Chemistry 12 Chapter 4 Exemplar Solutions Chemical Kinetics Part 8

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V. Assertion and Reason Type

Note: In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(i) Both assertion and reason are correct and the reason is correct explanation of assertion.

(ii) Both assertion and reason are correct but reason does not explain assertion.

(iii) Assertion is correct but reason is incorrect.

(iv) Both assertion and reason are incorrect.

(v) Assertion is incorrect but reason is correct.

Question 57:

Assertion: Order of the reaction can be zero or fractional.

Reason: We cannot determine order from balanced chemical equation.

Answer: (ii)

Question 58:

Assertion: Order and molecularity are same.

Reason: Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of rate determining elementary step.

Answer: (v)

Question 59:

Assertion: The enthalpy of reaction remains constant in the presence of a catalyst.

Reason: A catalyst participating in the reaction, forms different activated complex and lowers down the activation energy but the difference in energy of reactant and product remains the same.

Answer: (i)

Question 60:

Assertion: All collision of reactant molecules lead to product formation..

Reason: Only those collisions in which molecules have correct orientation and sufficient kinetic energy lead to compound formation.

Answer: (v)

Question 61:

Assertion: Rate constants determined from Arrhenius equation are fairly accurate for simple as well as complex molecules.

Reason: Reactant molecules undergo chemical change irrespective of their orientation during collision.

Answer: (iii)

VI. Long Answer Type

Question 62:

All energetically effective collisions do not result in a chemical change. Explain with the help of an example.

Answer:

Hint: Proper orientation of molecule should be explained in detail.

Question 63:

What happens to most probable kinetic energy and the energy of activation with increase in temperature?

Answer:

Hint: • Flattening of curve and shifting of maxima towards high energy value. • Area under the curve beyond the activation energy increases.

Question 64:

Describe how does the enthalpy of reaction remain unchanged when a catalyst is used in the reaction.

Answer:

Hint : • Enthalpy is a state function.

• Difference in energy between reactants and product is constant.

Question 65:

Explain the difference between instantaneous rate of a reaction and average rate of a reaction.

Answer:

See NCERT textbook for Class XII.

Question 66:

With the help of an example explain what is meant by pseudo first order reaction.

Answer:

See NCERT textbook for Class XII.

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