Chemical Kinetics-NCERT Exemplar Problems & Solution

MCQs-Type-I

Question: 1. The role of catalyst is to change __________.

(i) gibbs energy of reaction.

(ii) enthalpy of reaction.

(iii) activation energy of reaction.

(iv) equilibrium constant.

Answer: (iii) activation energy of reaction.

Question: 2. In the presence of a catalyst, the heat evolved or absorbed during the reaction __________.

(i) increases.

(ii) decreases.

(iii) remains unchaged.

(iv) may increase or decrease.

Answer: (iii) remains unchaged.

Question: 3. Activation energy of a chemical reaction can be determined by ________.

(i) determining the rate of constant at standard temperature.

(ii) determining the rate of contsnts at two temperatures.

(iii) determining probability of collision.

(iv) using catalyst.

Answer: (ii) determining the rate of contsnts at two temperatures.

Question: 4. Consider the figure and mark the correct option.

(i) Activation energy of forward reaction is `E_1 + E_2` and product is less stable than reactant.

(ii) Activation energy of forward reaction is `E_1+E_2` and product is more stable than reactant.

(iii) Activation energy of both forward and backward reaction is `E_1+E_2` and reactant is more stable than product.

(iv) Activation energy of backward reaction is `E_1` and product is more stable than reactant.

Answer: (i) Activation energy of forward reaction is `E_1 + E_2` and product is less stable than reactant.

Question: 5. 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 _________.

(i) `k = (2.303)/t log p_i/(p_t-x)`

(ii) `k = (2.303)/t log p_i/(2p_i-p_t)`

(iii) `k = (2.303)/t log p_i/(2p_i+p_t)`

(iv) `k = (2.303)/t log p_i/(2p_i+x)`

Answer: (ii) `k = (2.303)/t log p_i/(2p_i-p_t)`

Question: 6. According to Arrhenius equation rate constant k is equal to `Ae^(-E_a/(RT)`.

Which of the following options represents the graph of ln `k` vs `1/T`

(i)

(ii)

(iii)

(iv)

Answer: (i)

Question: 7. Consider the Arrhenius equation given below and mark the correct option. `k = Ae^(-E_a/(RT)`

(i) Rate constant increases exponentially with increasing activation energy and decreasing temperature.

(ii) Rate constant decreases exponentially with increasing activation energy and decreasing temperature.

(iii) Rate constant increases exponentially with decreasing activation energy and decreasing temperature.

(iv) Rate constant increases exponentially with decreasing activation energy and increasing temperature.

Answer: (iv) Rate constant increases exponentially with decreasing activation energy and increasing temperature.

Question: 8. A graph of volume of hydrogen released vs time for the reaction between zinc and dil. HCl is given in Figure. On the basis of this mark the correct option.

(i) Average rate upto 40s is `(V_3-V_2)/40`

(ii) Average rate upto 40 seconds is `(V_3-V_2)/(40-30)`

(iii) Average rate upto 40 seconds is `V_3/40`

(iv) Average rate upto 40 seconds is `(V_3-V_1)/(40-20)`

Answer: (iii) Average rate upto 40 seconds is `V_3/40`

Question: 9. Which of the following statements is not correct about order of a reaction.

(i) The order of a reaction can be a fractional number.

(ii) Order of a reaction is experimentally determined quantity.

(iii) The order of a reaction is always equal to the sum of the stoichiometric coefficients of reactants in the balanced chemical equation for a reaction.

(iv) The order of a reaction is the sum of the powers of molar concentration of the reactants in the rate law expression.

Answer: (iii) The order of a reaction is always equal to the sum of the stoichiometric coefficients of reactants in the balanced chemical equation for a reaction.

Question: 10. Consider the graph given in Figure. Which of the following options does not show instantaneous rate of reaction at 40^th second?

(i) `(V_5-V_2)/(50-30)`

(ii) `(V_4-V_2)/(50-30)`

(iii) `(V_3-V_2)/(40-30)`

(iv) `(V_3-V_1)/(40-20)`

Answer: (ii) `(V_4-V_2)/(50-30)`

Question: 11. Which of the following statements is correct?

(i) The rate of a reaction decreases with passage of time as the concentration of reactants dereases.

(ii) The rate of a reaction is same at any time during the reaction.

(iii) The rate of a reaction is independent of temperature change.

(iv) The rate of a reaction decreases with increase in concentration of reactant(s).

Answer: (i) The rate of a reaction decreases with passage of time as the concentration of reactants dereases.

Question: 12. Which of the following expressions is correct for the rate of reaction given below?

`5Br^- (aq) + BrO_3^-(aq) + 6H^+(aq) ->3Br_2(aq) + 3H_2O(l)`

(i) `(Delta[Br^-])/(Delta t) = 5(Delta[H^+])/(Delta t)`

(ii) `(Delta[Br^-])/(Delta t) = 6/5\(Delta[H^+])/(Delta t)`

(iii) `(Delta[Br^-])/(Delta t) = 5/6\(Delta[H^+])/(Delta t)`

(iv) `(Delta[Br^-])/(Delta t) = 6(Delta[H^+])/(Delta t)`

Answer: (iii) `(Delta[Br^-])/(Delta t) = 5/6\(Delta[H^+])/(Delta t)`

Question: 13. Which of the following graphs represents exothermic reaction?

(a)

(b)

(c)

(i) (a) only

(ii) (b) only

(iii) (c) only

(iv) (a) and (b)

Answer: (i) (a) only

Question: 14. 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______.

(i) the same

(ii) doubled

(iii) quadrupled

(iv) halved

Answer: (ii) doubled

Question: 15. Which of the following statements is incorrect about the collison theory of chemical reaction?

(i) It considers reacting molecules or atoms to be hard spheres and ignores their structural features.

(ii) Number of effective collisions determines the rate of reaction.

(iii) Collision of atoms or molecules possessing sufficient threshold energy results into the product formation.

(iv) Molecules should collide with sufficient threshold energy and proper orientation for the collision to be effective.

Answer: (iii) Collision of atoms or molecules possessing sufficient threshold energy results into the product formation.

Question: 16. A first order reaction is 50% completed in `1.26 xx 10^14\ s`. How much time would it take for 100% completion?

(i) `1.26 xx 10^15 s`

(ii) `2.52 xx 10^14 s`

(iii) `2.52 xx 10^28 s`

(iv) infinite

Answer: (iv) infinite

Question: 17. 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.

(i) Rate = `k [A]^2[B]`

(ii) Rate = `k [A] [B]^2`

(iii) Rate = `k [A] [B]`

(iv) Rate = `k [A]^2 [B]^0`

Answer: (ii) Rate = `k [A] [B]^2`

Question: 18. Which of the following statement is not correct for the catalyst?

(i) It catalyses the forward and backward reaction to the same extent.

(ii) It alters `DeltaG` of the reaction.

(iii) It is a substance that does not change the equilibrium constant of a reaction.

(iv) It provides an alternate mechanism by reducing activation energy between reactants and products.

Answer: (ii) It alters `DeltaG` of the reaction.

Question: 19. The value of rate constant of a pseudo first order reaction _________.

(i) depends on the concentration of reactants present in small amount.

(ii) depends on the concentration of reactants present in excess.

(iii) is independent of the concentration of reactants.

(iv) depends only on temperature.

Answer: (ii) depends on the concentration of reactants present in excess.

Question: 20. 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?

(i)

(ii)

(iii)

(iv)

Answer: (ii)

 

II. Multiple Choice Questions (Type-II)

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

Question: 21. Rate law cannot be determined from balanced chemical equation if _______.

(i) reverse reaction is involved.

(ii) it is an elementary reaction.

(iii) it is a sequence of elementary reactions.

(iv) any of the reactants is in excess.

Answer:

(i) reverse reaction is involved,

(iii) it is a sequence of elementary reactions.

And

(iv) any of the reactants is in excess.

Question: 22. Which of the following statements are applicable to a balanced chemical equation of an elementary reaction?

(i) Order is same as molecularity.

(ii) Order is less than the molecularity.

(iii) Order is greater than the molecularity.

(iv) Molecularity can never be zero.

Answer:

(i) Order is same as molecularity.

And

(iv) Molecularity can never be zero.

Question: 23. In any unimolecular reaction ______________.

(i) only one reacting species is involved in the rate determining step.

(ii) the order and the molecularity of slowest step are equal to one.

(iii) the molecularity of the reaction is one and order is zero.

(iv) both molecularity and order of the reaction are one.

Answer:

(i) only one reacting species is involved in the rate determining step.

And

(ii) the order and the molecularity of slowest step are equal to one.

Question: 24. For a complex reaction ______________.

(i) order of overall reaction is same as molecularity of the slowest step.

(ii) order of overall reaction is less than the molecularity of the slowest step.

(iii) order of overall reaction is greater than molecularity of the slowest step.

(iv) molecularity of the slowest step is never zero or non interger.

Answer:

(i) order of overall reaction is same as molecularity of the slowest step.

And

(iv) molecularity of the slowest step is never zero or non interger.

Question: 25. At high pressure the following reaction is zero order.

`2NH_3(g)` `N_2(g) + 3H_2`

Which of the following options are correct for this reaction?

(i) Rate of reaction = Rate constant

(ii) Rate of the reaction depends on concentration of ammonia.

(iii) Rate of decomposition of ammonia will remain constant until ammonia disappears completely.

(iv) Further increase in pressure will change the rate of reaction.

Answer:

(i) Rate of reaction = Rate constant

(iii) Rate of decomposition of ammonia will remain constant until ammonia disappears completely.

And

(iv) Further increase in pressure will change the rate of reaction.

Question: 26. During decomposition of an activated complex

(i) energy is always released

(ii) energy is always absorbed

(iii) energy does not change

(iv) reactants may be formed

Answer:

(i) energy is always released

And

(iv) reactants may be formed

Question: 27. According to Maxwell Boltzmann distribution of energy, __________.

(i) the fraction of molecules with most probable kinetic energy decreases at higher temperatures.

(ii) the fraction of molecules with most probable kinetic energy increases at higher temperatures.

(iii) most probable kinetic energy increases at higher temperatures.

(iv) most probable kinetic energy decreases at higher temperatures.

Answer:

(i) the fraction of molecules with most probable kinetic energy decreases at higher temperatures.

 

And

(iii) most probable kinetic energy increases at higher temperatures.

Question: 28. In the graph showing Maxwell Boltzman distribution of energy, ___________.

(i) area under the curve must not change with increase in temperature.

(ii) area under the curve increases with increase in temperature.

(iii) area under the curve decreases with increase in temperature.

(iv) with increase in temperature curve broadens and shifts to the right hand side.

Answer:

(i) area under the curve must not change with increase in temperature.

And

(iv) with increase in temperature curve broadens and shifts to the right hand side.

Question: 29. Which of the following statements are in accordance with the Arrhenius equation?

(i) Rate of a reaction increases with increase in temperature.

(ii) Rate of a reaction increases with decrease in activation energy.

(iii) Rate constant decreases exponentially with increase in temperature.

(iv) Rate of reaction decreases with decrease in activation energy.

Answer:

(i) Rate of a reaction increases with increase in temperature.

And

(ii) Rate of a reaction increases with decrease in activation energy.

Question: 30. Mark the incorrect statements.

(i) Catalyst provides an alternative pathway to reaction mechanism.

(ii) Catalyst raises the activation energy.

(iii) Catalyst lowers the activation energy.

(iv) Catalyst alters enthalpy change of the reaction.

Answer:

(ii) Catalyst raises the activation energy.

And

(iv) Catalyst alters enthalpy change of the reaction.

Question: 31. Which of the following graphs is correct for a zero order reaction?

(i)

(ii)

(iii)

(iv)

Answer:

(i)

And

(iv)

Question: 32. Which of the following graphs is correct for a first order reaction?

(i)

(ii)

(iii)

(iv)

Answer:

(i)

And

(iv)

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