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Chemical Kinetics

Short Answer Type

211. The rate of reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction that it does not change with temperature.

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

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Long Answer Type

213. What is the effect of temperature on the rate constant of reaction? How can this effect of temperature on rate constant be respresented quantitatively?

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214.

For a certain chemical reaction variation in the concentration in [R] vs time(s) plot is given below:
For the reaction write/draw
(i) What is the order of the reaction?
(ii) What are the units of rate constant K?

(iii) Give the relationship between K and t_1/2 (half-life period).
(iv) What does the slope of the above line indicate?
(v) Draw the plot Vs. time(s).
Or
For a certain chemical reaction:
$A + 2 B ⇋ 2 C + D$
The experimentally obtained information is tabulated below:

The experimentally obtained information is tabulated below :

Exp.

[A]₀

[B]₀

Initial rate of reaction

0.30

0.60

0.30

0.60

0.30

0.60

0.096

0.384

0.192

0.768

For this reaction:
(i) Derive the order of reaction w.r.t. both the reactants A and B.
(ii) Write the rate law.
(iii) Calculate the value of rate constant K.
(iv) Write the expression for the rate of reaction in terms of A and C.

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215. What do you mean by zero order reaction? How the value of rate constant is determined? What is the relation between rate constant and half-life period?

When the rate of the reaction is independent of the concentration of the reactants, the reaction is known as zero order reaction. In zero order reaction, the concentration of reactant (R) remains unaltered during the course of reaction.
It means

rate equals fraction numerator negative straight d open square brackets straight R close square brackets over denominator dt end fraction equals straight k open square brackets straight R close square brackets degree space equals space straight k

straight d open parentheses straight R close parentheses space equals space minus straight k space dt

on integration of this equation, we get

open square brackets straight R close square brackets space equals space minus kt plus constant

...(i)
Since

open square brackets straight R close square brackets space equals space open square brackets straight R close square brackets degree

where t = 0 (i.e., no product is formed at the beginning of the reaction), the constant must be zero.
Thus, [R]° = – K x 0 = constant
Constant = [R]°
Put the value of constant in eqn. (i), we get
[R] = – kt + [ R]° ...(ii)
When a plot is drawn between concentration of reactant (R) and time t, a straight line is obtained, slope of which gives the value of – k and intercept on y-axis is equal to the value of [R]°.
Alternatively, the value of k can be obtained from eqn. (i) by putting the value of concentration, [R] at any time t and initial concentration, [R]°. When the rate of the reaction is independent of the concentration of

When the rate of the reaction is independent of the concentration of

Hence,

straight k equals fraction numerator open square brackets straight R close square brackets degree minus open square brackets straight R close square brackets straight t over denominator straight t end fraction

Half life period is the time period to reduce the initial concentration of the reactant to half of its initial value.
Thus,

straight t subscript 1 divided by 2 end subscript space equals space fraction numerator open square brackets straight R close square brackets minus begin display style 1 half end style open square brackets straight R close square brackets degree over denominator straight k end fraction space equals fraction numerator open square brackets straight R close square brackets degree over denominator 2 straight k end fraction

Thus, the half life period is directly proportional to the initial concentration of the reactant, [R]° and inversely proportional to the rate constant k.

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216. For the reaction A → B, deduce the integrated form of rate law. What will be the nature of the curve when concentration is plotted against time for such reaction?

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217.

Answer the following questions on the above curve for a first order reaction A → P.
(a) What is the relation between slope of this line and rate constant.
(b) (i) Calculate the rate constant of the above reaction if the slope is 2 x 10^–4 s^–1.
(ii) Derive the relationship between half life of a first order and its rate constant.

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