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

693.

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

For a reaction; A + B  product, it was found that rate of reaction increases four times if concentration of 'A' is doubled, but the rate of reaction remains unaffected if concentration of 'B' is doubled. Hence, the rate law for reaction is :

• rate = k[A][B]

• rate = k[A]²

• rate = k [A]²[B]¹

• rate = k [A]²[B]²

For the reaction :

H₂ + Cl₂ $\stackrel{\mathrm{Sunlight}}{\to }$ 2HCl , the order of reaction is :

• 0

• 2

• 1

• 3

The rate constant k, for the reaction 

${\mathrm{N}}_2{\mathrm{O}}_{5\left(\mathrm{g}\right)} \to 2{\mathrm{NO}}_{2\left(\mathrm{g}\right)} +\frac{1}{2}{\mathrm{O}}_{2\left(\mathrm{g}\right)}$ is 2.3 x 10^-2s^-1. Which equation given below describes the change of [N₂O₅] with time? [N₂O₅]₀ and [N₂O₅]_t correspond to concentration of N₂O₅ initially and at time t.

• [N₂O₅]_t =[N₂O₅]₀ +kt

• [N₂O₅]_t = [N₂O₅]₀e^kt

• log[N₂O₅]_t = log[N₂O₅]₀ +kt

• $\ln \frac{[{\mathrm{N}}_2{\mathrm{O}}_5{]}_0}{[{\mathrm{N}}_2{\mathrm{O}}_5{]}_{\mathrm{t}}}= \mathrm{kt}$

For the reaction A + 2B → C, the reaction rate is doubled, if the concentration of A is doubled. The rate is increased by four times when concentrations of both A and B are increased by four times. The order of the reaction is

• 3

• 0

• 1

• 2

The increase in rate constant of a chemical reaction with increasing temperature is (are) due to the fact(s) that

• the number of collisions among the reactant molecules increases with increasing temperature

• the activation energy of the reaction decreases with increasing temperature

• the concentration of the reactant molecules increases with increasing temperature

• the number of reactant molecules acquiring the activation energy increases with increasing temperature

Identify the correct statement from the following in a chemical reaction.

• The entropy always increases

• The change in entropy along with the suitable change in enthalpy decides the rate of reaction

• The enthalpy always decreases

• Both the enthalpy and the entropy remain constant

Which one of the following is wrong about molecularity of a reaction?

• It may be whole number or fractional

• It is calculated from reaction mechanism

• It is the number of molecules of the reactants taking part in a single step chemical reaction

• It is always equal to the order of elementary reaction