Small Amount of K

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elizabethrojas1G
Posts: 44
Joined: Fri Sep 25, 2015 3:00 am

Small Amount of K

Postby elizabethrojas1G » Mon Nov 09, 2015 11:15 pm

So in the course reader on page 127 it stated that since Kc was a really small value, we could assume that the concentrations would be unchanged. Why exactly is this value used as the "x" value?

Jonathan Shih 3H
Posts: 37
Joined: Fri Sep 25, 2015 3:00 am

Re: Small Amount of K

Postby Jonathan Shih 3H » Tue Nov 10, 2015 2:55 am

Hi!
I'm slightly confused as to what you're specifically asking, but I hope I can clarify and add some explanation as to the whole "x" variabe and how we can assume that it's essentially 0. We use a general variable "x" because honestly, it doesn't matter what variable we pick, as long as the variable is consistent. The same variable (in this case x) is used in the "change in molar concentration" row because the amount of change of each substance is reflective of the coefficients of the subtances within the balanced chemical equation. So to reach reach equilibrium (in this example with with product being formed, an amount "x" of the product is formed, with the respective ratios of the reactants being used to form the product. In this example, we can assume that the "x's" in the denominator can be assumed as insignificant (and thus to the value of 0) because the Kc value is extremely small, meaning that barely any product forms at equilibrium. This means that, again since the amount of product formed is proportional to the amount of reactants used, that to reach equilbrium, barely any reactant is used. In fact, the amount of reactant used is so small that by assuming the "x's" in the denominator are 0 (meaning that barely any reactant is subtracted from the original amount of reactant), the calculation itself is ultimately unaffected.
I hoped this helped, as I would like to again say that I was confused as to what your question was asking, but I hopefully explained the entire example as a whole relatively throughly.
-Jon Shih

elizabethrojas1G
Posts: 44
Joined: Fri Sep 25, 2015 3:00 am

Re: Small Amount of K

Postby elizabethrojas1G » Tue Nov 17, 2015 2:22 am

Thank you so much! You explained it really well, I get it now.


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