Calculations using ice box

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Katie 1E
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Calculations using ice box

Postby Katie 1E » Wed Dec 06, 2017 2:54 pm

When you're using ice box and you are solving for the value of x and you get to the point where you have initial concentration minus x in the denominator of the equilibrium equation, how do you know when you can ignore the x? In what cases is the x negligible and how do you know? Sorry if this was confusing

Julia Meno 1D
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Joined: Fri Sep 29, 2017 7:04 am

Re: Calculations using ice box

Postby Julia Meno 1D » Wed Dec 06, 2017 3:14 pm

Usually if the equilibrium constant K is less than 10-3, the addition or subtraction of x to/from your initial value is negligible. But keep in mind that you can only "ignore" x when it is being added to or subtracted from a constant. In other words, if K < 10-3 and it is equal to (x)(x)/(1.00 - x), I can ignore the x in the denominator but not the x values in the numerator.

Ishan Saha 1L
Posts: 60
Joined: Fri Sep 29, 2017 7:03 am

Re: Calculations using ice box

Postby Ishan Saha 1L » Wed Dec 06, 2017 3:32 pm

You can also use the 5% rule, which states that if the value of x is less than or equal to 5% of the initial, then you can assume the equilibrium amount to be approximately the same value.

diangelosoriano
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

Re: Calculations using ice box

Postby diangelosoriano » Wed Dec 06, 2017 4:45 pm

Is there a time to use the 5% approximation versus using the value of K to determine if x is negligible?

Nha Dang 2I
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

Re: Calculations using ice box

Postby Nha Dang 2I » Thu Dec 07, 2017 4:39 am

Usually just seeing if K < 10-3 is sufficient, but if you want to be extra certain, you can use the 5% rule. I think either works.


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