Determine the rate constant for each of the following fi rst-order reactions, in each case expressed for the rate of loss of A: (a) A S B, given that the concentration of A decreases to one-half its initial value in 1000. s; (b) A S B, given that the concentration of A decreases from 0.67 molL1 to 0.53 molL1 in 25 s; (c) 2 A S B C, given that [A]0 0.153 molL1 and that after 115 s the concentration of B rises to 0.034 molL1

Explanation:

The integrated first law is given by :

Where:

= initial concentration of reactant

[A] = concentration of reactant after t time

k = rate constant

a)

t = 1000 s

Solving for k:

The rate constant for this reaction is .

b)

t = 25 s

Solving for k:

The rate constant for this reaction is .

c) 2 A → B +C

According to reaction, 1 mole of B is obtained from 2 moles of A.

Then 0.034 mole of B will be obtained from:

of A

So, the concentration left after 115 seconds:

t = 115 s

Solving for k:

The rate constant for this reaction is .

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