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  4. A first order reaction has a rate constant 1.15 × 10-3 s-1 . How long will 5g of this reactant take to reduce to 3g ?

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Q. A first order reaction has a rate constant $ 1.15 \times 10^{-3} s^{-1} $ . How long will $5g$ of this reactant take to reduce to $ 3g$ ?

Chemical Kinetics

Solution:

Here,$\left[R\right]_{0} =5g,\left[R\right] =3g,k=1.15\times10^{-3} s^{-1} $
For first order reaction,$t=\frac{2.303}{k} lo\frac{g\left[R\right]_{0}}{\left[R\right]} $
$\frac{2.303}{1.15\times10^{-3}} log \frac{5}{3} =2.00\times10^{-3}\left(log 1.667\right)$
$=2.0\times10^{3}\times0.2219 s =443.8 \approx 444\, s$