Solution of Chapter 4. Chemical Kinetics (Chemistry - Exemplar Book)

The role of a catalyst is to change ___________.

In the presence of a catalyst, the heat evolved or absorbed during the reaction __________.

Activation energy of a chemical reaction can be determined by _____________.

Consider Fig. 4.1 and mark the correct option.

Consider a first order gas phase decomposition reaction given below :

A(g) → B(g) + C(g)

The initial pressure of the system before decomposition of A was p_i. After lapse of time ‘t’, total pressure of the system increased by x units and became ‘p_t’ The rate constant k for the reaction is given as _________.

According to Arrhenius equation rate constant k is equal to Ae^-Ea/RT. Which of the following options represents the graph of ln?

Consider the Arrhenius equation given below and mark the correct option.

k = A e^{–Ea /RT}

A graph of volume of hydrogen released vs time for the reaction between zinc and dil. HCl is given in Fig. 4.2. On the basis of this mark the correct option.

Which of the following statements is not correct about order of a reaction.

Consider the graph given in Fig. 4.2. Which of the following options does not show an instantaneous rate of reaction at 40th second?

Which of the following statements is correct?

Which of the following expressions is correct for the rate of reaction given below?

Which of the following graphs represents exothermic reaction?

(a)

(b)

(c)

Rate law for the reaction A + 2B → C is found to be

Rate = k [A][B]

Concentration of reactant ‘B’ is doubled, keeping the concentration of ‘A’ constant, the value of rate constant will be______.

Which of the following statements is incorrect about the collison theory of chemical reaction?

A first order reaction is 50% completed in 1.26 × 10¹⁴ s. How much time would it take for 100% completion?

Compounds ‘A’ and ‘B’ react according to the following chemical equation.

A (g) + 2 B (g) → 2C (g)

Concentration of either ‘A’ or ‘B’ were changed keeping the concentrations of one of the reactants constant and rates were measured as a function of initial concentration. Following results were obtained. Choose the correct option for the rate equations for this reaction.

Which of the following statement is not correct for the catalyst?

The value of rate constant of a pseudo first order reaction ____________.

Consider the reaction A B. The concentration of both the reactants and the products varies exponentially with time. Which of the following figures correctly describes the change in concentration of reactants and products with time?

Note : In the following questions two or more options may be correct.

Rate law cannot be determined from balanced chemical equation if _______.

Which of the following statements are applicable to a balanced chemical equation of an elementary reaction?

In any unimolecular reaction ______________.

For a complex reaction ______________.

At high pressure the following reaction is zero order.

Which of the following options are correct for this reaction?

During decomposition of an activated complex

According to Maxwell Boltzmann distributon of energy, __________.

In the graph showing Maxwell Boltzman distribution of energy, ___________.

Which of the following statements are in accordance with the Arrhenius equation?

Mark the incorrect statements.

Which of the following graphs is correct for a zero order reaction?

Which of the following graphs is correct for a first order reaction?

State a condition under which a bimolecular reaction is kinetically first order reaction.

Write the rate equation for the reaction 2A + B � � C if the order of the reaction is zero.

How can you determine the rate law of the following reaction?

2NO (g) + O₂ (g) → 2NO₂ (g)

For which type of reactions, order and molecularity have the same value?

In a reaction if the concentration of reactant A is tripled, the rate of reaction becomes twenty seven times. What is the order of the reaction?

Derive an expression to calculate time required for completion of zero order reaction.

For a reaction A + B → Products, the rate law is — Rate = k [A][B]^3/2 Can the reaction be a elementary reaction? Explain.

For a certain reaction large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?

For a zero order reaction will the molecularity be equal to zero? Explain.

For a general reaction A → B, plot of concentration of A vs time is given in Fig. 4.3. Answer the following question on the basis of this graph.

(i) What is the order of the reaction?

(ii) What is the slope of the curve?

(iii) What are the units of rate constant?

The reaction between H₂(g) and O₂(g) is highly feasible yet allowing the gases to stand at room temperature in the same vessel does not lead to the formation of water. Explain.

Why does the rate of a reaction increase with rise in temperature?

Oxygen is available in plenty in air yet fuels do not burn by themselves at room temperature. Explain.

Why is the probability of reaction with molecularity higher than three very rare?

Why does the rate of any reaction generally decreases during the course of the reaction?

Thermodynamic feasibility of the reaction alone cannot decide the rate of the reaction. Explain with the help of one example.

Why in the redox titration of KMnO₄vs oxalic acid, we heat oxalic acid solution before starting the titration?

Why can’t molecularity of any reaction be equal to zero?

Why molecularity is applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

Why can we not determine the order of a reaction by taking into consideration the balanced chemical equation?

Note: In the following questions match the items of Column I with appropriate item given in Column II.

Match the graph given in Column I with the order of reaction given in Column II. More than one item in Column I may link to the same item of Column II.

Column I Column II

(i)

(ii) (a) first order

(iii) (b) zero order

(iv)

Match the statements given in Column I and Column II

Column I Column II

(i) Catalyst alters the rate of reaction (a) cannot be fraction or zero

(ii) Molecularity (b) proper orientation is not there

Always

(iii) Second half life of first order reaction (c) by lowering the activation

Energy

(iv) e–Ea/R T (d) is same as the first

(v) Energetically favourable reactions are sometimes slow (e) total probability is one

(vi) Area under the Maxwell Boltzman curve is constant (f) refers to the fraction of molecules with energy equal

to or greater than activation

energy

Match the items of Column I and Column II.

Column I Column II

(i) Diamond (a) short interval of time

(ii) Instantaneous rate (b) ordinarily rate of conversion is

Imperceptible

(iii) Average rate (c) long duration of time

Match the items of Column I and Column II.

Column I Column II

(i) Mathematical expression for rate of reaction (a) rate constant

(ii) Rate of reaction for zero order reaction is equal to (b) rate law

(iii) Units of rate constant for zero order reaction is same as that of (c) order of slowest step

(iv) Order of a complex reaction is determined by (d) rate of a reaction

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.

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

Reason : We cannot determine order from balanced chemical equation

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

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

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