Question

1.) The rate constant for a certain reaction is k = 3.40×10⁻³ s−1 . If the initial reactant concentration was 0.550 M, what will the concentration be after 20.0 minutes?

2.)A zero-order reaction has a constant rate of 1.10×10⁻⁴

M/s. If after 80.0 seconds the concentration has dropped to 9.00×10⁻²M, what was the initial concentration?

Answer 1

1) From the unit of the rate constant we can say that the reaction is a first order reaction

For a first order reaction,

C(t) = Co exp (- Kt)

where,

C(t) = Conc. at time t

Co = nitial Conc. = 0.55 M

K = Rate constant = 3.4 x 10^-3 s^-1

t = time = 20 min = 20 x 60 = 1200 sec

=> C(t = 1200 s) = 0.55 * exp (- 3.4 x 10^-3 x 1200) = 9.3 x 10^-3 M = Conc. after 20 minutes

2)

We know that for a Zero Order reaction,

C(t) = Co - Kt

where,

C(t) = Conc. at time t = 9 x 10^-2 = 0.09 M

Co = nitial Conc.

K = Rate constant = 1.1 x 10^-4 M / s

=> 0.09 = Co - (1.1 x 10^-4 x 80)

=> Co = 0.0988 M = Initial Conc.