Chemistry Class 12 NCERT Solutions: Chapter 4 Chemical-Kinetic Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Chemical Kinetics Rate of Reaction

Q: 4. The decomposition of dimethyl ether leads to the formation of and the reaction rate is given by

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.. ,

If the pressure is, measured in bar and time in minutes, then what are the units of rate and rate constants?

Answer:

If pressure is measured in bar and time in minutes, then

Unit of

Therefore, unit of rate constants

Q: 5. Mention the factors that affect the rate of a chemical reaction.

Answer:

The factors that affect the rate of a reaction areas follows.

(i) Concentration of reactants (pressure in case of gases)

(ii) Temperature

(iii) Presence of a catalyst

(iv) Nature of reactant

Q: 6. A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is

(i) doubled (ii) reduced to half?

Answer:

Let the concentration of the reactant be

Rate of reaction,

(i) If the concentration of the reactant is doubled, , then the rate of the reaction would be

Therefore, the rate of the reaction would increase by times.

(ii) If the concentration of the reactant is reduced to half, i.e.. , then the rate of the reaction would be

Therefore, the rate of the reaction would be reduced to

Q: 7. What is the effect of temperature on the rate constant of a reaction? How can this temperature effect on rate constant be represented quantitatively?

Answer:

The rate constant is nearly doubled with a rise in temperature by 10° for a chemical reaction.

The temperature effect on the rate constant can be represented quantitatively by Arrhenius equation,

where, the rate constant,

A is the Arrhenius factor or the frequency factor,

R is the gas constant,

T is the temperature, and

is the energy of activation for the reaction

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