The Only Prep You Need

Chapter 4: Phases and Phase Equilibria

Re: Chapter 4: Phases and Phase Equilibria

This is regarding GEN CHM Chapter 4 Worked Solution Question 29:

Could you please kindly make clear which is a superscript and which is numerator and denominator as I am a bit confused about explanation for this conversion.

Regards,
Ania
horbowiec.7527

Posts: 71
Joined: Mon Mar 08, 2021 11:35 am

Re: Chapter 4: Phases and Phase Equilibria

horbowiec.7527 wrote:This is regarding GEN CHM Chapter 4 Worked Solutions Question 20 (CHM-110)

Since we always use SI units I have used Kelvin not "degree" for my unit of temperature...
I ended up with R = Joules/(mol)(K)

Why would you use degree over K and why mol times degree = mol/K?

You are correct to use kelvin, the Kelvin scale, K, and not degree.

You are also correct to get here:

R = Joules/(mol)(K)

... but it appears that you do not like to see this:

R = Joules/(mol)(K) = Joules/(mol)/(K)

I understand that you are looking at mol/K and it seems impossible because we just had (mol)(K). Well, the problem is perspective and the order of operations. Remember that according to your equation, K must be in the denominator, so we can do the following:

R = Joules/(mol)(K) = Joules/(mol) x 1/(K) = Joules/(mol)/(K) = Joules/(mol)(K)

Why does it look strange? Because mol is the denominator for Joules but is never the numerator for K.

An example: 15/5/2 = ?

(15/5)/2 = 3/2
15/(5 x 2) = 15/10 = 30/20 = 3/2

BUT

15/5/2 = is NOT = 15/(5/2) = (15 x 2)/5 = 30/5 = 6

Consider revising GM 1.4.2.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

horbowiec.7527 wrote:This is regarding GEN CHM Chapter 4 Worked Solution Question 29:

Could you please kindly make clear which is a superscript and which is numerator and denominator as I am a bit confused about explanation for this conversion.

Done!
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

horbowiec.7527 wrote:This is regarding GEN CHM Chapter 4 Worked solution question 27 (CHM-113)

I am a bit confused by this question. I have chosen B as being not consistent with the graph and because of that I didn't even consider answer D.

Explanation for B feels wrong to me... it appears that X rays end just before hitting 0.001 g/m^3 level of atmospheric density but choice B in question states atmospheric density of 10^-4 g/m^3 by X rays = 0.0001 g/m^3 and X rays are reaching that level so likely to affect it? Am I not understanding something here?

Actually, you understand it correctly and you chose the correct answer. Please return to the worked solution tomorrow for confirmation.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

Do PLOW and THIGH refer to ideal gases or real gases? In the textbook page on CHM-95, it says this is for ideal gases however the "New: Deviation from the Ideal Gas Law" video says this is for real gases.
dosani.rk7379

Posts: 7
Joined: Sun Dec 13, 2020 9:49 am

Re: Chapter 4: Phases and Phase Equilibria

Could someone please explain Question 15 about real and ideal gases, specifically how and why A, B and D are incorrect and how C is correct? Thank you!
dosani.rk7379

Posts: 7
Joined: Sun Dec 13, 2020 9:49 am

Re: Chapter 4: Phases and Phase Equilibria

dosani.rk7379 wrote:Do PLOW and THIGH refer to ideal gases or real gases?

Both real gases AND ideal gases behave ideally at PLOW and THIGH. However, ideal gases also behave ideally outside of those parameters.

dosani.rk7379 wrote:In the textbook page on CHM-95, it says this is for ideal gases however the "New: Deviation from the Ideal Gas Law" video says this is for real gases.

If you have PLOW and THIGH then you have ideal gas conditions irrespective of the gas being real or ideal.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

goldstanda3269 wrote:
dosani.rk7379 wrote:Could someone please explain Question 15 about real and ideal gases, specifically how and why A, B and D are incorrect and how C is correct? Thank you!

First, this question can be answered because of the passage. The first 2 paragraphs establish the condition for ideal gases. In the first paragraph, it states "they have mass". So the only question is: Do normal (real) gases have mass? And of course they do! That is why, for example, we can calculate the molecular weight of oxygen (O2) and nitrogen (N2) which are the two gases that make up 99% of air. On this basis, the answer is C.

Also, as the worked solution mentioned, since gas particles have kinetic energy (which is 1/2 mass x v^2), they must have mass.

CHM 4.1.2 and the videos go over the theory which is not really so important to commit to memory for GAMSAT purposes.

Nonetheless:

A is incorrect because paragraph 1 says "occupy no space" but of course every single atom in the universe occupies space (we have seen images of their shapes in earlier chapters).
B is incorrect because paragraph 1 states "no attractive or repulsive forces" but CHM 4.2 shows how real gas molecules can be attracted to each other because of charge differences (of course, opposite charges attract whether they are permanent like ions, or temporary like diatomic gases H2, Cl2, etc).
D is incorrect because real atoms and molecules bounce off of container walls (that's how we measure pressure) and bounce off each other in largely elastic collisions.

I would not take a theory question (no graphs, no calculations, no layered reasoning) too seriously. You might get 1-2 like this out of 75 exam questions in Section 3.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

Hi there,

1. In relation to Question 11, could you please re explain to me how you got A 'the total neutral density' as the answer? I am a little bit confused even after looking at the worked solutions.

2. In relation to Question 15, I was under the impression that 'real gases possess mass' however the answer says that it is incorrect?

3. In relation to Question 17 and 18, how do you determine these answers? I have had a look at the worked solutions however I am still unsure and need some assistance.

Thank you so much,

Kind regards and best wishes,

Em Stevens
emstevens46670

Posts: 15
Joined: Fri Mar 19, 2021 4:02 pm

Re: Chapter 4: Phases and Phase Equilibria

emstevens46670 wrote:1. In relation to Question 11, could you please re explain to me how you got A 'the total neutral density' as the answer? I am a little bit confused even after looking at the worked solutions.

Please have a look at the worked solution again tomorrow. We will embed a video from a tutorial discussing that question so hopefully you will find that helpful.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

emstevens46670 wrote:
2. In relation to Question 15, I was under the impression that 'real gases possess mass' however the answer says that it is incorrect?

As you have seen, the great majority of GAMSAT-style questions do not rely solely on assumed knowledge, this is a rare one so it should not be taken too seriously.

Basically, both real gases and ideal gases have mass. So if they both have mass, it does NOT contribute as a factor to distinguish real from ideal (that is why C is the only correct answer).
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Re: Chapter 4: Phases and Phase Equilibria

emstevens46670 wrote:
3. In relation to Question 17 and 18, how do you determine these answers? I have had a look at the worked solutions however I am still unsure and need some assistance.

We uploaded a new version for the worked solution for question 17, please let us know if it is helpful.

Question 18: This is basic graph analysis (GM 3.5, slopes). The worked solution provides additional examples. In order to help, please provide a specific part of the solution which is not clear for you.
goldstanda3269

Posts: 1719
Joined: Wed Aug 25, 2010 10:59 pm

Previous

Return to Masters Series GAMSAT Section 3 General Chemistry

Who is online

Users browsing this forum: No registered users and 1 guest