Chemical Kinetics

Half-life of radioactive substance is 4 days . Amount of the substance decayed in two days is :

• $\frac{1}{\sqrt{2}}$

• 1 - $\frac{1}{\sqrt{2}}$

• 20 %

• $\frac{1}{8}$

Half-life pf a radioactive element is :

• 0.693

• $\frac{1}{0.693}$

• $\frac{0.693}{\mathrm{k}}$

• $\frac{\mathrm{k}}{0.693}$

Assertion : The kinetics of the reaction

mA + nB + pC → m'X + n'Y + p'Z

obeys the reaction as- $\frac{\mathrm{dx}}{\mathrm{dt}}$ = k[A]^m[B]ⁿ

Reason : The rate of reaction does not depend upon the concentration of C.

• 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.

For the reaction, 2N₂O₅ $\to$ 4NO₂+ O₂ rate of reaction is

• $\frac{1}{2}\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]$

• $2\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{N}}_2{\mathrm{O}}_5\right]$

• $\frac{1}{4}\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{NO}}_2\right]$

• $4\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{NO}}_2\right]$

For reaction aA → xP, when [A] = 2.2 mM, the rate was found to be 2.4 mM s^-1. On reducing concentration of A to half, the rate changes to 0.6 mM s^-1. The order of reaction with respect to A is

• 1.5

• 2.0

• 2.5

• 3.0

Assertion : According to transition state theory, for the formation of an activated complex, one of the vibrational degrees of freedom is converted into a translational degree of freedom.

Reason: Energy of the activated complex is higher than the energy of reactant molecules.

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

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

• If assertion is true, but reason is false.

• Both assertion and reason are false statements.

Which equation is correct for first order reactions ?

• t_1/2 $\propto$ C^-1

• t_1/2 $\propto$ C

• t_1/2 $\propto$ C^o

• t_1/2 $\propto$ C^1/2

87.5% decomposition of a radioactive substance complete in 3 hours. What is the half-life of that substance ?

• 2 hours

• 3 hours

• 90 minutes

• 1 hour

According to Hess's law, the heat of reaction depends upon :

• initial condition of reactants

• initial and final conditions of reactants

• intermediate path of the reaction

• end conditions of reactants

A reaction is catalysed by 'X' Here 'X' :

• decreases the rate constant of reaction

• does not affect the equilibrium constant of reaction

• decreases the enthalpy of reaction

• decreases the activation energy