3 replies to this topic

[spaceman]

I have the solution to this question but I still dont understand the steps. Please could someone talk me through it. It's driving me nuts not understanding it.
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Thank You

[Art Montemayor]

Space:

If you don't understand the steps leading to the solution (the algorithm), then how is it possible that you have the solution? How can you be sure it is the RIGHT solution?

Did you obtain the answer from some one else? If so, didn't you also obtain the steps required?

[kkala]

I have the solution to this question but I still dont understand the steps. Please could someone talk me through it. It's driving me nuts not understanding it.

Assume total volume does not change during reaction. Rate equation can be written dCa/dt=-kCa, where Ca=concentration of reactant A, getting less and less during reaction. Hence dCa/Ca=-kdt and integrating ln(CaFinal/CaInitial)=-kt. So in this case ln (1/10)=-kt and t=ln10/0.046 min = 50 min.

After that, read the steps of the "solution", they may be easier to understand.

Note: In case that you do not get the feeling of integration, assume Ca=100 mol/m3 at t=0, so at t=5 min it will be Ca=100-0.046*100*5=77 mol/m3. At t=10 min, Ca=77-0.046*77*5=59.3 mol/l, and so on (a spreadsheet is convenient). You will find that at t=45 min Ca has been 9.5 mol/m3, that is one tenth of original Ca (difference due to approximations). However the integral is normally calculated in the solution (not numerically).

Edited by kkala, 03 July 2010 - 06:22 AM.

[spaceman]

Space:

If you don't understand the steps leading to the solution (the algorithm), then how is it possible that you have the solution? How can you be sure it is the RIGHT solution?

Did you obtain the answer from some one else? If so, didn't you also obtain the steps required?

Hi Art,

Thank you for the fast reply. I took this question and answer straight out of a textbook. I just don't understand how they rearrange the equations. Is it just integration?