This document discusses factors that affect the rate of chemical reactions and key concepts related to reaction rates. It covers how reaction rate depends on concentration, temperature, surface area, and catalysts. Catalysts lower the activation energy of a reaction, increasing the rate. Reaction rate can be determined from measurements of reactant disappearance or product appearance over time. The rate law equation describes the quantitative relationship between reaction rate and concentrations.

1. Chapter 16

2.  The time taken for the disappearance of the
reactant or the appearance of the product .
Rate is a ratio as the amount of reactant
disappeared divided by the time.
 Average rate: The change in the
concentration divided by the total time
elapsed.
 Rate = amount reacted or produced/ time
interval
 units: g/s, mol/s, or %/s

3. Instantaneous rate: rate measured
between very short interval
Initial rate: instantaneous rate at the
beginning of an experiment

4. Page 592
Concept check

5. Rate depends on the concentration:
In some reactions doubling the
concentration doubles the rate of reaction.
In some doubling the reaction increases
the reaction four folds.This happens in the
decomposition of HI to form H 2 and I2.

6. An expression for the rate of a reaction as
a function of the concentration of one or
more of the reactants.
Rate=k [A]n
This equation is the general rate law. The
exponent n , is called the order with
respect to substance A and must be
determined from experimental data.

7. Order of a chemical reaction can be said
as the exponent on the concentration for a
specified reactant in a rate law expression.

8. Determine the rate law equation for the
following reaction , given the experimental
data
3AC
Concentration of A Reaction rate
 0.2M 1.0M/s
 0.4M 4.0M/s

9. Page 596
Practice problems

10. The rate law equations you have looked so
far have been for reactions involving only
one reactant.
If more than one reactant is found to
contribute to the rate of the reaction, then
all contributing reactants must appear in
the rate law.
The rate law equation for this will be
rate=k [A] n [B] m

11.  The value of n is the order with respect to
reactant A. The value of m is the order with
respect to reactant B. The overall reaction
order will be the sum of n and m.
 From the above equation if you double the
concentration of A and the rate doubles then
the reaction is first order with respect to A. If
you double the conc. of B (keeping the conc
of A constant, and the rate quadruples the the
rate of the reaction is second order with
respect to B.

12. For the reaction A and B for this example
the rate law would be rate=k[A][B]2
Rate laws cannot be derived from a
chemical equation.
2N2O₅↔4NO2+O2
Keq=[NO2] 4 [O2]/[N2O₅]2
rate=k[N2O₅]1

13. The slowest step in a mechanism, the step
that determines the overall rate of reaction
is the rate determining step.
Mechanism is a proposed sequence of
steps that describes how reactants are
changed into products.
Each step in the mechanism is called as
elementary step.

14. Page 598
Critical thinking 2,3,5
Practice problems 7and 8 all

15.  Temperature: An increase in temperature is
accompanied by an increase in the reaction rate.
Temperature is a measure of the kinetic energy of
a system, so higher temperature means higher
average kinetic energy of molecules and more
collisions per unit time.
 For most chemical reactions the rate at which the
reaction proceeds will approximately double for
each 10°C increase in temperature. Once the
temperature reaches a certain point, some of the
chemical species may be altered (e.g., denaturing
of proteins) and the chemical reaction will slow or
stop.

16. Concentration: A higher concentration of
reactants leads to more effective collisions
per unit time, which leads to an increasing
reaction rate (except for zero order
reactions). Similarly, a higher concentration
of products tends to be associated with a
lower reaction rate.

17. Medium: The rate of a chemical reaction
depends on the medium in which the
reaction occurs. It sometimes could make
a difference whether a medium is aqueous
or organic; polar or nonpolar; or liquid,
solid, or gaseous.

18. Surface area: It is easier to dissolve sugar
if it is crushed. Crushing the sugar
increases its surface tension.The larger
surface area allows more sugar molecules
to contact the solution.

19.  Catalyst: A catalyst is a substance that alters
the rate of a chemical reaction without being
used up or permanently changed chemically.
 A catalyst works by changing the energy
pathway for a chemical reaction. It provides
an alternative route (mechanism) that lowers
the Activation Energy meaning more particles
now have the required energy needed to
undergo a successful collision.

20. What is activation energy?
The least amount of energy needed to
permit a particular chemical reaction.

21.  There are 2 types of catalysts:
 Homogeneous catalyst: Homogeneous
catalysts are in the same phase as the
reactants.
 Heterogeneous catalyst: Heterogeneous
catalysts are present in different phases from
the reactants (for example, a solid catalyst in
a liquid reaction mixture), whereas
homogeneous catalysts are in the same
phase (for example, a dissolved catalyst in a
liquid reaction mixture).

22. Example of Homogeneous catalyst
2H2O2(aq)+ KI(aq)2H2O(l)+O2(g)
Example of Heterogeneous catalyst
Decomposition of H2O2 in presence of MnO2
Hydrogen peroxide is a solution while
manganese dioxide is a solid and can be easily
separated.

23. Term review all
Page 614
13,22, 23 and 25
Test prep all