FACTORS AFFECTING THE RATES OF CHMICAL REACTION

Factors Affecting

the Rates of

Chemical
Reaction

Describe effective collision resulting in the
formation of products.

Determine the use of energy diagrams.
Describe the effect of the catalyst on the
activation energy and reaction rate
Determine the effects of temperature on the
reaction rate.

Learning Objectives

Have you ever watched children playing “Pukpok Palayok”? It is a fun game played
during Filipino fiestas and traditional parties. The player is blindfolded while holding
a stick. The player is told to walk in line toward where the pot or palayok is hanging.
The player will try to hit it. A hit on the “palayok” or pot with a stick could result in
breaking the pot, releasing a lot of items from it.

When the person holding the stick hits the pot, there is a release of new items
from the pot. The person holding the stick exerts energy on hitting the pot. The
impact of the stick on the pot is the collision. When the stick hits the pot, the pot
will break releasing items in it. Energy is needed to break the pot. This game is
close in illustrating the collision theory. To release the goods inside the pot, the
player must hit the pot, with sufficient energy.

states that atoms or molecules must
collide with enough energy in order to
react.

Collision Theory

The reactants in a chemical reaction must
also collide to form a new product. The
reactant molecules must come together in a
collision in order to react and produce
molecules.

When molecules collide, a certain
minimum energy called activation
energy is required for a reaction to
occur. This was suggested in 1888 by
Svante Arrhenius.

Activation energy is needed to break the bonds of
the reactants to form new products or new
substances.
In the diagram (Figure 3), you could see that the
reactants required an amount of energy in a
period of time to produce products. The activated
complex is located at the peak of the energy
diagram for a reaction.l

Why is there a need to chop a large firewood
into smaller pieces or to its desirable sizes
before using it to build a fire in a wood
stove? Smaller pieces of firewood burn
easily compared to large pieces of wood. If
we do not chop the wood, it will take more
time for the wood to burn. In barbequing,
large chunks of charcoal

In barbequing, large chunks of charcoal is
used to slowly cook the meat. The desired
temperature is to produce an ember that
will provide sustained heating, not fire.
Small chunks of charcoal produces fire
rather than the right amount of heat. When
solid reactants are present in small pieces,
reaction rates can increase. The smaller
pieces have a greater surface area, thus,
providing much greater contact among the
reactants and effecting more collisions.

Particle Size or Surface Area

When solid reactants are present in small pieces,
reaction rates can increase. The smaller pieces
have a greater surface area, thus, providing much
greater contact among the reactants and effecting
more collisions.

Another important factor influencing the frequency of
collision is concentration. Concentration is the
measure of the number of particles of solute
contained in each volume of solution. Corrosion is
another chemical change that happens all around us.
Corrosion results in the deterioration of the metal.
One of the most common forms of corrosion is the
rusting of iron metals when it is exposed to air and
moisture. It results in the formation of a red or
orange flakes on the surface of iron. These flakes
can be removed, exposing another layer of the metal
for rusting.

Concentration

In real life, we cannot see
molecules. We can feel its
presence by tasting, feeling
(skin and as eye irritation) and
smelling. Way to visualize
how particles are affected by
temperature.

Effect of Temperature on particles, as the
temperature rises, the molecules in hot water (b),
move faster and therefore collide more and have
greater chances to react with each other than in
the cold water (a). Increasing the temperature
increases the rate of reaction. Therefore, heating
allows more frequent collisions among particles.
Most frequent collisions will lead to sufficient
energy that will provide necessary activation
energy for the reaction to start.

Temperature

In food preservation, temperature
plays a big role in extending the shelf
life of foods. This is the reason why
perishable foods are chilled or frozen.
Decreasing the temperature lowers
the rate of spoilage items. Another
way to lengthen the shelf life of food
is drying. Drying lowers the moisture
or water content in food in order to
prevent the growth microorganism
like bacteria, yeast and molds.

The rate of chemical reactions
can be altered. The substance
that alters the rate or speed
of

chemical

reactions

is

called a catalyst. Generally,
a catalyst is used to speed up
a chemical reaction but there
are also catalysts that slows
down a reaction. These are
known as inhibitors.

One example of a chemical reaction
with a catalyst is the decomposition of
hydrogen peroxide (Agua Oxinada) to
produce oxygen gas and water with the
catalyst manganese (IV) oxide (MnO2).
Hydrogen peroxide (H2O2) (see Figure
7) is decomposed naturally and will
produce oxygen gas when left exposed
but will take a longer time. However,
when small amount of MnO2 is added,
bubbles can be seen immediately
signifying

that

there

is

reaction

happening. When lighted match is
placed near the mouth of the test tube,
it will be reignited.

Catalyst

A catalyst alters the speed of reaction by changing the
activation energy. Figure 8 shows a diagram how the enzyme
that acts as the catalyst speeds up a chemical reaction works
by decreasing the activation energy.

THANK YOU

Submitted by:

Stella Marie L. Amora

April Jade Aquino

Submitted to: Agnes T. Naingue