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### Topic: A better way?  (Read 2664 times)

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#### student8607

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##### A better way?
« on: January 31, 2009, 06:20:44 PM »
first order reaction
rate constant at 427k: 5.11x10-5
initial concentration is 0.0340M

I know half life: 0.693/5.11x10-5 = 1,3561sec --> 3.7hour
Is there a method for solving these above questions or is it just about estimation of what you know?

question 1: what is the molarity after 2.00hour?

question 2: how many minutes does it take for concentration to drop to 0.0300M?

question 3: how many minutes does it take for 20% to react?

#### TheJoker

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##### Re: A better way?
« Reply #1 on: January 31, 2009, 06:47:16 PM »
you probably used this but just in case ,   for 1st order reactions:

ln([A]at time t / [A]initial ) = -kt

#### student8607

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##### Re: A better way?
« Reply #2 on: January 31, 2009, 09:03:51 PM »
Ahhhh. I knew there was an equation for that.

Thanks!