When can we decide to disregard x is the denominator of an equilibrium equation from an ICE table? ex) Ka= (x^2)/(0.137 - x)
When can we simply take x out of the denominator so the quadratic equation isn't necessary? Does it have to do with the value of Ka?
Thanks!
when x is small enough to disregard
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Re: when x is small enough to disregard
From my understanding, it has to do with the value of Ka or Kb, not the ICE table. When the exponent is greater than 10^-5 (i.e. 10^-7, 10^-10, etc), you can disregard the denominator (i.e. 0.05-x) and instead, it would just be 0.05. This was also talked about in one of the step-up sessions and that is how I understood it. Let me know if that makes sense or if I am thinking of it completely wrong LOL
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Re: when x is small enough to disregard
If the equilibrium constant is less than 10^-5, we can "disregard" x since the value of x will be so small it wouldn't make a significant difference in the equilibrium concentration.
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Re: when x is small enough to disregard
Whether we can disregard x depends on the value of Ka or Kb. If it is less than 10^-5, it means the reaction lies so much to the left (aka very little reactant gets converted to products) that the decrease in reactant concentration is not significant.
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Re: when x is small enough to disregard
I agree with the above posts. I want to add a way to check when in doubt if it appropriate to approximate by using percent ionization.
If the percent ionized is less than 5% than an approximation was appropriate, if not, it may be smart to redo the problem without approximation.
If the percent ionized is less than 5% than an approximation was appropriate, if not, it may be smart to redo the problem without approximation.
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