Orders of Reaction and Concentration

Chapter 14: 3-4 Homework

Reading Preparation
WebLecture
Study Activity
Preparation work for chat
Online Quiz
Lab Instructions

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 14: Sections 3 and 4.

Study Notes

14.3 The reaction rate can be expressed as the change in concentration over time.
- The rate equation or rate law is given for each reactant separately: different reactants can have different rates. For reactant A of a reaction, rate δ[A]/δt = k[A], where k is the experimentally determined rate constant. For a general reaction aA + bB → xX, the rate is k[A]^m[B]ⁿ. The rate constant and exponents m and n must be experimentally determined.
- The order of a reaction for a particular reactant is the exponent, such as m above; the overall reaction order is the sum of exponents of the reactants m + n + ... + z.
- Units of the rate constant k vary with order: first (time^-1), second (L/mole*time), zeroth (mole/liter*time).
- The rate equation can be determined by examining the rate of change at different levels of concentration for each reactant.
  - If the rate is independent of any concentration change, the reaction is zeroth order for that reactant.
  - If the rate doubles when the concentration of a reactant doubles, the reaction is first order for that reactant.
  - If the rate quadruples as the concentration doubles (that is, it varies as the square of the change), then the reaction is second order.
  Once the rate equation is known, it can be used to determine the rate of a reaction overall.
14.4 Rate laws can be expressed as integrated rate equations, using calculus to integrate the rate laws. These are often graphed to show the relationship between the integrated expression and time as linear.

Key Formula

Order	Rate Law	Integrated Equation
Zero	$- \frac{Δ R}{Δ t} = k {[R]}^{0}$	${[R]}_{0} - {[R]}_{t} = kt$
First	$- \frac{Δ R}{Δ t} = k [R]$	$\ln \frac{{[R]}_{t}}{{[R]}_{0}} = - kt$
Second	$- \frac{Δ R}{Δ t} = k {[R]}^{2}$	$\frac{1}{{[R]}_{t}} - \frac{1}{{[R]}_{0}} = kt$
Concept	Equation	Notes
Half-life law	$t_{½} = \frac{0.693}{k}$	k: rate 0.693: -ln 1/2 = ln 2

We can do a quick graphical analysis as well. If we make three graphs, and plot [R], ln[R], and 1/[R] against time, the graph which gives us a straight line tells us what the reaction order is for the reactant R.

Web Lecture

Read the following weblecture before chat: How Concentrations Affect Rates

Study Activity

Videos for Chapter 14: The Rates of Chemical Reactions

Review the Videos at Thinkwell Video Lessons.

Under "Chemical Kinetics"
- Orders of Reactions
  - First-Order Reactions
  - Second-Order Reactions
  - A Kinetics Problem

Review the Videos at Thinkwell Video Lessons.

Under "Chemical Kinetics"
- Reaction Rates
  - An Introduction to Reaction Rates
  - Rate Laws: How the Reaction Rate Depends on Concentration
  - Determining the Form of a Rate Law

Use the Rates of Reactions Simulation Rates of Reactions Simulation to explore Multiple Collisions.

Accept the default initial scenario.
- Pump A and BC molecules into the container.
- Raise the temprature until the total average energy is just below the peak potential energy. Do any reactions occur?
- Raise the temperature above the peak potential energy temperature. What happens?
Use the drop down menu under initial conditions to chose a different reaction. Vary the initial temperature and time how long it takes for the reaction to run to completion at higher or lower temperatures. How does temperature affect the reaction rate?

Chat Preparation Activities

Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

There is no chapter quiz YET.

(Aligns to) AP #11 GUIDED INQUIRY — Titration Methods — Phase I

Design an experiment that uses titration methods to determine the concentration of an unknown solution. You will need to analyze data from a oxidation-reduction (redox) reaction and determine solution concentrations for at least two different solutions.

Identify the equipment and materials you will need, the solutions you will analyze, and outline the steps you will follow to collect data.

Resources:

AP2009 11 Determination of appropriate indicators for various acid-base titrations pH determination
APGIE Investigation 8 Redox Titrations: How Can We Determine the Actual Percentage of H2O2 in a Drugstore Bottle of Hydrogen Peroxide?
HSCKM V-1 Determine the Effect of Concentration on pH and the pH Range of Indicators
HCSKM V-2 Determine the Molarity of Vinegar by Titration
IGHCE Lab 11.1 Concentration effects on pH
IGHCE Lab 11.2 pH in salt solutions

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Chemistry

Chemistry 14: 3-4