### 15.23?

Posted:

**Sun Mar 04, 2018 1:49 pm**In part C, why isn't [A]t going to be equal to .034? Why do we have to multiply it by two and then subtract that from the concentration of [A] 0 ?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=146&t=28842

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Posted: **Sun Mar 04, 2018 1:49 pm**

In part C, why isn't [A]t going to be equal to .034? Why do we have to multiply it by two and then subtract that from the concentration of [A] 0 ?

Posted: **Sun Mar 04, 2018 2:22 pm**

0.034 is the concentration in terms of B. You have the initial concentration in terms of A so you must convert [B] to [A] using the stoichiometric coefficients.

Posted: **Sun Mar 04, 2018 2:36 pm**

Just to clarify, in a reaction where 2A -> B + C, if B is increasing by 0.034 (assuming B initial = 0), then A must decrease by 0.034 * 2 since the reaction requires 2 A to be converted into B. As A initial = .134 and the change in A is -0.034 * 2, A at time t is .134 - 2 * 0.034.

Of course, C can be ignored.

Hope that makes sense

Of course, C can be ignored.

Hope that makes sense

Posted: **Mon Mar 05, 2018 5:44 pm**

On chegg part of the solution is written :

[A] = [A]* - ([B]/2)

[A] = (0.153)- 2(0.034) = 0.085

Why is the first part written as ([B]/2) ?

[A] = [A]* - ([B]/2)

[A] = (0.153)- 2(0.034) = 0.085

Why is the first part written as ([B]/2) ?