Reaction
Kinetics 1
Chapter 22
Objectives
Explain and use the terms rate equation, order of reaction, overall
01 order of reaction, and rate constant
Understand and use rate equations of the form rate = k[A]m[B]n (for
02 which m and n are 0,1 or 2)
03 Deduce the order of a reaction from concentration-time graphs or
from experimental data relating to the initial rates method.
04 Construct a rate equation.
05 Interpret experimental data in graphical form, including
concentration-time and rate-concentration graphs.
06 Calculate the numerical value of a rate constant using the initial
rates and the rate equation.
Rate of
A change in concentration of a particular
reactant or a product over a period of time.
Reaction
Rate The rate equation is an experimentally
determined equation that relates rate of
reaction to the concentration of substances
Equation
in the reaction mixture.
The rate constant is a constant of
proportionality relating the concentrations in
the experimentally determined rate equation
to the rate of a chemical reaction.
Rate
Equation
The rate equation can be determined only
from experimental data and not from the
chemical (stoichiometric) equation.
Order of Reaction
Order of the reaction with
The order of a reaction with respect to a respect to a particular
particular reactant is the power of the substance
reactant’s concentration in the
experimentally determined rate equation.
An overall order of reaction is the sum of the
powers of the concentration terms in the
experimentally determined rate equation. Sum of the powers is 1 + 2 = 3
Question #1a-c
Write rate equations for each of the following reactions:
Question #1a-c
Write rate equations for each of the following reactions:
Answers:
(a) rate = k[cyclopropane]
(b) rate = k[HI]2
(c) rate = k[C12H22O11] [H+]
Question #1d-e
Write rate equations for each of the following reactions:
Question #1d-e
Write rate equations for each of the following reactions:
Answers:
(d) rate = k[HgCl2] [K2C2O4]2
(e) rate = k[CH3COCH3] [H+]
Zero Order The rate of reaction is independent of the
concentration of the reactants in these
reactions.
A change in the concentration of the reactants
has no effect on the speed of the reaction.
The rate equation is equal to the rate
constant.
Slope = 0 Unit of rate constant = concentration time -1
(eg. mol dm-3s-1)
Zero Order
The rate of reaction is independent of the
concentration of the reactants in these
reactions.
A change in the concentration of the reactants
has no effect on the speed of the reaction.
The rate equation is equal to the rate
constant.
The constant rate is indicated by the graph of
concentration against time being a straight
line. A straight line has a constant gradient
and indicates that the rate does not change as
the concentration of {A] changes.
First Order
The rate of reaction is directly proportional to
the concentration.
First Order
The rate of reaction is directly
proportional to the concentration of
one of the reactants.
Rate = k[A]
Unit of rate constant = time -1
(eg. s-1)
Second Order
The rate of reaction is proportional to the
concentration squared.
The rate equation is rate = k[A]2
Unit of the rate constant = concentration -1
time -1 (eg. mol-1dm3s-1)
Second Order
The rate of reaction is proportional to the
concentration squared.
The rate equation is rate = k[A]2
Unit of the rate constant = concentration -1
time -1 (eg. mol-1dm-3s-1)
Question #2a
Nitrosyl chloride, NOCl, can be formed by the reaction between nitrogen monoxide
and chlorine, as shown. 2NO + Cl2 → 2NOCl
The initial rate of this reaction is investigated, starting with different concentrations
of NO and Cl2. The results obtained are shown in Table 5.1.
Use the data in Table 5.1 to deduce the rate equation for this reaction.
Explain your reasoning. [3]
Question #2a
Nitrosyl chloride, NOCl, can be formed by the reaction between nitrogen monoxide
and chlorine, as shown. 2NO + Cl2 → 2NOCl
Answer:
● The order of reaction with respect to [NO] using exp 1 and 2 is second order. The concentration of
NO increases 3x and the rate increases by 9.
● The order of reaction with respect to [Cl2] using exp 1 and 3 is first order. [NO] increased by 2, [Cl2]
increased by 4 and the rate increases by 16.
● Rate = k[NO]2[Cl2]
Question #2b
Use your rate equation from (a)(i) and the data from experiment 1 to calculate the
rate constant, k, for this reaction. Include the units of k.
● Rate = k[NO]2[Cl2]
Question #2b
Use your rate equation from (a)(i) and the data from experiment 1 to calculate the
rate constant, k, for this reaction. Include the units of k.
Answer:
Rate = k[NO]2[Cl2]
k = 3,925.33 dm6 mol–2 min–1
Question #3a
Question #3a
rate = k[A][B]
rate = k[A]2[B]0 or rate = k[A]2
rate = k[A]0[B]2 or rate = k[B]2
Question #3b
Choose one of the rate equations you have written in (i), and
calculate the value of the rate constant, k. Include the units of k.
Question #3b
Choose one of the rate equations you have written in (i), and
calculate the value of the rate constant, k. Include the units of k.
Answer:
rate = k[A][B]
k = 7.625 mol–1 dm3 s–1
