# NEET Chemistry Chemical Kinetics Questions Solved

BOARD

A first order reaction has a rate constant of 0.0051 min-1. If we begin with 0.10 m concentration of the reactant, what concentration of reactant will remain in solution after 3 hours?

Given : = 0.10 M,    t = 3 hrs = 180 min

K = 0.0051 min-1       [R] = ?

using formula : K =$\frac{2.303}{t}$log $\frac{\left[R{\right]}_{\circ }}{\left[R\right]}$

$\therefore$        0.0051 = $\frac{2.303}{180}$log $\frac{0.10}{\left[R\right]}$

or     log $\frac{0.10}{\left[R\right]}$ = $\frac{0.0051×180}{2.303}$

or   log $\frac{0.10}{\left[R\right]}$ = $\frac{0.918}{2.303}$ = 0.3986

or  log $\frac{0.10}{\left[R\right]}$ = antilog(0.3986)

or log $\frac{0.10}{\left[R\right]}$ = 2.503

$\therefore$           [R] = $\frac{0.10}{2.503}$ = 0.0399

$\therefore$ Concentration of reactant remains 0.040 M

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