# Chemical kinetics

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1. Jan 30, 2016

### krootox217

1. The problem statement, all variables and given/known data

If the concentration of A decreases 0.03 M in one hour, then the concentration of B should to, which means, [ B] should be 0.05 M?

And if I try to calculate k, i get 14.87 l/(mol*h)

For second order reactions, t1/2 sould be 1/(k*[A]0)

So I get 1.34 h as t1/2 for substance A, which somehow doesn't make sence, since more than 50% of the substance reacted in one hour. For B i get 9.29h, which doesn't make sence too. Can me someone tell my mistake?

2. Relevant equations
see above

3. The attempt at a solution
see above

Last edited by a moderator: Jan 30, 2016
2. Jan 31, 2016

### epenguin

If the concentration of A decreases 0.03 M in one hour, then the concentration of B should to, which means, [ B] should be 0.05 M? YES

I calculated the same rate constant as you.

Always good to check for reasonableness.

However I think that the simple relation of rate constant to half life only applies for the case of equal concentrations [A] = [ B]. ?

I am not sure there is any useful simple relation like that when these two are not equal. So I think you will have to work out each case using the full integrated rate equation, e.g. With [A]/[A0] = ½ and [ B] = [ B0] - [A0]/2 etc.

3. Jan 31, 2016

### krootox217

Ok, thanks for the answer, I found a way, where t1/2 for A yields 0.756h, which seems to make sence, at least for this reaction :)