Question

For a first-order reaction, A → B, the rate coefficient was found to be 3.4 × 10-4 s-1 at 23 °C. After 5.0 h, the concentration of A was found to be 0.00018 mol L-1. What was the original concentration of A?

Answer 1

the original concentration of A = 0.0817092 M

Step-by-step explanation:

A reaction is considered to be of first order it it strictly obeys the graphical equation method.

`k_1 = (2.303)/(t)log (a)/(a-x)`

where;

k = the specific rate coefficient = 3.4 × 10⁻⁴ s⁻¹

t = time = 5.0 h = 5.0 × 3600 = 18000 seconds

a = initial concentration = ???

a - x = remaining concentration of initial concentration at time t = 0.00018 mol L⁻¹

`3.4 * 10^(-4)= (2.303)/(18000)log (a)/(0.00018)`

`3.4 * 10^(-4)= 1.27944 * 10^(-4) * log (a)/(0.00018)`

`(3.4 * 10^(-4))/(1.27944 * 10^(-4))= log (a)/(0.00018)`

`2.657= log (a)/(0.00018)`

`10^(2.657)= (a)/(0.00018)`

`453.94 = (a)/(0.00018)`

`a =453.94 * 0.00018`

a = 0.0817092 M

Thus , the original concentration of A = 0.0817092 M