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141. What is meant by the ‘rate constant’ K of a reaction? If the concentration be expressed in mol L^–1 units and time in seconds, what would be the units for K

(i) for a zero order reaction
(ii) for a first order reaction?

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Long Answer Type

142. For the reaction
: 2A + B + C → A₂B
the rate = k[A] [B]² with k = 2.0 x 10^–6 mol^–2L²s^–1.
Calculate the initial rate of the reaction when [A] = 0.1 mol L^-1, [B] = 0.2 mol L^-1and [C] = 0.8 M. Calculate the rate of reaction after [A] is reduced to 0.06 mol L^–1.

263 Views

Short Answer Type

143. The decomposition of NH₃ on platinum surface is zero order. What are the rates of production of N₂ and H₂ if k = 2.5 x 10^–4 mol^–1Ls^–1?

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144. In a pseudo first order hydrolysis of ester in water the following results were obtained:

t / s

0

30

60

90

Ester / mol L^–1

0.55

0.31

0.17

0.085

(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(ii) Calculate the pseudo first order rate constant for the hydrolysis of ester.

(i) Average rate of reaction between interval of time 30 to 60 second is given by

Average space rate space equals space fraction numerator increment straight x over denominator increment straight t end fraction equals fraction numerator straight C subscript 2 minus straight C subscript 1 over denominator increment straight t end fraction space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 0.17 minus 0.3 over denominator 60 minus 30 end fraction space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 0.14 over denominator 30 end fraction space equals space minus 0.00467 space space space space space space space space space space space space space space space space space space space space space space space equals space minus 4.67 space cross times space 10 to the power of negative 3 end exponent space Ms to the power of negative 1 end exponent

Minus sign shows that rate of reaction is decreasing with time as conc. of ester is decreasing with time.
(ii) Pseudo first order rate constant k is given by

straight k equals fraction numerator 2.303 over denominator straight t end fraction log fraction numerator straight a over denominator straight a minus straight x end fraction

where a is initial conc. and (a – x) conc. after time t. Here a = 0.55 M.
(i) Average rate of reaction between interval of time 30 to 60 second

The nearly equal values of k confirms that reaction is of first order.
The actual value of rate constant is the average of three values of k.
Therefore, rate constant of reaction

straight k equals fraction numerator straight k subscript 1 plus straight k subscript 2 plus straight k subscript 3 over denominator 3 end fraction space space space equals fraction numerator left parenthesis 1.91 plus 1.96 plus 2.06 right parenthesis cross times 10 to the power of negative 2 end exponent over denominator 3 end fraction space space space equals space 1.97 space cross times space 10 to the power of negative 2 end exponent space straight s to the power of negative 1 end exponent.

336 Views

Long Answer Type

145. In a reaction between A and B, the initial rate of reaction (r₀) was measured for different initial concentrations of A and B as given below:

A/mol L^–1	0.20	0.20	0.40
B/mol L^–1	0.30	0.10	0.05
r/mol L^–1S^–1	5.07 x 10^–5	5.07 x 10^–5	1.43 x 10^–4

What is the order of the reaction with respect of A and B?

142 Views

146. The following results have been obtained during the kinetic studies of the reaction:

2A + B → C + D

exp.	[A]/ mol L^–1	[B]/M	Initial rate of formation of D/mol L^–1 min^–1
I	0.1	0.1	6.0 x 10^–3
II	0.3	0.2	7.2 x 10^–2
III	0.3	0.4	2.88 x 10^–1
IV	0.4	0.1	2.40 x 10^–2

Determine the rate law and the rate constant for the reaction.

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147. e reaction between A and B is first order with respect to A and zero order with respect to B. Fill in the blanks in the following table:

exp.	[A]/ mol L^–1	[B]/M	Initial rate of formation of D/mol L^–1 min^–1
I	0.1	0.1	2.0 x 10^–2
II	-	0.2	4.0 x 10^–2
III	0.4	0.4	-
IV	-	0.2	2.0 x 10^–2

163 Views

148. Calculate the half life of a first order reaction from their rate constants given below:
(i) 200 s^–1 (ii) 2 min^–1 (iii) 4 years^–1

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149. The experimental data for decomposition of N₂O₅ [2N₂O_s → 4NO₂ + O₂] in gas phase at 318 k are given below:

(a) Plot [N₂O₅] again t.
(b) Find the half life period for the reaction.
(c) Draw a graph between log [N₂O₅] and t.
(d) What is rate law?
(e) Calculate the rate constant.
(f) Calculate the half life period from K and compare it with (ii).

428 Views

Short Answer Type

150. The rate constant for a first order reaction is 60 S^–1. How much time will it take to reduce the initial concentration of the reactant to its 1/16th value ?

375 Views