14.33 Equation for the half-life of a 2nd order reaction


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Hannah Pablo 2H
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14.33 Equation for the half-life of a 2nd order reaction

Postby Hannah Pablo 2H » Sun Feb 22, 2015 5:54 pm

14.33 The half-life for the second-order reaction of a substance A is 50.5 s when [A]0 =0.84 mol/L. Calculate the time needed for the concentration of A to decrease to (a) one-sixteenth; (b) one- fourth; (c) one-fifth of its original value.

How do you obtain the equation to begin this problem?

Niharika Reddy 1D
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Re: 14.33 Equation for the half-life of a 2nd order reaction

Postby Niharika Reddy 1D » Sun Feb 22, 2015 7:20 pm

image.jpg
Half life for second order
At the half life, t1/2, half the initial concentration remains. Substituting this piece of information into the second order integrated rate law and solving for t gives the equation for the half life of a second order reaction.
Last edited by Niharika Reddy 1D on Sun Feb 22, 2015 7:21 pm, edited 1 time in total.

Neil DSilva 1L
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Joined: Fri Sep 26, 2014 2:02 pm

Re: 14.33 Equation for the half-life of a 2nd order reaction

Postby Neil DSilva 1L » Sun Feb 22, 2015 7:21 pm

On Prof. Lavelle's Constants and Equations, the last line gives the two relevant equations for this problem.
For second order reactions, use and (the sheet uses R instead of A, but I used A because that's what the solutions manual uses).

Rearrange the half-life equation to solve for k.

Then rearrange the first equation to solve for t. Replace with where is the concentration after the initial concentration has decreased to one-nth its original value.


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