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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