Half-life of a radioactive element is 100yr. The time in which it disintegrates to 50% of its mass, will be

• 50 yr

• 200 yr

• 100 yr

• 25 yr

20% of a first order reaction was found to be completed at 10 a.m at 11.30 a.m. on the same day, 20% of the reaction was found to be remaining. The half life period in minutes of the reaction is

• 90

• 45

• 60

• 30

143.

The term (dc/ dt)in a rate equation refers to the

• concentration of the reactant

• decreases in concentration of the reactant with time

• increase in concentration of the reactant with time

• velocity constant of the reaction

If the rate expression for a chemical reaction is given by rate = k[A]^m[B]ⁿ

• the order of the reaction is m

• the order of the reaction is n

• the order of the reaction is m + n

• the order of the reaction is m- n

Unit of first order rate constant is

• mol L s

• mol^-1 L^-1 s^-1

• mol L^-1 s^-1

• s^-1 or min^-1

For a first order reaction, velocity constant, k =10^-3 s^-1. Two third life for it would be

• 1100s

• 2200s

• 3300s

• 4400s

The reaction 2NO₂(g) + O₂(g) $\rightleftharpoons$ 2NO₂(g) is of first order. If volume of reaction vessel is reduced to 1/3, the rate of reaction would be

• 1/3 times

• 2/3 times

• 3 times

• 6 times

For the functioning of enzymes which of the following statements is not correct?

• An optimum temperature is needed

• An optimum pH is needed

• They are substrate specific

• They always increase activation energy

A chemical reaction is catalysed by 'X', therefore, 'X'

• increases the activation energy.

• does not affect the equilibrium constant of the reaction.

• decreases the enthalpy of the reaction.

• decreases the velocity constant of the reaction.

The half-life of a radioactive isotope is 3 h. If the initial mass of the isotope were 256 g, the mass of it remaining undecayed after 18 h would be

• 8.0 gm

• 4.0 gm

• 12.0 gm

• 16.0 gm