Question

The reaction 2A -> B is first order in A with a rate constant of 8.42 x 10-2 s-1 at 800oC. How long it will take for A to decrease from 5.00 M to 0.153 M?

Answer 1

41.4 s

Step-by-step explanation:

Given data

• Rate constant (k): 8.42 × 10⁻² s⁻¹ at 800 °C

• Initial concentration of A ([A]₀): 5.00 M

• Concentration of A at a time t ([A]): 0.153 M

Let's consider the following reaction of first order with respect to A.

2 A ⇒ B

We can find the time that it will take for A to decrease from 5.00 M to 0.153 M using the following expression.

`ln([A]/[A]_0)=-k.t\\ln(0.153M/5.00M)=-8.42 * 10^(-2)s^(-1) .t\\t = 41.4 s`