For a first-order reaction, the half-life is constant. It depends only on the ra

Question

For a first-order reaction, the half-life is constant. It depends only on the rate constant k and not on the reactant concentration. It is expressed as

t1/2=0.693k

For a second-order reaction, the half-life depends on the rate constantand the concentration of the reactant and so is expressed as

t1/2=1k[A]0

Part A

A certain first-order reaction (Aproducts) has a rate constant of 6.90×103 s1 at 45 C. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration?

Express your answer numerically in minutes.

Explanation / Answer

first-order reaction (Aproducts)

k = (6.90*10^(-3)) s-1

K = 1/tln(a/a-x)

a = initial concentration = 100

a-x = final concentration = 6.25

(6.90*10^(-3)) = (1/t)ln(100/6.25)

t = timerequired = 401.8 sec

= 6.7 min

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