A first order reaction has a rate constant ...

NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

Question : 35 of 39

Marks: +1, -0

A first order reaction has a rate constant

1.15 \times 10^{-3} \mathrm{s}^{-1}

. How long will 5 g of this reactant take to reduce to 3 g?

Solution:

Here,

[R]_{0}=5 \, \mathrm{g}_{ ,}

[R]=3 \, \mathrm{g},

k=1.15 \times 10^{-3} \, \mathrm{s}^{-1}

For first order reaction,

t=\frac{2.303}{k} \log \frac{[R]_{0}}{[R]}

=\frac{2.303}{1.15 \times 10^{-3}} \log \frac{5}{3}

=2.00 \times 10^{3}(\log 1.667)

=2.0 \times 10^{3} \times 0.2219 \, \mathrm{s}

=443.8

=444 \, \mathrm{s}

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