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

`28.037\ \text{s}`

Step-by-step 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([A]_0)/([A])\\\Rightarrow t=(\ln([A]_0)/([A]))/(k)\\\Rightarrow t=(\ln([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}`.