1) Concentration change of a substance in a unit time is called reaction rate and shown as dC/dt.

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CHEMICAL KINETICS

Chemical kinetics is related with the speed of chemical reactions and the mechanics of reactions. Here are two basic concepts:

1) Concentration change of a substance in a unit time is called reaction rate and shown as dC/dt.

2) Reaction Mechanism: It is the order of the

reactions that go one step to the collective

change.

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THE FACTORS AFFECTING THE SPEED OF CHEMICAL REACTIONS

1) The Nature of the Reactive Substance

In a chemical reaction, the bonds between molecules are broken and new bonds are occured. Rate must be depend to special bondings that newly entering to the reaction.

Experimental reaction rate is depended to the

bringing together of definite substances in a

reaction.

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So the rate of reaction varies from substance to

substance. Some reactions are so fast that their

speed can not be measured (such as

sedimentation reactions and neutralization

reactions), and others are so slow that human life

can not be enough to measure the speed (such as

the combination of oxygen and hydrogen and

geological reactions).

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Concentration of reactive substances In heterogeneous reactions:

It covers more than one phase and the velocity is proportional to their contact surface. For example;

the corrosion of iron with oxygen increases as the surface increases.

In homogenous reactions:

It occurs in single phase and the reaction rate

depends on the concentration of the reactive

substances.

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Reaction rate is described as;

nA + mB  Product

Reaction rate = k [A]

ⁿ

[B]

^m

k: constant of reaction rate

n and m are empirically found exponential expressions. These can be negative or fractional, which indicates the inverse proportion.

n + m is called the order and indicates the degree of reaction.

Although the reaction rate depends on the concentration, the

reaction rate can not be calculated only by looking at the structure

of the molecules. The reaction rate is only found experimentally.

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Experimentally, there can be a dependence of the rate by determining either the increase in the concentration of the product or the decrease in the concentration of the starting substance.

For the rate of the reaction, what has been said so far is always over the initial concentration.

However, since the concentrations will change

continuously during the reaction, the reaction rate

will also change.