Positive X

[Jacqueline Vargas 3L]

Hi!

I can't remember if this was addressed during lecture but what do we do if more than one X we calculated is positive? Do we always have to plug in the positive x values into the equilibrium concentration expressions and see which one makes sense for concentration values (e.g. does not end up with a negative value for concentration)?

Thanks in advance!

[Devyn Chun 3I]

If you get two positive values for x, usually, if you plug both of the x values into the original equilibrium equations, only one of them will end up being positive. Choose the x value that makes a positive final concentration. We can't have negative equilibriums, so if you get a negative number when you plug in the x values, it probably isn't correct. Hope this helps!

[Akshat Katoch 2K]

You plug your X into the E part of the Ice table. If your answer is negative then that is not the X value we use because we can not have a negative concentration. Another way is to compare X to the initial value, if X is bigger you know your answer will be negative so the other X has to be the answer.

[elenadworak]

Yah, I've just looked to see that the initial concentration - X is positive.

[Lauren Wasef 3C]

You always choose the positive value for X!

[Maggie Messer 1A]

If both X's are positive, plug both into the ice table and one will give a negative value. The one that gives a positive value is the one you want to use. Usually the larger the X value is, the more likely it will create a negative value.

[Ainsley DeMuth 1H]

I ran into this problem on one of this weeks Achieve homework problems and was confused too. However, once I had calculated both values for X, only one of them made sense in the context of equilibrium values. While both x values may be positive values, one of these x values may not make sense in context and result in the equilibrium value being negative (ie when you subtract/compute using the equilibrium row in an ICE table). I would hope this is always going to be the case so you may just have to take the calculated x value one step further to figure out that only one makes sense by computation.

[Jessica Arcos 2H]

Usually when you get two positive values for x then you should choose the value that is smaller than the initial values on the ICE table. When I run into problems like these, one x value will always be bigger than the initial values.

[Symphony Jackson 3K]

Usually when I run into this problem, I can end up substituting the X into the equations in the ICE table and I only get one positive X value.

[Samir Panwar]

In the rare case that both values are positive, I would plug them back into the ICE table to figure out which one is positive and which one is negative. Since you can only have positive molar concentrations, it would be the one thats positive.

[14b_student 2E]

always chose the positive value for x!

[Arshaun Faraji 2H]

Plug both of them back in and you should only get one positive value. That is the one you should go with. :)

[N Kanuri 2E]

When using the quadratic formula, you'll almost always end up with two values, one that is right and one that is impossible. Check both values by plugging them back into your ICE table - if you get a negative equilibrium concentration for a substance, then that x-value isn't correct! The other time an x-value will be wrong is when it is negative. So pick the x-value that is positive and doesn't result in a negative equilibrium concentration value!

[tristenleem3B]

If both X are positive, you would plug both into the K equation and one of the equilibrium constants will be negative.

[Roxan Sheikh 3L]

You would just go with the positive value, or a value that isn't too high.

[Connor_Olsen_2K]

Simply plug them both in, only one will make sense in terms of the problem.

[erud]

The positive value for X is always correct!

[Mario Prado 1K]

Hello,

If you do happen to get two positive X values then you plug both into the equations. Usually one will then give you a negative value and you'll go with the positive one.

Hope this helps.

[Sophia Dominguez 3I]

When plugging in both positive values, typically one of them will result in a negative value because one of the X values will be greater than the initial. You want to steer away from the larger positive because it results in a negative value. Therefore, you will use the positive value that results in positive answers. You cannot have a negative value because there is no negative product or reactant in a chemical reaction.

[RJ Lopez 2l]

When you get two positive values for x, if you plug both of the x values into the original equilibrium equations, you will see that one of the value would result in a negative equilibrium. Choose the x value that makes a positive final concentration. negative equilibriums are incorrect, so if you get a negative number when you plug in the x values, it going to be the other value, usually the smaller one.

[Tristan Friet 3G]

If you substitute the X values back into the ICE equation, then you should get only one positive value.

[Andrew Yim 1K]

Hi,
Yeah, if you get two positive values, one will result in negative equilibrium concentrations when plugged into the equilibrium line of the ICE table.

[405825570]

Put both values into your ice chart, and only one will work (will be positive) :)

[Coraly De Leon]

Hello,
We will always want to use the positive value for X.

[SerenaSabedra]

Plug in both values of x into your ICE table, only one of them will end up being positive. This means it's the correct x because it is impossible to have a negative concentration.

[Lawrence Tran 2H]

Yes, you should see which one makes the most in the context of the reaction, so that you don't get a negative value of reactant or product

[Matthew Vu 3C]

If you get two positive values of x, only one should make sense. If when you subtract one of the values of x from the initial concentration you get a negative number, then it can't be this x because you can't have negative concentration.

[Anne Hogue 2J]

You should always use the positive value for x. If both of the values are positive, then plug them in as x and whichever one gives a positive answer is the one you use.

[Ashrita Singh 2F]

You should plug both values into the equations in your ice table, and it is likely that only one will remain positive.

[Lindsey Walter 3E]

Always choose the positive value for x, but if there is more than one positive x value, plus them back into the expressions in the e section of the ice table. This should leave you with only one set of plausible answers, which lets you know which x-value is the correct one to use!

[austinchun]

When both values are positive, you would plug both x values into the equations you created in your ICE table. Only one of the x values should make sense since the other x value would bigger than the initial concentration.