Notes #7
Chapter 18.1
Rate of a Chemical Change
Rate is the measure of the amount of
something changing in a given interval of
time.
In this case:
The amount of reactant changing per unit
time.
Example:
Rates of chemical reactions: are often measured
as a change in the number of moles during an
interval of time.
Collision Theory

When atoms, ions, or molecules collide
with enough kinetic energy, they are
able to form products.

The MORE they collide, the more the
product will form.
Activation Energy

The minimum energy that colliding particles must
have in order to react is called the activation
energy.
There are 4 factors that influence
the reaction rate:

1) Temperature: An increase in
temperature increases collisions to allow
reaction rate to increase.
Storing foods in a
refrigerator keeps them
fresh longer. Low
temperatures slow
microbial action.
There are 4 factors that influence
the reaction rate:

2) Concentration: higher concentration,
more collisions causing an increase
reaction rate.

In a room: the more crowded it is, the more you will bump
into people.


a. In air, a lighted splint glows and soon goes out.
b. When placed in pure oxygen (higher oxygen concentration), the
splint bursts into flame.
There are 4 factors that influence
the reaction rate:

Particle Size: the more surface area a
substance has, the more collisions
occur, and the faster it will react.

Pile of little sticks vs Large log

Ways to increase surface area:
 Smaller pieces: crushing or mashing
 Dissolving into solution
There are 4 factors that influence
the reaction rate:

4) Catalysts: lowers activation energy. Is
a substance added to a reaction that
increases reaction rate without being
used up.
Inhibitors

An inhibitor is a substance that
interferes with the action of a catalyst.
Preservatives
 Antioxidants and antimicrobials used in
drying fruits and preserving fruit juices
slow the action of microbes and limit
contact with air.

Question:

Why is it good practice to keep food in
closed containers?

Iodine Clock Reaction
 http://www.teachertube.com/video/iodine-
clock-set-to-willtellov-10434
Section 18.2
Reversible
Reactions and
Equilibrium
Chemical Equilibrium

At chemical equilibrium, no net change occurs
in the actual amounts of the components of
the system.
If the rate of the shoppers going
up the escalator is equal to the
rate of the shoppers going down,
then the number of shoppers on
each floor remains constant, and
there is an equilibrium.
Chemical Equilibrium
SO2 and O2
react to
give SO3
SO3
decomposes
to SO2 and
O2
At equilibrium, all three types of molecules are present.
Chemical Equilibrium

When the rates of the forward and reverse
reactions are equal, the reaction has
reached a state of balance called chemical
equilibrium.
Factors Affecting Equilibrium:
Le Châtelier’s Principle

If a stress is applied to a system in dynamic
equilibrium, the system changes in a way that
relieves the stress.

3 Types of Stresses:
 1) Changes in concentration of reactants or
products
 2) Changes in Temperature
 3) Change in Pressure
Stress 1: Concentration
(Of reactants OR products)

See example on board with Mrs. B
Stress 2: Temperature

Dinitrogen tetroxide is a colorless gas;
nitrogen dioxide is a brown gas. The
flask on the left is in a dish of hot water;
the flask on the right is in ice.
Stress 3: Pressure
Practice
Next Week:

Reaction Rates Lab
 Wear closed toes shoes. No back packs in
lab.

Equilibrium Constants and Solubility
Equilibrium
Classwork Due Today
Page 555 # 6
 Page 547 #1 ,2, 3, 5
