Chemical Kinetics

A reaction , 2A $\to$ products (x) is found to follow zero order kinetics .Then :

• $\frac{\mathrm{dx}}{\mathrm{dt}}= \mathrm{k} \left[\mathrm{A}\right]$

• $\frac{\mathrm{dx}}{\mathrm{dt}}=\mathrm{k} [\mathrm{A}{]}^0$

• $\frac{\mathrm{dx}}{\mathrm{dt}} = \mathrm{k} [\mathrm{A}{]}^2$

• $\frac{\mathrm{dx}}{\mathrm{dt}} = \mathrm{k} \left[2\mathrm{A}\right]$

The rate of a reaction is primarily determined by the slowest step .This step is called :

• rate determining step

• reaction rate

• activation step

• None of the above

For a reaction, r= k(CH₃COCH₃)^3/2 then unit of rate of reaction and rate constant respectively is

• mol L-¹ s-¹, mol^-1/2 L^1/2 s-1

• mol^-1 L-¹ s^-1, mol^-1/2 L^-1/2 s^-1

• mol L-1 s^-1 mol^+1/2L^1/2s^-1

• mol L s, mol^+1/2 L ^1/2 s

If t_1/2  vs  $\frac{1}{{\mathrm{a}}^2}$ is a straight line graph then determine the order of reaction.

• Zero order

• First order

• Second order

• Third order

Energy of activation of forward reaction for an endothermic process is 50 kJ. If enthalpy change for forward reaction is 20 kJ then enthalpy change for backward reaction will be

• 30 kJ

• 20 kJ

• 70 kJ

• 50 kJ

Assertion : Rate of reaction doubles when concentration of reactant is doubled if it is a first order reaction.

Reason : Rate constant also doubles.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A radioactive substance decays $\frac{3}{4}$th of it original value in 2h. The half-life of the substance is :

• 1 h

• 30 min

• 20 min

• 15 min

The chemical reaction 2O₃ $\to$3O₂ proceeds as :

(I) O₃ $\rightleftharpoons$ O₂ + O (fast)

(II) O + O₃ $\to$ 2O₂ (slow)

The rate expression should be :

• r = k[O₃]²

• r = k[O₃]² [O₂]^-1

• r = k[O₃] [O₂]

• None of these

For a 1^st order reaction if concentration is doubled then rate of reaction becomes

• doubles

• half

• four times

• remains same

The first order rate constant for dissociation of N₂O₅ is 6.2 x 10^-4 s^-1 .The half-life period (in s) of this dissociation will be :

• 1117.7

• 111.7

• 223.4

• 160.9