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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: student8607 on January 31, 2009, 06:20:44 PM

Title: A better way?
Post by: student8607 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?
I got about 0.0183 molar

question 2: how many minutes does it take for concentration to drop to 0.0300M?
I got about 1 minute

question 3: how many minutes does it take for 20% to react?
I got about 90.4 minutes

Title: Re: A better way?
Post by: TheJoker 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

Title: Re: A better way?
Post by: student8607 on January 31, 2009, 09:03:51 PM

Ahhhh. I knew there was an equation for that.

Thanks!