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Chemical Kinetics

Short Answer Type

81. Which of the reactions slow or fast, will have higher activation energy?

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82. What information can we had from the statement that the energy of activation of a reaction is zero?

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83. Define collision frequency factor.

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84. For the reaction H₂ + I₂ → 2HI, What is the molecularity of the reaction?

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85. Define the term ‘order of reaction’ for chemical reactions.

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86. The decomposition of dimethyl ether leads to the formation of CH₄, H₂ and CO and the rate is given by
Rate = k[CH₃OCH₃]^3/2
The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, i.e.,
Rate = k pCH₃O CH₃^3/2.
If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?

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87. List the factors on which the rate of a chemical reaction depends.

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Long Answer Type

88. From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants
(i) 3NO(g) → N₂O (g) Rate = k[NO]²
(ii) H₂O₂ (aq) + 3I^– (aq) + 2H⁺ → 2H₂O (l) + I^-₃Rate = k[H₂O₂][I^-]
(iii) CH₃CHO (g) → CH₄ (g) + CO(g) Rate = k [CH₃CHO]3/2
(iv) C₂H₅Cl (g) → C₂H₄ (g) + HCl (g) Rate = k [C₂H₅Cl]

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89. A reaction is second order with respect to a reactant. How is the rate of rection affected if the concentration of the reactant is
(i) Doubled
(ii) Reduced to 1/2?

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90. A reaction is first order in A and second order in B
(i) Write differential rate equation.
(ii) How is the rate affected when the concentration of B three times?
(iii) How is the rate affected when the concentrations of both A and B are doubled?

(i) Differential rate equation of reaction is

\frac{dx}{dt} = k [A]^{1} [B]^{2} = k [A] [B]^{2}

(ii) When conc. of B is tripled, it means conc. of B becomes [3 x B]
∴ New rate of reaction,

\frac{dx'}{dt} = k [A] [3 B]^{2} = 9 k [A] [B]^{2} = 9 (\frac{dx}{dt})

i.e., rate of reaction will become 9 times.

(iii) When conc. of A is doubled and that of B is also doubled, then conc. of A becomes [2A] and that of B becomes [2B] rate of reaction