order of the reaction with respect to reactant A?

Zero order
First order
Second order
Third order
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AP Chemistry Quiz

AP Chemistry Quiz: Introduction To Rate Law

Practice Introduction To Rate Law in AP Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Introduction To Rate Law, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Chemistry.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

Consider the reaction A→ProductsA \rightarrow Products. The initial rate of reaction is measured at different initial concentrations of A. When the initial concentration of A is doubled from 0.10 M to 0.20 M, the initial rate of reaction also doubles.

Based on this information, what is the order of the reaction with respect to reactant A?

  1. Zero order
  2. First order (correct answer)
  3. Second order
  4. Third order

Explanation: The correct answer is B. The rate law is Rate = k[A]xk[A]^x. When [A] is doubled, the new rate is k(2[A])x=2x(k[A]x)k(2[A])^x = 2^x(k[A]^x). The problem states that the rate doubles, so 2x=22^x = 2, which means x=1x = 1. The reaction is first order with respect to A.

Question 2

A chemical reaction is described by the rate law: Rate = k[X][Y]2k[X][Y]^2. If the concentration of X is tripled and the concentration of Y is doubled, the initial reaction rate will increase by a factor of

  1. 6
  2. 9
  3. 12 (correct answer)
  4. 18

Explanation: The correct answer is C. The change in rate is determined by the product of the concentration changes raised to their respective orders. The change will be (3)1×(2)2=3×4=12(3)^1 \times (2)^2 = 3 \times 4 = 12. The rate increases by a factor of 12.

Question 3

The value of the rate constant, k, for a specific chemical reaction is primarily dependent on which of the following factors?

  1. The initial concentration of the reactants.
  2. The pressure of gaseous reactants.
  3. The temperature of the reaction system. (correct answer)
  4. The time elapsed since the start of the reaction.

Explanation: The rate constant, k, is constant for a given reaction at a fixed temperature. Its value changes significantly with temperature, as described by the Arrhenius equation. The presence of a catalyst also changes k, but temperature is the primary factor listed. Concentrations and time do not affect the value of k.

Question 4

The balanced equation for the synthesis of ammonia is N2(g)+3H2(g)→2NH3(g)N_2(g) + 3H_2(g) \rightarrow 2NH_3(g). A student proposes that the rate law for this reaction is Rate = k[N2][H2]3k[N_2][H_2]^3. This proposed rate law is

  1. definitely correct, because the exponents in the rate law must match the stoichiometric coefficients.
  2. definitely incorrect, because reaction orders cannot be greater than two for any reactant.
  3. possibly correct, but it cannot be confirmed without evidence from experimental data. (correct answer)
  4. definitely incorrect, because the concentration of the product, NH₃, must be included in the rate law.

Explanation: The correct answer is C. Rate laws must be determined experimentally. They depend on the reaction mechanism, not the overall stoichiometry. While it is possible for the orders to match the coefficients (if the reaction is an elementary step), this cannot be assumed. Choice A is a common misconception. Choice B is false, as orders can be integers, fractions, or zero. Choice D is incorrect as product concentrations do not appear in the forward rate law.

Question 5

The reaction X+2Y→ProductsX + 2Y \rightarrow Products is studied, and the following initial rate data are collected. Experiment 1: [X]0=0.10M[X]_0 = 0.10 M, [Y]0=0.10M[Y]_0 = 0.10 M, Initial Rate = 0.0050M/s0.0050 M/s Experiment 2: [X]0=0.20M[X]_0 = 0.20 M, [Y]0=0.10M[Y]_0 = 0.10 M, Initial Rate = 0.0200M/s0.0200 M/s Experiment 3: [X]0=0.20M[X]_0 = 0.20 M, [Y]0=0.20M[Y]_0 = 0.20 M, Initial Rate = 0.0200M/s0.0200 M/s

What is the correct rate law for this reaction based on the data?

  1. Rate = k[X]2k[X]^2 (correct answer)
  2. Rate = k[X][Y]k[X][Y]
  3. Rate = k[X][Y]2k[X][Y]^2
  4. Rate = k[X]2[Y]k[X]^2[Y]

Explanation: To find the order for X, compare Experiments 1 and 2 where [Y] is constant. [X] doubles (0.20/0.10=20.20/0.10 = 2), and the rate quadruples (0.0200/0.0050=40.0200/0.0050 = 4). Since 22=42^2 = 4, the reaction is second order in X. To find the order for Y, compare Experiments 2 and 3 where [X] is constant. [Y] doubles (0.20/0.10=20.20/0.10 = 2), and the rate is unchanged (0.0200/0.0200=10.0200/0.0200 = 1). Since 20=12^0 = 1, the reaction is zero order in Y. The rate law is Rate = k[X]2[Y]0k[X]^2[Y]^0 or Rate = k[X]2k[X]^2.

Question 6

For the reaction X+Y→ZX + Y \rightarrow Z, the experimentally determined rate law is Rate = k[X]2k[X]^2.

An experiment is performed with [X]=0.40M[X] = 0.40 M and [Y]=0.40M[Y] = 0.40 M. A second experiment is performed with [X]=0.40M[X] = 0.40 M and [Y]=0.80M[Y] = 0.80 M. How will the initial rate of the second experiment compare to the first?

  1. The initial rate will be the same. (correct answer)
  2. The initial rate will be doubled.
  3. The initial rate will be halved.
  4. The initial rate will be quadrupled.

Explanation: The rate law, Rate = k[X]2k[X]^2, shows that the reaction is second order in X and zero order in Y. Since the rate does not depend on the concentration of Y, doubling [Y] while keeping [X] constant will have no effect on the initial rate. Therefore, the rate will be the same in both experiments.

Question 7

Consider the reaction: F2(g)+2ClO2(g)→2FClO2(g)F_2(g) + 2ClO_2(g) \rightarrow 2FClO_2(g). Based on initial rates experiments, the rate law was determined to be Rate = k[F2][ClO2]k[F_2][ClO_2].

Which statement accurately describes the relationship between the balanced chemical equation and the experimentally determined rate law for this reaction?

  1. The reaction orders for both reactants are identical to their stoichiometric coefficients, as is expected for all reactions.
  2. The stoichiometric coefficient for F2F_2 is 1, which is why its reaction order is 1; this direct correlation always holds.
  3. The rate law exponents must always be different from the coefficients to account for the reaction mechanism.
  4. The reaction order with respect to ClO2ClO_2 is 1, which is different from its stoichiometric coefficient of 2, demonstrating that orders must be found experimentally. (correct answer)

Explanation: This example highlights the key principle that reaction orders are not necessarily equal to the stoichiometric coefficients. Here, the order for F2F_2 happens to match its coefficient (both are 1), but the order for ClO2ClO_2 is 1 while its coefficient is 2. This shows that rate laws must be determined from experimental data, not from the balanced equation.

Question 8

A reaction follows the rate law: Rate = k[A]k[A]. The rate constant, k, is determined to be 4.0×10−3s−14.0 \times 10^{-3} \text{s}^{-1}.

If the initial concentration of A is 0.20M0.20 M, what is the initial rate of the reaction?

  1. 2.0×10−2mol L−1s−12.0 \times 10^{-2} \text{mol L}^{-1} \text{s}^{-1}
  2. 8.0×10−4mol L−1s−18.0 \times 10^{-4} \text{mol L}^{-1} \text{s}^{-1} (correct answer)
  3. 4.0×10−3mol L−1s−14.0 \times 10^{-3} \text{mol L}^{-1} \text{s}^{-1}
  4. 1.2×10−3mol L−1s−11.2 \times 10^{-3} \text{mol L}^{-1} \text{s}^{-1}

Explanation: The initial rate can be calculated by substituting the given values into the rate law equation: Rate = k[A]k[A]. Rate = (4.0×10−3s−1)(0.20mol L−1)=8.0×10−4mol L−1s−1(4.0 \times 10^{-3} \text{s}^{-1})(0.20 \text{mol L}^{-1}) = 8.0 \times 10^{-4} \text{mol L}^{-1} \text{s}^{-1}.

Question 9

The reaction NO2(g)+CO(g)→NO(g)+CO2(g)NO_2(g) + CO(g) \rightarrow NO(g) + CO_2(g) is studied at a certain temperature and the experimental rate law is found to be Rate = k[NO2]2k[NO_2]^2.

Which of the following statements correctly describes the reaction based on this rate law?

  1. The reaction is first order with respect to NO2NO_2 and first order with respect to CO.
  2. The reaction is second order with respect to NO2NO_2 and zero order with respect to CO. (correct answer)
  3. The reaction order must be equal to the stoichiometric coefficients, making it second order in NO2NO_2 and first in CO.
  4. The overall reaction order is 1, because CO is a reactant but does not appear in the rate law.

Explanation: The rate law explicitly shows the dependence of the rate on reactant concentrations. The exponent for [NO2][NO_2] is 2, so the reaction is second order with respect to NO2NO_2. Because CO is a reactant but does not appear in the rate law, its exponent is 0, meaning the reaction is zero order with respect to CO.

Question 10

The rate law for the decomposition of dinitrogen pentoxide is Rate = k[N2O5]k[N_2O_5].

If the initial rate of decomposition is measured to be RR at a certain initial concentration of N2O5N_2O_5, what will the initial rate be if the concentration of N2O5N_2O_5 is tripled?

  1. R/3R/3
  2. RR
  3. 3R3R (correct answer)
  4. 9R9R

Explanation: The reaction is first order with respect to N2O5N_2O_5, as indicated by the exponent of 1 on [N2O5][N_2O_5] in the rate law. In a first-order reaction, the rate is directly proportional to the concentration of the reactant. Therefore, if the concentration of N2O5N_2O_5 is tripled, the rate will also triple, becoming 3R3R.

Question 11

For a reaction that is found to be third order overall, which of the following are the correct units for the rate constant, k?

  1. mol L−1s−1\text{mol L}^{-1} \text{s}^{-1}
  2. s−1\text{s}^{-1}
  3. Lmol−1s−1L \text{mol}^{-1} \text{s}^{-1}
  4. L2mol−2s−1L^2 \text{mol}^{-2} \text{s}^{-1} (correct answer)

Explanation: The units of k can be derived from the general rate law. For a third-order reaction, Rate = k[concentration]3k[concentration]^3. Rearranging for k gives k=Rate/[concentration]3k = \text{Rate} / [concentration]^3. Substituting units: (mol L−1s−1)/(mol L−1)3=(mol L−1s−1)/(mol3L−3)=L2mol−2s−1(\text{mol L}^{-1} \text{s}^{-1}) / (\text{mol L}^{-1})^3 = (\text{mol L}^{-1} \text{s}^{-1}) / (\text{mol}^3 \text{L}^{-3}) = L^2 \text{mol}^{-2} \text{s}^{-1}.

Question 12

The rate law for a chemical reaction provides a mathematical relationship between the rate of reaction and which of the following?

  1. The concentrations of the products and the temperature.
  2. The temperature and the presence of a catalyst.
  3. The concentrations of the reactants. (correct answer)
  4. The stoichiometric coefficients of the balanced equation.

Explanation: The rate law expresses how the rate of a reaction depends on the concentration of the reactants. While temperature and catalysts affect the rate constant (k), the rate law itself is an expression in terms of reactant concentrations.

Question 13

The decomposition of nitrogen dioxide, 2NO2(g)→2NO(g)+O2(g)2NO_2(g) \rightarrow 2NO(g) + O_2(g), follows the rate law Rate = k[NO2]2k[NO_2]^2. If the rate is expressed in M s⁻¹, what are the units of the rate constant, kk?

  1. M s⁻¹
  2. M⁻¹ s⁻¹ (correct answer)
  3. s⁻¹
  4. M⁻² s⁻¹

Explanation: The correct answer is B. Rearranging the rate law gives kk = Rate / [NO2]2[NO_2]^2. Substituting the units gives (M s⁻¹) / M², which simplifies to M⁻¹ s⁻¹. Choice A represents the units of rate for a zero-order reaction, C represents the units for a first-order rate constant, and D represents the units for a third-order rate constant.

Question 14

A certain reaction is determined to be zero-order with respect to its single reactant, A. The rate law is Rate = kk. If concentration is measured in molarity (M) and time in seconds (s), what are the units for the rate constant, kk?

  1. M s⁻¹ (correct answer)
  2. s⁻¹
  3. M⁻¹ s⁻¹
  4. M⁻¹

Explanation: The correct answer is A. For a zero-order reaction, the rate is independent of reactant concentration (Rate = k[A]0k[A]^0 = kk). Therefore, the units of the rate constant kk must be the same as the units of the rate, which are M s⁻¹. Choice B represents units for a first-order rate constant, and C represents units for a second-order rate constant.

Question 15

For the reaction B→ProductsB \rightarrow Products, an experiment reveals that tripling the initial concentration of B causes the initial reaction rate to increase by a factor of nine.

What is the order of the reaction with respect to reactant B?

  1. Zero order
  2. First order
  3. Second order (correct answer)
  4. Third order

Explanation: The correct answer is C. The rate law is Rate = k[B]xk[B]^x. When [B] is tripled, the new rate is k(3[B])x=3x(k[B]x)k(3[B])^x = 3^x(k[B]^x). The problem states that the rate increases by a factor of nine, so 3x=93^x = 9, which means x=2x = 2. The reaction is second order with respect to B.

Question 16

In a study of the reaction C→ProductsC \rightarrow Products, the initial rate was measured as 2.0×10−42.0 \times 10^{-4} M/min when the initial concentration of C was 0.50 M. In a second trial, with an initial concentration of C of 1.0 M, the initial rate was found to be 2.0×10−42.0 \times 10^{-4} M/min.

Based on these data, the reaction is what order with respect to C?

  1. Zero order (correct answer)
  2. First order
  3. Second order
  4. The order cannot be determined from the data provided.

Explanation: The correct answer is A. Comparing the two trials, the initial concentration of C was doubled (from 0.50 M to 1.0 M), but the initial rate of the reaction remained unchanged. This indicates that the rate is independent of the concentration of C, which defines a zero-order reaction.

Question 17

The initial rate of the reaction X+Y→ZX + Y \rightarrow Z was measured in a series of experiments. Experiment 1: [X] = 0.1 M, [Y] = 0.1 M, Rate = 0.0200.020 M/s Experiment 2: [X] = 0.2 M, [Y] = 0.1 M, Rate = 0.0400.040 M/s Experiment 3: [X] = 0.1 M, [Y] = 0.2 M, Rate = 0.0800.080 M/s

Based on the data provided, what is the correct rate law for the reaction?

  1. Rate = k[X][Y]k[X][Y]
  2. Rate = k[X]2[Y]k[X]^2[Y]
  3. Rate = k[X][Y]2k[X][Y]^2 (correct answer)
  4. Rate = k[X]2[Y]2k[X]^2[Y]^2

Explanation: The correct answer is C. To find the order for X, compare experiments 1 and 2 where [Y] is constant. [X] doubles and the rate doubles, so the reaction is first order in X. To find the order for Y, compare experiments 1 and 3 where [X] is constant. [Y] doubles and the rate quadruples (0.080/0.020 = 4), so the reaction is second order in Y. The rate law is Rate = k[X][Y]2k[X][Y]^2.

Question 18

A reaction involves two reactants, P and Q. Experimental data shows the reaction is second-order with respect to P and zero-order with respect to Q.

What is the overall order of this reaction?

  1. 0
  2. 1
  3. 2 (correct answer)
  4. 3

Explanation: The correct answer is C. The overall reaction order is the sum of the individual orders of the reactants. In this case, the overall order is 2 (from P) + 0 (from Q) = 2.

Question 19

The reaction 2NO(g)+Cl2(g)→2NOCl(g)2NO(g) + Cl_2(g) \rightarrow 2NOCl(g) was studied at a certain temperature. The following initial rates were obtained from three experiments. Experiment 1: [NO] = 0.010 M, [Cl₂] = 0.010 M, Initial Rate = 1.8×10−51.8 \times 10^{-5} M/s Experiment 2: [NO] = 0.010 M, [Cl₂] = 0.020 M, Initial Rate = 3.6×10−53.6 \times 10^{-5} M/s Experiment 3: [NO] = 0.020 M, [Cl₂] = 0.020 M, Initial Rate = 1.44×10−41.44 \times 10^{-4} M/s

What is the correct rate law for this reaction?

  1. Rate = k[NO][Cl2]k[NO][Cl_2]
  2. Rate = k[NO][Cl2]2k[NO][Cl_2]^2
  3. Rate = k[NO]2[Cl2]k[NO]^2[Cl_2] (correct answer)
  4. Rate = k[NO]2[Cl2]2k[NO]^2[Cl_2]^2

Explanation: The correct answer is C. Comparing experiments 1 and 2, [NO] is constant while [Cl₂] doubles, and the rate doubles (3.6/1.8=23.6/1.8 = 2). Thus, the reaction is first-order in [Cl₂]. Comparing experiments 2 and 3, [Cl₂] is constant while [NO] doubles, and the rate quadruples (1.44×10−4/3.6×10−5=41.44 \times 10^{-4} / 3.6 \times 10^{-5} = 4). Thus, the reaction is second-order in [NO]. The rate law is Rate = k[NO]2[Cl2]k[NO]^2[Cl_2].

Question 20

For the reaction A+2B→C+DA + 2B \rightarrow C + D, the following initial rate data were collected. Experiment 1: [A] = 0.20 M, [B] = 0.10 M, Initial Rate = 5.0×10−35.0 \times 10^{-3} M/min Experiment 2: [A] = 0.40 M, [B] = 0.10 M, Initial Rate = 5.0×10−35.0 \times 10^{-3} M/min Experiment 3: [A] = 0.20 M, [B] = 0.20 M, Initial Rate = 2.0×10−22.0 \times 10^{-2} M/min

Which of the following is the rate law for this reaction?

  1. Rate = k[A]k[A]
  2. Rate = k[B]2k[B]^2 (correct answer)
  3. Rate = k[A][B]2k[A][B]^2
  4. Rate = k[A]0[B]1k[A]^0[B]^1

Explanation: The correct answer is B. Comparing experiments 1 and 2, [B] is constant while [A] doubles, and the rate remains unchanged. Therefore, the reaction is zero-order with respect to A. Comparing experiments 1 and 3, [A] is constant while [B] doubles, and the rate increases by a factor of 4 (2.0×10−2/5.0×10−3=42.0 \times 10^{-2} / 5.0 \times 10^{-3} = 4). Therefore, the reaction is second-order with respect to B. The rate law is Rate = k[A]0[B]2k[A]^0[B]^2, which simplifies to Rate = k[B]2k[B]^2.