CBSE Questions for Class 12 Engineering Chemistry Chemical Kinetics Quiz 3 - MCQExams.com

If the rate with respect to $$O_2, NO, NO_2$$ are $$\displaystyle \frac{- \Delta [O_2]}{\Delta t}$$ $$= \dfrac{-1}{2}\dfrac{\Delta [NO]}{\Delta t} = \dfrac{+1}{2} \dfrac{\Delta [NO_2]}{\Delta t}$$, then the corresponding chemical equation is $$2NO+O_2  \rightarrow NO_2$$.
  • True
  • False
An increase in the rate of a reaction for a rise in temperature is due to:
  • increase in collision frequency
  • shortening of mean free path
  • increase in the number of activated molecules
  • none of the above
For a first order reaction $$A\rightarrow B$$ the rate constant is $$x\ min^{−1}$$ . If the initial concentration of A is 0.01M , the concentration of A after one hour is given by the expression:
  • $$0.01e^{-x}$$
  • $$1\times10^{-2}(1-e^{-60x})$$
  • $$(1\times10^{-2}) e^{-60x}$$
  • None of these
Which statements are correct in terms of chemical kinetic stuides?
  • The quenching of a reaction can be made by cooling the reaction mixture.
  • The quenching of a reaction can be made by diluting the reaction mixture.
  • The reaction is supposed to be completed if it is kept for long time or strongly heated.
  • None of the above
All first order reactions are unimolecular.
  • True
  • False

To initiate a reaction, minimum energy which is required to break bonds is called

  1. bond energy
  2. activation energy
  3. breaking energy
  4. ionization energy
  • 1
  • 2
  • 3
  • 4
Radioactive disintegration follows _____ order kinetic.
  • zero
  • pseudo first
  • first
  • second
Time required to complete half of the reactant in a zero order reaction is equal to a/(2k).
  • True
  • False
If 'a' is the initial concentration of a substance which reacts according to zero order kinetics and K is rate constant, the time for the reaction to go to completion is:
  • a/K
  • 2/Ka
  • K/a
  • 2K/a
Activation energy of a reaction is:
  • the energy released during the reaction.
  • the energy evolved when activated complex is formed.
  • additional amount of energy needed by the reactants to overcome the potential barrier of reaction.
  • the energy needed to form one mole of the product.
Calculate the partial pressure of reactants and products, when azomethane decomposed at an initial pressure of 200 mm for 30 minutes according to
$$(CH_3)_2N_2\rightarrow C_2H_6+N_2$$
The rate constant is $$2.5\times 10^{-4} sec^{-1}$$.
  • $$P'(CH_3)_2N_2=12.755 mm, P'C_2H_6=72.45 mm, P'N_2=724.5 mm$$
  • $$P'(CH_3)_2N_2=127.55 mm, P'C_2H_6=72.45 mm, P'N_2=72.45 mm$$
  • $$P'(CH_3)_2N_2=1275.5 mm, P'C_2H_6=72.45 mm, P'N_2=724.5 mm$$
  • None of these
At room temperature, the reaction between $$NO$$ and $$O_2$$ to give $$NO_2$$ is fast, while that between $$CO$$ and $$O_2$$ is slow. It is due to:
  • CO is smaller in size than that of NO
  • CO is poisonous
  • the activation energy for the reaction, $$2NO+O_2\rightarrow 2NO_2$$ is less than $$2CO+O_2\rightarrow 2CO_2$$
  • none of the above
A first order reaction has a half-life period of 69.3 sec. At $$0.10\ M$$ reactant concentration, rate will be:
  • $$10^{-3}\ M. sec^{-1}$$
  • $$10^{-4}\ M. sec^{-1}$$
  • $$10^{-2}\ M .sec^{-1}$$
  • None of these
For a reaction for which the activation energies of forward and reverse reactions are equal:
  • $$\Delta H=0$$
  • $$\Delta S=0$$
  • the order is zero
  • there is no catalyst
The rate constant for an isomerisation reaction, $$A\rightarrow B$$ is $$4.5\times 10^{-3} min ^{-1}$$. If the initial concentration of A is 1 M,  the rate of the reaction after 1 hr will be: 
  • $$3.4354\times 10^{-3}$$
  • $$4.4554\times 10^{-3}$$
  • $$5.4364\times 10^{-3}$$
  • None of these
The activation energy for a chemical reaction depends upon:
  • reaction
  • nature of reacting species
  • frequency factor
  • concentration of reacting species
$$A\rightarrow B+2C$$

At $$100^oC$$, in above gaseous reaction, is observed to be of the first order. On starting with pure A, at the end of $$14$$ minutes, the total pressure found to be $$264$$ mm of Hg. After a long time, the total pressure of the system was $$450$$ mm of Hg. 
Rate constant of the reaction is:
  • $$6.455\times 10^{-2} min^{-1}$$
  • $$3.415\times 10^{-2} min^{-1}$$
  • $$5.575\times 10^{-2} min^{-1}$$
  • none of these
For a first-order reaction, $$A\rightarrow Product$$, the initial concentration of A is 0.1M and after 40 minutes it becomes 0.025 M. Calculate the rate of reaction at reactant concentration of 0.01 M:
  • $$3.47\times 10^{-4} M .min^{-1}$$
  • $$3.47\times 10^{-5} M. min^{-1}$$
  • $$1.735\times 10^{-6} M. min^{-1}$$
  • $$1.735\times 10^{-4} M. min^{-1}$$
The maximum value of activation energy is equal to:
  • zero
  • heat of reaction
  • threshold energy
  • none of these
In a first order reaction the concentration of reactant decreases from 800 $$mol/dm^3$$ to $$50\ mol/dm^3$$ in $$2\times 10^4 sec$$. The rate constant of reaction in $$sec^{-1}$$ is:
  • $$2.000\times 10^{4}$$
  • $$3.415\times 10^{-5}$$
  • $$1.386\times 10^{-4}$$
  • $$2.000\times 10^{-4}$$
Which of the following is not correct reason for the substantially lower rate of reaction than the collision frequency?
  • All the collisions do not attain threshold energy level
  • The activated complex formed is short lived
  • All the collisions do not have proper orientation
  • Effective collision are lesser in number than all collisions
Effective collisions are those in which molecules must:
  • have energy equal to or greater than the threshold energy
  • have proper orientation
  • acquire the energy of activation
  • all of the above
The rate constant of a reaction is 0.0693 $$min^{-1}$$. Starting with 10 mol, the rate of the reaction after 10 min is:
  • 0.0693 mol $$min^{-1}$$
  • 0.0693 $$\times$$ 2 mol $$min^{-1}$$
  • 0.0693 $$\times$$ 5 mol $$min^{-1}$$
  • 0.0693 $$\times\, 5^2$$ mol $$min^{-1}$$
The activation energy for a simple chemical reaction $$A\, \rightarrow\, B\, is\, E_a$$ in the forward reaction. The activation energy of the reverse reaction:
  • Is negative of $$E_a$$
  • Is always less than $$E_a$$
  • Can be less than or more than $$E_a$$
  • Is always double of $$E_a$$
The decomposition of $$Cl_2O_7$$ at $$400$$ K in the gas phase to $$Cl_2$$ and $$O_2$$ is of $$1^{st}$$ order. After $$55$$ sec at 400 K, the pressure of $$Cl_2O_7$$ falls from $$0.062$$ to $$0.044$$ atm. 

The rate constant is :
  • $$6.24\times 10^{-3} sec^{-1}$$
  • $$5.20\times 10^{-3} sec^{-1}$$
  • $$7.34\times 10^{-3} sec^{-1}$$
  • none of the above
For a first-order reaction, the ratio of times to complete 99.9% and half of the reaction is:
  • $$8$$
  • $$9$$
  • $$10$$
  • $$12$$
The activation energy for a simple chemical reaction, $$A\rightarrow{B}$$ is $$E_a$$ in forward direction. The activation energy for the reverse reaction:
  • is negative of $$E_a$$
  • is always less than $$E_a$$
  • can be less than or more than $$E_a$$
  • is always double of $$E_a$$
80% of a first order reaction was completed in 70 min. How much it will take for 90% completion of a reaction ?
  • 114 min
  • 140 min
  • 100 min
  • 200 min
For a given reaction of the first order, it takes 15 minutes for the concentration to drop from 0.8 M to 0.4 M. The time required for the concentration to drop from 0.1 M to 0.025 M will be:
  • 60 minutes
  • 15 minutes
  • 7.5 minutes
  • 30 minutes
The mathematical expression for $$t_{1/4}$$ i.e., when $$(1/4)^{th}$$ reaction is over following first-order kinetics can be given by:
  • $$t_{1/4}=\frac {2.303}{K}log 4$$
  • $$t_{1/4}=\frac {2.303}{K}log 2$$
  • $$t_{1/4}=\frac {2.303}{K}log \frac {4}{3}$$
  • $$t_{1/4}=\frac {2.303}{K}log \frac {3}{4}$$
The rate of a chemical reaction generally increases rapidly even for small temperature increase because of a rapid increase in:
  • Collision frequency
  • Fraction of molecules with energies in excess of the activation energy
  • Activation energy
  • Average kinetic energy of molecules
In a reaction, 5 g ethyl acetate is hydrolyzed per litre in the presence of dil. HCl in 300 min.If the reaction is of the first order and the initial concentration of ethyl acetate is  22 g $$L^{-1}$$, the rate constant of the reaction is:
  • $$k \,=\, 8.6\,\times\, 10^{-4}\, min^{-1}$$
  • $$k \,=\, 1.4\,\times\, 10^{-4}\, min^{-1}$$
  • $$k \,=\, 6.9\,\times\, 10^{-4}\, min^{-1}$$
  • $$None \:of \:these $$

What specific name can be given to the following sequence of steps: $$Hg + hv \rightarrow\, Hg^*$$

$$Hg^*\, +\, H_2\, \rightarrow\, H_2^*\, +\, Hg$$
  • Fluorescence
  • Phosphorescence
  • Photosensitization
  • Chemilumionescence
In a multistep reaction such as $$A + B$$ $$\rightarrow\, Q\, \rightarrow\, C.$$ The potential energy diagrame is shown below. What is $$E_a$$ for the reaction $$Q\, \rightarrow\, C\, ?$$
253327_17dd451bc7204bb3ae9699566ba16480.png
  • $$3 kcal$$ $$mol^{-1}$$
  • $$5 kcal$$ $$mol^{-1}$$
  • $$8 kcal$$ $$mol^{-1}$$
  • $$11 kcal$$ $$mol^{-1}$$
If the activation energies of the forward and backward reactions of a reversible reaction are $$E_a(f)$$ and $$E_a(b)$$, respectively. The $$\Delta E$$ of the reaction is ...........
  • $$E_a(F)-E_a(b)$$
  • $$E_a(F)+E_a(b)$$
  • $$E_a(F)=E_a(b)$$
  • $$-E_a(F)+E_a(b)$$
The rate of reaction increase by the increase of temperature because:
  • collision frequency is increased.
  • energy of products decreases.
  • the fraction of molecules possessing energy $$\geq\, E_T$$ (threshold energy) increases.
  • mechanism of a reaction is changed.
The reaction $$A\, \rightarrow\, B$$ follows first-order kinetics. The time taken for 0.8 mol of A to produce 0.6 mol of B is 1 hr. What is the time taken for the conversion of 0.9 mol of A to produce 0.675 mol of B?
  • 1 hr
  • 0.5 hr
  • 0.25 hr
  • 2 hr
The activation energy of reactant molecules in a reaction depends upon:
  • Temperature
  • Nature of the reactants
  • Collision per unit time
  • Concentration of reactants
What can you say about the existence of A if the potential energy diagram for the reaction
$$A\, \rightarrow\, B$$ looks like :
253320.jpg
  • A will exist
  • A will not exist
  • B will not exist
  • A and B are in equilibeium
In a certain reaction. $$10$$% of the reactant decomposes in one hour, $$20$$% in two hours, $$30$$% in three hours, and so on. The dimension of the velocity constant (rate constant) are:
  • $$hr^{-1}$$
  • $$Mol\, L^{-1}\, hr^{-1}$$
  • $$L\, mol^{-1}\, s^{-1}$$
  • $$Mol\, s^{-1}$$
For a hypothetical reaction: A + B $$\rightarrow$$ Products, the rate law is r = k[A]$$[B]^0$$. The order of reaction is:
  • 0
  • 1
  • 2
  • 3
A chemical reaction occurs as a result of collisions between reacting molecules. Therefore, the reaction rate is given by:
  • total number of collision occuring in a unit volume per second
  • fraction of molecules which possess energy less than the threshold energy
  • total number of effective collisions
  • none of the above
 $$k_1=X\:hr^{-1};k_1:k_2=1:10$$. Calculate $$\displaystyle  \frac{[C]}{[A]}$$ after one hour from the start of the reaction. Assuming only A was present in the beginning.

260349.png
  • $$\displaystyle \frac{[C]}{[A]}=\frac{10}{11}(e^{11x}-1)$$
  • $$\displaystyle \frac{[C]}{[A]}=\frac{10}{11}(e^{11x}+1)$$
  • $$\displaystyle \frac{[C]}{[A]}=\frac{10}{11}(e^{22x}-1)$$
  • $$\displaystyle \frac{[C]}{[A]}=\frac{10}{11}(e^{22x}+1)$$
The incorrect statement is:
  • all the collisions between reactant molecules do not lead to a chemical change
  • a zero order reaction proceeds at a constant rate independent of concentration or time
  • fast reactions have low activation energies
  • in a first order reaction, the reaction ideally takes finite time to be completed
A first order reaction has a rate constant $$1.5\times10^{-3}\:sec^{-1}$$. How long will 5.0 g of this reactant take to reduce to 1.25 g.
  • 924 sec
  • 462 sec
  • 1848 sec
  • none of these
The rate constant for a zero order reaction is $$2\times10^{-2}\:mol\:L^{-1}\:sec^{-1}$$, if the concentration of the ractant after $$25 sec$$ is $$0.25 M$$, calculate the initial concentration.
  • $$0.75 M$$
  • $$1.5 M$$
  • $$0.375$$
  • None of these
For a reaction $$\:A\overset{K_1}{\longrightarrow}B\overset{K_2}{\longrightarrow}C.$$ If the reaction are of $$1^{st}$$ order then $$\:\displaystyle\frac{d\left[B \right]}{d\,t}\:$$is equal to:
  • $$\;-k\left[B \right]$$
  • $$\;+k_1\left[A \right]$$
  • $$\;k_1\left[A \right]-k_2\left[B \right]$$
  • $$\;k_1\left[A \right]+k_2\left[B \right]$$
A substance undergoes first order decomposition. The decomposition follows two parallel first order reactions as  ; $$k_1=1.26\times10^{-4}\:sec^{-1}$$ and $$k_2=3.6\times10^{-5}\:sec^{-1}$$. Calculate the % distribution of B & C.   


260350.png
  • 77.7, 22.3
  • 22.3, 77.7
  • 67.7, 32.3
  • None of these
In a first order reaction the concentration of reactant decreases from 800 $$mol/dm^3$$ to $$50 mol/dm^3$$ in $$2\times 10^4 sec$$. The rate constant of reaction in $$sec^{-1}$$ is:
  • $$2\times 10^{4}$$
  • $$3.415\times 10^{-5}$$
  • $$1.386\times 10^{-4}$$
  • None of these
In a two step reaction, the rate determining step has the lowest energy of activation.
  • True
  • False
0:0:1


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