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Chemical Kinetics

Short Answer Type

111. The gas phase decomposition of acetaldehyde.

{CH}_{3} CHO (g) \to {CH}_{4} (g) + CO (g)

at 680 K is observed to follow the rate expression.

Rate \frac{- d [{CH}_{3} CHO]}{dt} = k {[{CH}_{3} CHO]}^{3 / 2}

If the rate of decomposition is followed by monitoring the partial pressure of the acetaldehyde we can express the rate as

\frac{- {dP}_{{CH}_{3} CHO}}{dt} = k {[P_{{CH}_{3} CHO}]}^{3 / 2}

If the pressure is measured in atmosphere and time in minutes, then
(a) What are the units of the rate of reaction?
(b) What are the units of rate constant k?

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112.

(a) Show graphically how the rate of first order reaction vary with only one reactant depends concentration of reactant.
(b) Give one example of first order reaction.

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113. Suggest explainations for:
The increased speed of a simple bimolecular change when temperature of the reaction mixture is increased.

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114. Suggest explainations for:
The action of a solid phase catalyst to increase the rate of unimolecular gas—phase decomposition reaction.

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115. Suggest explainations for:
One gram of pulverized wood burns faster than one gram piece of wood.

The rate of reaction depend upon the surface are a of reacting species. Pulverized wood has greater surface area as compared to one gram of piece of wood so it comes in contact with oxygen to much more extent and get burnt much faster.

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Long Answer Type

116.

(i) Define specific reaction rate.
(ii) Define Half-life period of a chemical reaction. Also obtain the expression for half-life period.

Or

Derive the general for of the expression for the half-life of a first order reaction.

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Short Answer Type

117. How can the rate of a fast reaction be determined by Flash Photolysis?

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118. How does temperature affect the rate of a reaction? Is there a corresponding equal decrease in number of collisions among molecules of a gaseous reaction? How is this effect explained by the concept of activation energy?

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119. Nitric oxide reacts with hydrogen to give nitrogen and water:

2 NO + 2 H_{2} \to N_{2} + 2 H_{2} O

The kinetic of this reaction is explained by the following steps:

(i) 2NO + H₂ → N₂ + H₂O₂ (slow)
(ii) H₂O₂+ H₂ → 2H₂O (fast)
What is the predicted law?

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