Question about Chemical Equilibrium... from Berkley Review

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MedGrl@2022

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So I am going over the Equilibrium chapter in TBR... it is probably an older edition but I heard that the TBR books haven;t changed that much with the exception of the Organic Chemistry book.

Anyways, Chemical Equilibrium is a ratio right... [products]/[reactants]=K

so say that K=2 for A + B---> C

[C]=2, [A]=1, [B}=1... this works out

[C]=8, [A]=2, =2... also works out

also [C]=8, [A]=1, =4... works out too???

So as long as the concentrations satisfy the ratio determined by the equilibrium conditions at the set temperature is everything okay??? It seems weird that you can just change the concentrations to satisfy the equilibrium ratio.

Also, I was previously studying with EK and they did not go into as much detail as TBR... TBR has a lot of math too... is that good? Should I do the practice tests at the end of the chapter timed? 8 minutes per passage?

Thank you for all your help!

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So I am going over the Equilibrium chapter in TBR... it is probably an older edition but I heard that the TBR books haven;t changed that much with the exception of the Organic Chemistry book.

Anyways, Chemical Equilibrium is a ratio right... [products]/[reactants]=K

so say that K=2 for A + B---> C

[C]=2, [A]=1, [B}=1... this works out

[C]=8, [A]=2, =2... also works out

also [C]=8, [A]=1, =4... works out too???

So as long as the concentrations satisfy the ratio determined by the equilibrium conditions at the set temperature is everything okay??? It seems weird that you can just change the concentrations to satisfy the equilibrium ratio.


Yep, it always works out. Of course, if the stoichiometric coefficients are something other than one, that needs to be taken into account in the equilibrium expression as well.

Also, I was previously studying with EK and they did not go into as much detail as TBR... TBR has a lot of math too... is that good? Should I do the practice tests at the end of the chapter timed? 8 minutes per passage?

Is it good? Yeah, sort of. The MCAT isn't a math test. It's much more concerned that the student grasps concepts and is able to extract relevant information from a passage. However, it doesn't ignore the math altogether. You are expected to know how to manipulate equations and plug in numbers to arrive at the correct answer. But most of the math on the MCAT is relatively straightforward -- the math on TBR is much more convoluted than what you can expect to see come test day. Still, there's always a chance you could see a hate-filled question that would normally require a calculator, and TBR passages are good practice for that. I wouldn't be too concerned about properly timing yourself.
 
Yep, it always works out. Of course, if the stoichiometric coefficients are something other than one, that needs to be taken into account in the equilibrium expression as well.



Is it good? Yeah, sort of. The MCAT isn't a math test. It's much more concerned that the student grasps concepts and is able to extract relevant information from a passage. However, it doesn't ignore the math altogether. You are expected to know how to manipulate equations and plug in numbers to arrive at the correct answer. But most of the math on the MCAT is relatively straightforward -- the math on TBR is much more convoluted than what you can expect to see come test day. Still, there's always a chance you could see a hate-filled question that would normally require a calculator, and TBR passages are good practice for that. I wouldn't be too concerned about properly timing yourself.

In terms of calculation-intensive questions.. PS has been trending in that direction the past few years. Definitely be able to work with logs and scientific notation.
 
Yep, it always works out. Of course, if the stoichiometric coefficients are something other than one, that needs to be taken into account in the equilibrium expression as well.
.


So in my example A + B--->C

the concentration or partial pressure of A and B would have to be the same right? because the stiochiometric coeff is one for both of them. Indicating equal parts are necessary to create compound C, right?
 
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In terms of calculation-intensive questions.. PS has been trending in that direction the past few years. Definitely be able to work with logs and scientific notation.

Yeah... I remember from the past MCATs... usually they are easy equations but every now and then you will get something random that will blow you out of the water... :-/
 
So in my example A + B--->C

the concentration or partial pressure of A and B would have to be the same right? because the stiochiometric coeff is one for both of them. Indicating equal parts are necessary to create compound C, right?

Not necessarily. You could start with more of A than B..

Equal parts are necessary to create compound C but you may just have leftover A or B (think limiting reagents).
 
Not necessarily. You could start with more of A than B..

Equal parts are necessary to create compound C but you may just have leftover A or B (think limiting reagents).

But in the equilibrium equations [A]=, right? I mean there might be more of A in the environment of the reaction but the system will try to create an equilibrium where A + B--->C at K=2 (in my example at some defined temperature)

Also, if there is less of then it doesn't matter if [A] is in excess because there will not be enough to push the reaction toward product [C] right?

Please let me know if you think that I am understanding this correctly or not?
 
But in the equilibrium equations [A]=, right? I mean there might be more of A in the environment of the reaction but the system will try to create an equilibrium where A + B--->C at K=2 (in my example at some defined temperature)

Also, if there is less of then it doesn't matter if [A] is in excess because there will not be enough to push the reaction toward product [C] right?

Please let me know if you think that I am understanding this correctly or not?


A does not necessarily equal B.. look at your original post and you'll see that's true. The system just tries to create the ratio of 2, it doesn't 'care' whether A = B.

Yes, B would be the limiting reagent.. but you would still use the excess [A] in the equilibrium expression.

Think ICE tables.
Code:
                       A       +         B        ------>         C
Initial               5                3                           0 
Change                -x                 -x                       +x
Equilibrium          5-x                3-x                       x

So the change for A and B is equal.. but the concentration at equilibrium is not. To solve for x, you'd set the given Keq to the equilibrium expression.
 
A does not necessarily equal B.. look at your original post and you'll see that's true. The system just tries to create the ratio of 2, it doesn't 'care' whether A = B.

Yes, B would be the limiting reagent.. but you would still use the excess [A] in the equilibrium expression.

Think ICE tables.
Code:
                       A       +         B        ------>         C
Initial               5                3                           0 
Change                -x                 -x                       +x
Equilibrium          5-x                3-x                       x

So the change for A and B is equal.. but the concentration at equilibrium is not. To solve for x, you'd set the given Keq to the equilibrium expression.

I see... I may need to review this chapter more... so another question... partial pressures is like concentrations but for gases right?

like when determining the mole concentration for C(s)---> 2A(aq) + B(aq) it is Ksp=([2A]^2)() right? So for gases C(l)---> 2A(g) + B(g) it would be Kp=([2pA]^2)([pB])?
 
I see... I may need to review this chapter more... so another question... partial pressures is like concentrations but for gases right?

like when determining the mole concentration for C(s)---> 2A(aq) + B(aq) it is Ksp=([2A]^2)() right? So for gases C(l)---> 2A(g) + B(g) it would be Kp=([2pA]^2)([pB])?


Yup, partial pressures are the same thing when talking about gasses (and using Kp).
 
I also had a question for equilibrium: do we HAVE to know when to ignore the X-term? Will the MCAT seriously make us do quadratic equations? I always assumed that we can ignore it.
 
I also had a question for equilibrium: do we HAVE to know when to ignore the X-term? Will the MCAT seriously make us do quadratic equations? I always assumed that we can ignore it.

MCAT won't make you do quadratic equations. In fact, it's pretty unlikely you'll actually have to use an ICE table in the first place. These sort of questions are too time-consuming.

But you can most assuredly ignore the x term for anything MCAT-related.
 
MCAT won't make you do quadratic equations. In fact, it's pretty unlikely you'll actually have to use an ICE table in the first place. These sort of questions are too time-consuming.

But you can most assuredly ignore the x term for anything MCAT-related.

Are the TBR end of chapter practice passages like their practice MCATs? These problems are HARD and some are super calculation oriented. I already did all the AAMC practice exams and I am looking for good ones to practice with... someone recommended TBR exams... I want awesome practice without freaking myself out though... :-/
 
Are the TBR end of chapter practice passages like their practice MCATs? These problems are HARD and some are super calculation oriented. I already did all the AAMC practice exams and I am looking for good ones to practice with... someone recommended TBR exams... I want awesome practice without freaking myself out though... :-/

TBR is harder than AAMC in general. But you kind of want that harder for practice passages because it will really make sure you know the topic inside and out.

The TBR practice passages are also slightly harder than their FLs IMO. When you only have 7 questions to ask about a topic, you're not going to get as advanced as you can in 52 questions solely about that topic.
 
TBR is harder than AAMC in general. But you kind of want that harder for practice passages because it will really make sure you know the topic inside and out.

The TBR practice passages are also slightly harder than their FLs IMO. When you only have 7 questions to ask about a topic, you're not going to get as advanced as you can in 52 questions solely about that topic.

Thanks for all your help. I am getting my ass kicked on these equilibrium problems... I am so unfamiliar with ICE... EK did not go over it at all..

What do you think about TBR verbal in their full lengths? I am getting the PR hyperlearning book... should I just focus on that verbal... I have not tried TBR verbal but I haven't heard good things...
 
Yup, partial pressures are the same thing when talking about gasses (and using Kp).

Okay I am frustrated because I understand that only temperature can change Keq and Keq=[products]/[reactants] so that ratio must remain the same unless there is a temperature change.

However, if there is a pressure or volume change in a gas reaction then the reaction is shifted due to le chateliers principle. How does this not change the ratio? Does anyone have a good example?
 
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