quadratic formula values

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Emily Tieu 2K
Posts: 38
Joined: Thu Jan 07, 2021 12:17 am

quadratic formula values

Postby Emily Tieu 2K » Sun Jan 17, 2021 11:11 pm

How do we know which x-value to choose from when both are positive values after computing the quadratic formula?

Simrah_Ahmed1J
Posts: 88
Joined: Wed Sep 30, 2020 9:49 pm

Re: quadratic formula values

Postby Simrah_Ahmed1J » Sun Jan 17, 2021 11:17 pm

If you've solved the equation right and there's two positive x values as a result, there should be one x value that is greater even than the initial concentration itself, and we know that would have to be wrong because if we're using it as a change we cant have the equilibrium concentration be negative.
So in short: the x value that is greater than the initial concentration is not the correct one.

Sofia Azmat 1I
Posts: 46
Joined: Fri Aug 30, 2019 12:16 am

Re: quadratic formula values

Postby Sofia Azmat 1I » Sun Jan 17, 2021 11:18 pm

When you have two positive values, I believe you pick the value that is less than what you see when you look at the initial concentration of the reactants, and reject the value that is greater than the initial concentration of the reactants.

Catie Donohue 2K
Posts: 93
Joined: Wed Sep 30, 2020 9:55 pm

Re: quadratic formula values

Postby Catie Donohue 2K » Sun Jan 17, 2021 11:22 pm

I believe Dr Lavelle said that you take that value that is smaller than the initial concentrations of reactants, because it wouldn't make sense for a product to increase by that higher X amount when there aren't enough reactants available to complete that reaction.

Adrienne Chan 1G
Posts: 87
Joined: Wed Sep 30, 2020 9:40 pm

Re: quadratic formula values

Postby Adrienne Chan 1G » Sun Jan 17, 2021 11:41 pm

Even though they both might be positive, Lavelle said only one of them will make sense when they're plugged into the equilibrium values. I just plug them into all of the values in the "E" row of the ICE table and it's always given me the right answer.

vuongnaomi1L
Posts: 97
Joined: Wed Sep 30, 2020 9:56 pm

Re: quadratic formula values

Postby vuongnaomi1L » Sun Jan 17, 2021 11:57 pm

if both are positive, choose the one that will not result in a negative number when you plug it in the equations for equilibrium constants. For example, if an equation to find the equilibrium concentration of a reactant is 0.5-x and you have values 0.2 and 0.8 from your quadratic equation, 0.8 will result in a negative concentration, so you would pick 0.2.

Lily Anne Garcia 1C
Posts: 80
Joined: Wed Sep 30, 2020 9:55 pm

Re: quadratic formula values

Postby Lily Anne Garcia 1C » Sun Jan 17, 2021 11:59 pm

no negative x values and if theyre both positive one will be bigger than the initial condition which isnt right

Teti Omilana 1G
Posts: 82
Joined: Wed Sep 30, 2020 10:05 pm

Re: quadratic formula values

Postby Teti Omilana 1G » Mon Jan 18, 2021 12:09 am

You shouldn't choose the one that is negative or that is too big to make sense in the context of the problem.

David Liu 1E
Posts: 85
Joined: Wed Sep 30, 2020 10:07 pm

Re: quadratic formula values

Postby David Liu 1E » Mon Jan 18, 2021 12:51 am

even though both are positive, only one should make sense given the conditions of the question

Yeonjoo Kim 2B
Posts: 14
Joined: Wed Sep 18, 2019 12:17 am

Re: quadratic formula values

Postby Yeonjoo Kim 2B » Mon Jan 18, 2021 11:44 am

You have to choose the positive x-value! If they're both positive, then you should try to plug them in to see if one of them results in a negative value.

jia207
Posts: 101
Joined: Wed Sep 30, 2020 9:52 pm

Re: quadratic formula values

Postby jia207 » Mon Jan 18, 2021 11:56 am

You would use the positive value for the answer to the question. If both are positive, choose what value makes sense for the question.

James Fu 2F
Posts: 10
Joined: Wed Nov 18, 2020 12:29 am

Re: quadratic formula values

Postby James Fu 2F » Sun Jan 24, 2021 11:36 pm

If there is one negative and one positive, only the positive one makes sense.

If they are both positive, only one of them should make sense so you'd find the pH and rule out the one that doesn't make sense.

RaniyaFeroz_1E
Posts: 84
Joined: Wed Sep 30, 2020 9:32 pm

Re: quadratic formula values

Postby RaniyaFeroz_1E » Sun Jan 24, 2021 11:38 pm

Try subtracting them from the initial molarity. If you get a negative output, then that one is not the correct answer.

LeahSWM 2E
Posts: 71
Joined: Wed Sep 30, 2020 9:47 pm

Re: quadratic formula values

Postby LeahSWM 2E » Sun Jan 24, 2021 11:40 pm

always go with the positive when presented with a negative and a positive. if both are positive you'll have to use both in further steps and see which one gives you a negative value.


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