At a certain fixed temperature, the reaction below: A(g) 2B(g) AB2(g) is found to be first order in the concentration of A and zeroth order in the concentration of B. The reaction rate constant is 0.05s-1. If 2.00 moles of A and 4.00 moles of B are placed in a 1.00 liter container, how many seconds will elapse before the concentration of A has fallen to 0.30 moles/liter

34.7s elapse before the concentration of A has fallen to 0.30 M

Explanation:

A reaction that is first order follows the equation:

ln [A] = ln [A]₀ - kt

Where [A] is concentration of A (0.30M) in time t, and [A]₀ is initial concentration (2.00M). K is reaction rate constant (0.05s⁻¹).

Replacing:

ln [0.30] = ln [2.00] - 0.05s⁻¹t

t = 34.7s elapse before the concentration of A has fallen to 0.30 M

thats how its supposed to be