• Molecularity :
• The number of atoms, ions or molecules of the reactant that take part in the reaction and which experience collision with each other so that the reaction results, it is called molecularity
• Hence, the orders of reactions and molecularities of bimolecular, trimolecular and elementary reaction are same.
• The possibility of collision of three or more molecules with one another and to result in the reaction is less.
• The molecularity more than three is not seen.
• Pseudo – unimolecular or Pseudo first order reaction :
• Those reaction which are not truly of the first order but under certain conditions become reactions of the first order. Examples :
(i) Hydrolysis of ethyl acetate.
(ii) Hydrolysis of cane sugar.
• Determination of order of reaction :
Methods : (i) Intial rate method
(ii) Integrated rate equation method or Graphical method
(iii) Half life method
(iv) Ostwald’s isolation method
• Ostwald’s Isolation method :
• In certain reaction there is involvement of more than one reactants. In this method, the concentration of other reactants in comparison to one reactant is taken in very large proportion.
The reaction rate will be indicative with respect to reactant with less concentration because the concentration of other reactants remain almost constant.
• Half life method :
• The time taken for half of the reaction to complete.
• It is very simple method.
• Effect of catalyst :
• The main function of catalyst is decrease the activation energy, bring energy barrier down and increases the rate of reaction.
• Equilibrium constant (K) is not changed.
• Rate of reaction increases.
55. The minimum amount of energy required for the reacting molecules to undergo reaction is called :
(a) potential energy (b) internal energy (c) activation energy (d) threshold energy
56. Increase in the concentration of the reactants leads to the change in
(a) heat of reaction (b) threshold energy (c) collision energy (d) activation energy
57. Energy of activation of an exothermic reaction is
(a) zero (b) negative
(c) positive (d) can not be predicated
58. The chemical reactions in which reactants require high amount of activation energy are generally _____
(a) slow (b) fast (c) instantaneous (d) spontaneous
59. The rate of reaction increases with increase of temperature because ____
(a) an increase in the number of activated molecules
(b) an increase in the number of collisions
(c) lowering of threshold energy
(d) activation energy is lowered
60. The activation energy of reaction is equal to
(a) Threshold energy + Energy of the products
(b) Threshold energy - Energy of the reactants
(c) Threshold energy + Energy of the reactants
(d) Threshold energy - Energy of the products
61. Collision theory is most satisfactory for ___________ reaction.
(a) First order (b) second order (c) Bimolecular (d) Any
