Skip to main content
Ch.15 - Chemical Kinetics
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
Chapter 15, Problem 39b

What are the units of k for each type of reaction?
a. first-order reaction
b. second-order reaction
c. zero-order reaction

Verified step by step guidance
1
Identify the type of reaction: In this case, it's a second-order reaction.
Understand the rate law for a second-order reaction: The rate law for a second-order reaction can be expressed as \(rate = k[A]^2\) or \(rate = k[A][B]\), where [A] and [B] are the concentrations of the reactants.
Analyze the units of rate and concentration: The rate of reaction is typically measured in \(\text{mol L}^{-1} \text{s}^{-1}\), and concentration is measured in \(\text{mol L}^{-1}\).
Set up the equation to find the units of k: Using the rate law, substitute the units into the equation. For example, if the rate law is \(rate = k[A]^2\), then substituting the units gives \(\text{mol L}^{-1} \text{s}^{-1} = k(\text{mol L}^{-1})^2\).
Solve for the units of k: Rearrange the equation to isolate k, which results in the units of k being \(\text{L mol}^{-1} \text{s}^{-1}\) for a second-order reaction.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
43s
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reaction Order

Reaction order refers to the power to which the concentration of a reactant is raised in the rate law of a chemical reaction. It indicates how the rate of reaction depends on the concentration of reactants. For example, a second-order reaction means that the rate is proportional to the square of the concentration of one reactant or the product of the concentrations of two reactants.
Recommended video:
Guided course
00:36
Average Bond Order

Rate Constant (k)

The rate constant (k) is a proportionality factor in the rate law that relates the rate of a reaction to the concentrations of the reactants. Its units vary depending on the order of the reaction. For a second-order reaction, the units of k are typically expressed as M^-1 s^-1, indicating that the rate depends on the concentration squared.
Recommended video:
Guided course
01:14
Equilibrium Constant K

Units of Measurement in Chemistry

Units of measurement in chemistry are essential for quantifying concentrations, rates, and other properties. In the context of reaction kinetics, understanding how to derive the units of k based on the reaction order is crucial. For second-order reactions, the units of k reflect the need to balance the rate (M/s) with the concentration terms, leading to the specific units of M^-1 s^-1.
Recommended video:
Guided course
02:52
Units of Radiation Measurement
Related Practice
Textbook Question

This graph shows a plot of the rate of a reaction versus the concentration of the reactant.

a. What is the order of the reaction with respect to A?

480
views
Textbook Question

This graph shows a plot of the rate of a reaction versus the concentration of the reactant A for the reaction A → products. c. Write a rate law for the reaction including an estimate for the value of k.

1703
views
Textbook Question

A reaction in which A, B, and C react to form products is first order in A, second order in B, and zero order in C c. By what factor does the reaction rate change if [A] is doubled (and the other reactant concentrations are held constant)? d. By what factor does the reaction rate change if [B] is doubled (and the other reactant concentrations are held constant)? e. By what factor does the reaction rate change if [C] is doubled? f. By what factor does the reaction rate change if the concentrations of all three reactants are doubled?

858
views
Textbook Question

This graph shows a plot of the rate of a reaction versus the concentration of the reactant.

b. Make a rough sketch of a plot of [A] versus time

844
views
Textbook Question

A reaction in which A, B, and C react to form products is first order in A, second order in B, and zero order in C. b. What is the overall order of the reaction?

422
views
Textbook Question

This reaction is first order in N2O5: N2O5(g) → NO3(g) + NO2(g) The rate constant for the reaction at a certain temperature is 0.053/s. a. Calculate the rate of the reaction when [N2O5] = 0.055 M

531
views