Rate Of Reaction

Chemical Kinetics of Class 12

The rate of a reaction means the speed with which the reaction takes place. This is expressed either in terms of decrease in the concentration of a reactant per unit time or increase in the concentration of a product per unit time.

Rate of reaction Rate Of Reaction

Or, Rate Of Reaction

The term Rate Of Reaction means Rate Of Reaction and  is the amount of time elapsed. For example, a car driver starts his journey at 9.00 AM with odometer reading x miles. At 11.00 AM, he reaches his destination. The odometer reading at destination is y miles. The rate of his travel can be calculated as

Rate Of Reaction

The above example indicates that the car has been driven with uniform rate but actually it has been driven sometimes faster and sometimes slower depending upon the condition of road. Thus, the overall rate is an average rate and the rate at which the car was moving at any instan

t, called instantaneous rate. The rate measured over a long time interval is called average rate and the rate measured for an infinitesimally small time interval is called instantaneous rate.

In general, for any reaction of the type

Rate Of Reaction

Average rate of reaction Rate Of Reaction

Where [A] signifies the molar conc. of (A) and Rate Of Reaction stands for the change in molar concentration of A. The negative sign placed before a reaction rate symbol signifies a decrease in concentration of the reactant with increase of time and a positive sign before the rate symbol signifies that the concentration of product increases with increase of time.

Average rate of reaction

The rate measured over a long time interval is called average rate. The rate of reaction (average rate) is defined as the change of concentration of any one of the reactants (or products) per unit time.

Average rate of reaction Rate Of Reaction

Consider the reaction between CO and Rate Of Reaction

Rate Of Reaction

This equation shows that one mole of CO reacts with one mole of Rate Of Reaction one mole each of Rate Of Reaction are formed. The average rate of reaction can be expressed either by decrease in conc. of reactant Rate Of Reaction or by the increase in conc. of any one of products Rate Of Reaction

Thus, Rate Of Reaction

For the reaction, Rate Of Reaction

When 2 moles of Rate Of Reaction decomposed, one mole of Rate Of Reaction and 2 moles of Rate Of Reaction is formed. The rate of increase in the conc. of Rate Of Reaction therefore is half that of the disappearance of the conc. of Rate Of Reaction and increase in conc. of Rate Of Reaction is the same of the disappearance of the conc. of Rate Of Reactionin the same time interval.

So Rate Of Reaction

In general, for a reaction, Rate Of Reaction

The rate is expressed as:

Rate Of Reaction

Instantaneous rate

With the progress of reaction the conc. of reactants decreases while that of product increases. According to law of mass action the rate of reaction decreases moment to moment as shown by graph of rate vs. time.

Rate varies from moment to moment so rate of reaction has to be specified at a given instant of time called instantaneous rate

Rate Of Reaction

Rate Of Reaction

Where dC is the infinitesimal change in conc. during infinitesimal time interval dt after time t i.e. between t and t + dt.

Consider a reactionRate Of Reaction,To know the rate of reaction at any time t, a tangent is drawn to curve at the point corresponding to that time and it is extended on either side so as to cut the axes, say at the point A and B. Then

Rate Of Reaction

Rate Of Reaction

Thus the rate of reaction at time 10 minutes

Rate Of Reaction

Units of the rate of reaction

Since concentration is usually expressed in moles / time and time is taken in seconds or minutes, the unit of the rate of reaction is moles Rate Of Reactionor Rate Of Reaction or moles Rate Of Reaction

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