Question

At a certain temperature the rate of this reaction is first order in HI with a rate constant of 0.0632 s
2HI g = H2 g + I2 g
Suppose a vessel contains HI at a concentration of 1.28M. Calculate how long it takes for the concentration of HI to decrease to 17.0% of its initial value.

Answer 1

Answer:

$28.037\ \text{s}$

Explanation:

$[A]_0$ = Initial concentration = 1.28 M

$[A]$ = Final concentration = $0.17[A]_0$

k = Rate constant = 0.0632 s

t = Time taken

For first order reaction we have the relation

$kt=\ln\dfrac{[A]_0}{[A]}\\\Rightarrow t=\dfrac{\ln\dfrac{[A]_0}{[A]}}{k}\\\Rightarrow t=\dfrac{\ln\dfrac{[A]_0}{0.17[A]_0}}{0.0632}\\\Rightarrow t=28.037\ \text{s}$

Time taken to reach the required concentration would be $28.037\ \text{s}$.