NEET Chemistry NEET PYQ-Chemical Kinetics

The half-life of a substance in a certain enzyme-catalyses reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg \[{{\text{L}}^{\text{-1}}}\] to 0.04 mg \[{{\text{L}}^{\text{-1}}}\] is [AIPMT (M) 2011]

A) 414 s

B) 552 s

C) 690 s

D) 276 s

Correct Answer: C

Solution :

[c] Enzyme-catalysed reactions follow first order kinetics.

\[\because \]Fall of concentration from 1.28 mg \[{{\text{L}}^{-1}}\]to

\[\text{0}\text{.04}\,\text{mg}\,{{\text{L}}^{-1}}\] involves five half-lives.

\[1.28\,\xrightarrow[{}]{{{T}_{1/2}}}0.64\xrightarrow[{}]{{{t}_{1/2}}}0.32\xrightarrow[{}]{{{t}_{1/2}}}0.16\]

\[\xrightarrow[{}]{{{t}_{1/2}}}0.08\xrightarrow[{}]{{{t}_{1/2}}}0.04\]

\[\therefore \]Time required \[=5\times {{t}_{1/2}}\]

\[=5\times 138\,s\]

= 690 s.