Question

a) At a certain temperature, the rate constant for this reaction is 5.09× 10–4 s–1. Calculate...

a) At a certain temperature, the rate constant for this reaction is 5.09× 10–4 s–1. Calculate the half-life of cyclopropane at this temperature.

b) Given an initial cyclopropane concentration of 0.00190 M, calculate the concentration of cyclopropane that remains after 2.40 hours.

Homework Answers

Answer #1

from the units of the rate constant it is clear that it is first order

units for first order reaction is s-1

relation between rate constant and half life is

t1/2 = 0.693 / k = 0.693 / 5.09× 10–4 s–1 = 1.36 x 103

part B

formula for first order is

k = (2.303 / t ) x log[A0/A]

A0 = intial concentration which is given as 0.0019 M

A = concentration after 2.4 h

t = 2.4 h convert in to sec = 2.4 x 60 = 144 min x 60 = 8640 s

k = rate constant = 5.09× 10–4 s–1

plug in these values

5.09× 10–4 s–1 = (2.303 / 8640 s ) x log[0.0019 / A]

log[0.0019 / A] = 1.909

0.0019 / A = 101.909

0.0019 / A = 81.20

A = 0.0019 / 81.20

A = 0.0000234 or

A = 2.34 x 10-5 M

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