Notes On Effect Of Concentration On Rate, Order Of A Reaction - CBSE Class 12 Chemistry

Rate law:

The rate of a reaction decreases with a decrease in the concentration of the reactants. Thus, one of the factors that determine the rate of a reaction is the concentration of the reactants.

The representation of the rate of a reaction in terms of the concentration of its reactants is known as the rate law.

Rate ∝ [A]
Rate = k[A]

It is also called the rate equation or rate expression.

Consider the reaction:

mA +nB oC + pD

m moles of A react with n moles of B, to give o moles of C and p moles of D. We can write the rate law for this reaction is

Rate ∝ [A]x[B]y

Rate = k [A]x[B]y

This expression, which relates the rate and concentration of the reactants, is called the rate law or rate expression.

Order of the reaction:

The sum of the powers of the concentration terms in the rate law is called order of the reaction.

mA + nB → oC + pD

Rate = k [A]x[B]y

x = Order of reaction with respect to A
y = Order of reaction with respect to B

k = Rate constant
x,y = Whole number (1,2,3,...) or Fractional
x+y = Overall order of the reaction

Units of rate constant (K):

The units of K depend on the overall order of the reaction.

Rate = k [A]x[B]y

k = Rate / [A]x[B]y


The unit of k,
                           Rate of reaction / [Concentration]y+x = mol L-1 S-1 / [mol L-1]y+x

         y+x = Overall order of reaction
The Unit of  concentration in SI system is mol L-1.

y+x Unit of K
0 mol L-1 S-1
1 S-1
2 L mol-1 S-1







The Unit of k = [mol L-1 S-1]/[mol L-1]2
                   = [mol L-1 S-1]/[mol L-1]2
                   = S-1/[mol L-1]
                   = Lmol-1 S-1

Summary

Rate law:

The rate of a reaction decreases with a decrease in the concentration of the reactants. Thus, one of the factors that determine the rate of a reaction is the concentration of the reactants.

The representation of the rate of a reaction in terms of the concentration of its reactants is known as the rate law.

Rate ∝ [A]
Rate = k[A]

It is also called the rate equation or rate expression.

Consider the reaction:

mA +nB oC + pD

m moles of A react with n moles of B, to give o moles of C and p moles of D. We can write the rate law for this reaction is

Rate ∝ [A]x[B]y

Rate = k [A]x[B]y

This expression, which relates the rate and concentration of the reactants, is called the rate law or rate expression.

Order of the reaction:

The sum of the powers of the concentration terms in the rate law is called order of the reaction.

mA + nB → oC + pD

Rate = k [A]x[B]y

x = Order of reaction with respect to A
y = Order of reaction with respect to B

k = Rate constant
x,y = Whole number (1,2,3,...) or Fractional
x+y = Overall order of the reaction

Units of rate constant (K):

The units of K depend on the overall order of the reaction.

Rate = k [A]x[B]y

k = Rate / [A]x[B]y


The unit of k,
                           Rate of reaction / [Concentration]y+x = mol L-1 S-1 / [mol L-1]y+x

         y+x = Overall order of reaction
The Unit of  concentration in SI system is mol L-1.

y+x Unit of K
0 mol L-1 S-1
1 S-1
2 L mol-1 S-1







The Unit of k = [mol L-1 S-1]/[mol L-1]2
                   = [mol L-1 S-1]/[mol L-1]2
                   = S-1/[mol L-1]
                   = Lmol-1 S-1

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