Factors Affecting the Rate

of Chemical Reactions

By Prof. Liwayway Memije-Cruz

Chemical Reaction

• a process in which one or more substances,

the reactants, are converted to one or more

different substances, the products.

Substances are either chemical elements or

compounds.

• rearranges the constituent atoms of the

reactants to create different substances as

products.

• an integral part of technology, of culture,

and indeed of life itself. Burning fuels,

smelting iron, making glass and pottery,

brewing beer, and making wine and cheese

are among many examples of activities

incorporating chemical reactions that have

been known and used for thousands of

years.

• Chemical reactions

abound in the

geology of Earth, in

the atmosphere and

oceans, and in a

vast array of

complicated

processes that occur

in all living

systems.

Rate of chemical reaction is the

speed at which a reaction proceeds.

Factors Affecting the Rate of

Chemical Reactions:

Factors Affecting the Rate of

Chemical Reactions:

How does chemical nature of

reactants affect the rate of a reaction?

• During chemical reactions, chemical bonds

are broken and new bonds are formed.

• The nature (or type) of these chemical bonds

- and how readily they are broken and

formed - plays a critical role in the rate of a

reaction. When the reaction involves

primarily the exchange of electrons ,

reactions tend to be very rapid.

Phase and Surface Area Effects

• The larger the

surface area, the

faster the rate of

reaction.

• A pile of flour is only scorched by a flame (right), but when the same flour is sprayed into the flame, it burns rapidly

How will increasing the concentration of

reactants affect the rate of a chemical reaction?

• It will increase the reaction rate

or leave it the same, depending

on whether the particular

reactant added is one that is

limiting the reaction rate before

the addition.

How does decreasing the concentration of the

reactants affect the rate of a chemical reaction?

• Decreasing the concentrations of

all the reactants will almost always

decrease the rate of the reaction.

Decreasing the concentration of

only reactants not involved in the

rate determining step will not

change the reaction rate at all.

What is the reactant affected by an

enzyme in a chemical reaction?

• substrate

• any substance upon which an enzyme

acts.

Concentration Effects

• Mixing sucrose with dilute sulfuric acid in a beaker (a, right) produces a simple solution. Mixing the same amount of sucrose with concentrated sulfuric acid (a, left) results in a dramatic reaction (b) that eventually produces a column of black porous graphite (c) and an intense smell of burning sugar.

How does the concentration of reactants

affect the rate of a reaction?

• Increasing the concentration

increases the molecules' collision

frequency.

• Increasing the concentration of the

reactants increases the rate of the

reaction.

Temperature

• sensation of warmth or

coldness felt from

contact with it.

• hotness and coldness

of an object.

• degree of sensible heat

or cold.

• expressed in terms of a

specific scale.

Temperature Scales

Temperature Effects

• An increase in

temperature usually

increases the rate of

reaction. As heat is

added, the average

kinetic and internal

energies of reacting

molecules increase so

the rate of reaction

increases too.

Catalyst

• a substance that participates in a

chemical reaction and increases

the reaction rate without

undergoing a net chemical change

itself.

Catalyst Effects

• A solution of hydrogen peroxide

(H2O2) decomposes in water so

slowly that the change is not

noticeable (left). Iodide ion acts as a

catalyst for the decomposition of

H2O2, producing oxygen gas. The

solution turns brown because of the

reaction of H2O2 with I−, which

generates small amounts of I3−

(center). The enzyme catalase is about

3 billion times more effective than

iodide as a catalyst. Even in the

presence of very small amounts of

enzyme, the decomposition is

vigorous (right).

References

• https://catalog.flatworldknowledge.co

m/bookhub/reader/1790?e=averill_1.0-

ch14_s01

• https://www.britannica.com/science/ch

emical-reaction

• http://www.answers.com/Q/What_caus

es_the_concentration_of_reactants_to_

affect_the_reaction_rate#slide=1