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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?

Let the reaction A → B is a 2nd order reaction w.r.t A and conc. of A is ‘a’ mol/L, then rate of reaction can be written as:

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

(i) When conc. [A] is doubled
i.e., [A’] = 2a mol/L
Then new rate of reaction

\frac{d' (x)}{dt} = k [2 a]^{2} = 4 {ka}^{2} = 4 \frac{dx}{dt}

Thus rate of reaction will become four times where concentration is doubled.

(ii) Similarly, when conc. of A is reduced to

\frac{1}{2}

i.e., [A] is a/2 then new rate of reaction,

\frac{d' (x)}{dt} = k {[\frac{a}{2}]}^{2} = \frac{1}{4} {ka}^{2} = \frac{1}{4} \frac{dx}{dt}

The rate of reaction will become one-fourth of the initial rate of reaction.

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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?

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