Class Notes (835,929)
Canada (509,507)
HMB204H1 (23)
j (14)
Lecture

Chapter 14.doc

3 Pages
68 Views
Unlock Document

Department
Human Biology
Course
HMB204H1
Professor
j
Semester
Fall

Description
Chapter 14- Chemical Kinetics Nerosanth Selvarajah 14.1- The Rate of a Chemical Reaction • The rate of a reaction describes how fast the concentration of a reactant or product changes with time A + B  C + D Rate of Formation = ∆[C]/ ∆t Rate of Disappearance = -∆[A]/ ∆t • Rate of disappearance is a negative quantity because concentration decreases with time o The concentration at the end of a time period is less than t was at the start of the period 14.2 Measuring Reaction Rates • To determine rate of reaction, we need to measure changes in concentration over time • Reaction rate is not constant; the lower the remaining concentration of the reactant, the more slowly the reaction proceeds • Instantaneous Rate of Reaction- is the exact rate of a reaction at some precise point in the reaction. It is obtained from the slope of a tangent line to a concentration-time graph • Initial Rate of Reaction- is the rate of a reaction immediately after the reactants are brought together 14.3 Effect of Concentration on Reaction Rates: The Rate Law • Rate Law/ Rate Equation-for a reaction relates the reaction rate to the concentrations of the reactants m n Rate= k[A] [B] [Pg. 578] • Term order is related to the exponents in the rate law • The overall order of reaction is the sum of all the exponents: m + n + … • Rate constant (k)- is the proportionality constant in a rate law that permits the rate of a reaction to be related to the concentrations of the reactants o its values depend on the specific reaction, presence of a catalyst and temperature o the larger the value of k, the faster a reaction goes • order of the reaction establishes the general form of the rate law & the appropriate units of k • if reaction is first order in one of the reactants, doubling the initial concentration of that reactant causes the initial rate of reaction to double o zero order in reactant- no effect on initial rate of reaction o first order in reactant- initial rate of reaction doubles o second order in reactant- initial rate of reaction quadruples o third order in reactant- initial rate of reaction increases eightfold • order of reaction (indicated through rate law) establishes units of rate constant, k [k = M min -1 14.4 Zero-Order Reactions • zero-order reaction has a rate law in which the sum of the exponents, m + n+… is equal to 0 o reaction proceeds at a rate that is independent of reactant concentrations Rate of Reaction = k [A] = k = constant  concentration-time graph is a straight line with a negative slope  rate of reaction which is equal to k and remains constant throughout the reaction is the negative of the slope of the line  units of k are the same as units of rate of a reaction: mol/L*t = M/s • Integrated Rate Law- expresses the concentration of a reactant as a function of time [A]t= -kt + [A]o 14.5 First-Order Reactions  First-order reaction has a rate law in which sum of the exponents, m + n + …is equal to 1 ln ([A]t/ [A]o) = -kt or ln [A]t= -kt + ln[A] o  an easy test for a first-order reaction is to plot the natural logarithm of a reactant concentration versus time & see if graph is linear k = -slope  Half-Life of a reaction is the time required for one-half of a reactant to be consumed; time during which the amount of reactant or its concentration decreases to one-half of its initial value t1/2= ln 2 / k  Half-life is constant for a first-order reaction; it is also independent of the initial concentration used  In Reactions involving gases, Rates are often measured in terms of gas pressure  Radioactive decay is a first-order process 14.6 Second-Order Reactions Equation of Straight Line Graph: 1/ [A]t= kt + 1/[A] 0  Half life depends on both the rate constant & the initial concentration [A] 0 o Half –life is not a constant; its value depends on the concentration of reactant at the start of each half-life interval  Because the starting concentration is always one-half that of the previous half-life, each successive half-life is twice as long as the one before it t1/2= 1/ k[A] 0  Pseudo-First-Order Reaction- a second-order reaction that is made to behave like a first-order reaction by holding one reactant concentration constant 14.7 Reaction Kinetics: A Summary REFER TO PAGE 589 14.8 Theoretical Models for Chemical Kinetics Collision Theory:  Colli30on Theory- the number of molecular collisions per unit time; typical collision frequency is of the order of 10 collisions/second  Only a fraction of the collisions among gaseous molecules lead to chemical reaction  Cannot expect every collision to result in a reaction  Activation Energy- a reactions minimum energy above the average kinetic energy that molecules must bring to their collisions for a chemical reaction to occur  Rate of a reaction wi
More Less

Related notes for HMB204H1

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit