Rounding E Values in ICE charts

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Victoria Dao 3G
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Rounding E Values in ICE charts

Postby Victoria Dao 3G » Tue Jan 19, 2021 10:16 pm

Hi! I am still a little confused as to when we are allowed to round the E value in the ICE chart. What classifies a K value as being small enough that it won't affect the equilibrium concentration?

Ryan Laureano 3I
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Re: Rounding E Values in ICE charts

Postby Ryan Laureano 3I » Tue Jan 19, 2021 10:21 pm

If the K value is smaller than 1x10^-3 than you can ignore its effect when subtracting k from a concentration.

Megan Chan 3A
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Re: Rounding E Values in ICE charts

Postby Megan Chan 3A » Tue Jan 19, 2021 10:32 pm

Adding on to the previous reply, if you approximate by omitting x, you should also check that it is less than 5% of the initial concentration to make sure it is okay to approximate. Otherwise, the quadratic formula should be used to solve the equation.

MichaelRaad_1F
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Re: Rounding E Values in ICE charts

Postby MichaelRaad_1F » Tue Jan 19, 2021 10:57 pm

I think if k is smaller than 10^-5 then we can assume it is 0 when calculating equilibrium.

Darlene Lien 3E
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Re: Rounding E Values in ICE charts

Postby Darlene Lien 3E » Wed Jan 20, 2021 12:48 am

Hi, I believe Dr. Lavelle mentioned in the lectures that if K<10^-4 then the change in x is very small where it essentially becomes negligible, but I believe it could sometimes work when K<10^-3. Like the comment above said, a good rule of thumb is to use the 5% rule to check if the estimation works!

derickngo3d
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Re: Rounding E Values in ICE charts

Postby derickngo3d » Wed Jan 20, 2021 10:26 am

If the K value is less than 1.0 x 10^-3, then the x can be dropped.

Josh Chou 3K
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Re: Rounding E Values in ICE charts

Postby Josh Chou 3K » Wed Jan 20, 2021 1:53 pm

I think that if k < 10-3 (pretty sure Dr. Lavelle said k < 10-4 if you want to really be safe) and if the starting concentration(s) are more than 1000 times greater than the k value, you can estimate in the E row by omitting the +x or -x.

Eliana Carney 3E
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Re: Rounding E Values in ICE charts

Postby Eliana Carney 3E » Sat Jan 23, 2021 9:11 pm

Hey Victoria!
Basically, we are allowed to round the equilibrium value in an ICE chart when Kc < 1.0x10^-3.
One way to double check if rounding the equilibrium value in the ICE chart was appropriate is to make sure that the X value you calculated using the rounding is less than 5% of the initial concentration. If it is, the approximation was okay and if not you will have to do the full calculation for X without rounding.
Also, if you're not sure wether or not you're allowed to round, I usually don't round and just do the full calculation. It may not be very time efficient, but better safe than sorry. Hope this helps!

Kelly Ha 1K
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Re: Rounding E Values in ICE charts

Postby Kelly Ha 1K » Sat Jan 23, 2021 9:27 pm

If the K value is less than 1.0 x 10^-4 then the change in x (-x or +x) can be omitted. (I usually use 10^-4 rather than 10^-3 as the cutoff to be safe). Also, as stated in a previous post sometimes it's safer to just do the whole calculation without worrying about whether the approximation is valid just to make sure there are no errors, but this can depend on whether or not you're pressed for time.

Gustavo_Chavez_1K
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Re: Rounding E Values in ICE charts

Postby Gustavo_Chavez_1K » Sun Jan 24, 2021 5:46 pm

I remember in lecture Lavelle saying that if the k value is 10^-4 or smaller then x can be omitted in the E section of the ICE table.

Kiana Tashakori 1D
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Re: Rounding E Values in ICE charts

Postby Kiana Tashakori 1D » Sun Jan 24, 2021 5:58 pm

You can leave out x if the k value is equal to or less than 10^-4, because at that point k is so small that it wont really affect the values.

Arnav Saud 2C
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Re: Rounding E Values in ICE charts

Postby Arnav Saud 2C » Sun Jan 24, 2021 7:22 pm

If the K value is less than 1E-3, you can set the x values from the ICE tables to 0.

Brandon Gruender 3F
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Re: Rounding E Values in ICE charts

Postby Brandon Gruender 3F » Sun Jan 24, 2021 7:36 pm

Normally, anything smaller than 1x10^-4 is safe to assume, however I would always check that it is less than 5% of the initial concentration. If it is not then you need to use the quadratic equation to find x for that problem.

Colin Squire 3B
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Re: Rounding E Values in ICE charts

Postby Colin Squire 3B » Sun Jan 24, 2021 7:42 pm

When the equilibrium constant is less than 1x10^(-3), we can assume that they x value is negligible. Dr. Lavelle also showed us in lecture that if we calculate the percent ionization and it turns out to be less than or equal to 5%, we can use this "short cut."

305405193
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Re: Rounding E Values in ICE charts

Postby 305405193 » Sun Jan 24, 2021 10:22 pm

is this why he referenced it to money when he stated if someone has 10,000 dollars and gives 10 dollars to someone, they basically have 10,000 dollars? Is that what he signified, by basically rounding if the E is less than a certain value?

Annette Fishman
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Re: Rounding E Values in ICE charts

Postby Annette Fishman » Mon Jan 25, 2021 9:37 am

If the K value is less than 1.0 x 10^-3, then the x can be dropped. Lavelle prefers we drop it at 1.0 x 10^-4 to be more safe, but essentially its when the K value is so small it doesn't affect the overall concentration.

DMaya_2G
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Re: Rounding E Values in ICE charts

Postby DMaya_2G » Mon Jan 25, 2021 12:00 pm

The x can be dropped if the K value is less than 1.0 x 10^-3.

Nick Saeedi 1I
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Re: Rounding E Values in ICE charts

Postby Nick Saeedi 1I » Mon Jan 25, 2021 5:19 pm

If k is less than 10^-4 we can assume that x is very small so then we can round. Also, if the assumption is made, the percent ionization has to be less than 5 percent.


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