. Explain the following terms

(a) Explain the following terms:

(i) Rate of a reaction

(ii) Activation energy of a reaction

(b) The decomposition of phosphine, PH3 , proceeds according to the following equation


It is found that the reaction follows the following rate equation

                  Rate = k[PH3 ]

The half-life of PH3 is 37.9 s at 120°C.

(i) How much time is required for 3/4th of PH3 to decompose?

(ii) What fraction of the original sample of PH3 remains behind after 1 minute?


(a) Explain the following terms:

(i) Order of a reaction

(ii) Molecularity of a reaction

(b) The rate of a reaction increases four times when the temperature changes from 300 K to 320 K. Calculate the energy of activation of reaction, assuming that it does not change with temperature. (R = 8.314 J K–1 mol–1)

Best Answer

(a) (i) Rate of Reaction: It is defined as the decrease in the concentration of reactants per unit time or increase in the concentration of products per unit time


(ii) Activation energy: The amount of energy which the reactants must absorb to pass over the energy barrier between reactants and products is known as the activation energy

Order of a reaction

Molecularity of a reaction

(a) (i) The order of a reaction can be defined as the sum of the powers of the concentration terms as expressed in rate law.

(ii) Molecularity: It may be defined as the number of reacting species (molecules, atoms or ions) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction

 temperature changes

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