# Chemistry Class 12 NCERT Solutions: Chapter 4 Chemical-Kinetic Part 4

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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?

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.

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?

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?

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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