Ncert Exercises & Solutions

4.5: A first order reaction has a rate constant 1.15 10−3 s−1 How long will 5 g of this reactant take to reduce to 3 g?

From the question, we can write down the following information:

Initial amount = 5 g

Final concentration = 3 g

Rate constant = 1.15 10 $^{- 3}$ s $^{- 1}$

−1
We know that for a 1 $^{s t}$ order reaction,

$t = \frac{2.303}{K} \log \frac{{[R]}_{0}}{[R]}$
$= \frac{2.303}{1.15 \times 10^{- 3}} \times 0.2219$
$= 444.38 s$
$= 444 s (a p p r o x)$