CHEMISTRY COMMUNITY

Yiyang Jen Wang 4G

Up to the first page of Outline 4: Thermodynamics.

Yiyang Jen Wang 4G

Delta U=0 for Isothermal compression or expansion (at constant temperature).

Yiyang Jen Wang 4G

At constant pressure w=-p delta V. Since delta H=delta U + p delta V=q+w+delta V=q+(-p delta V)+p delta V. So delta H=q.

Yiyang Jen Wang 4G

I think they have the same meaning and when a reaction is spontaneous it is favorable; and when a reaction is favorable it should occur spontaneously.

Yiyang Jen Wang 4G

Thank you!! I will ask TAs for help!

Yiyang Jen Wang 4G

Because work is defined as the energy transferred from one type to another whenever a force is applied causing an object to move a distance.Work would be the area under the graph on a force-displacement graph.

Yiyang Jen Wang 4G

Have the same questions!

Yiyang Jen Wang 4G

Was the answer key for test 1 posted? Will it be posted before the midterm? I didn’t do well and really need to review it for the midterm.

Yiyang Jen Wang 4G

At constant pressure

Yiyang Jen Wang 4G

If Delta H is negative, the reaction is exothermic, heat released; if Delta H is positive, the reaction is endothermic, heat absorbed.

Yiyang Jen Wang 4G

Ex: Delta H for CS2(l) + 3 O2(g) → CO2(g) + 2 SO2(g)? Given: C(s) + O2(g) → CO2(g); ΔHf = -393.5 kJ/mol S(s) + O2(g) → SO2(g); ΔHf = -296.8 kJ/mol C(s) + 2 S(s) → CS2(l); ΔHf = 87.9 kJ/mol Solve: C(s) + O2(g) → CO2(g), ΔHf = -393.5 kJ/mol 2 S(s) + 2 O2(g) → 2 SO2(g), ΔHf = 2(-326.8 kJ/mol) CS2(l) → ...

Yiyang Jen Wang 4G

In irreversible reactions, the reactants convert to products and the products cannot convert back to the reactants. An example of an irreversible reaction is combustion. In reversible reactions, the forward and reverse reactions occur simultaneously.

Yiyang Jen Wang 4G

Thank you for the definitions! So helpful!

Yiyang Jen Wang 4G

“The system is the part of the universe we wish to focus our attention on. In the world of chemistry, the system is the chemical reaction. For example: 2H2 + O2 ---> 2H2O The system consists of those molecules which are reacting. The surroundings are everything else; the rest of the universe. For ex...

Yiyang Jen Wang 4G

I think you could either skip the sections and do what we covered in lectures or read through the textbook and do the problems that we haven’t covered beforehand since all materials on the learning objectives will be on the midterms.

Yiyang Jen Wang 4G

I think it depends on the class average at the end of the quarter.

Yiyang Jen Wang 4G

Thank you for asking and thank you for the explanations!

Yiyang Jen Wang 4G

If the pressure of the reaction increased by adding inert gas(noble gas) there will be no effect on P&R concentration and no effect on the reaction.

Yiyang Jen Wang 4G

There isn’t any past exam questions for practicing unfortunately but the homework problems should definitely help.

Yiyang Jen Wang 4G

I think either “acid and base equilibria” or the topic that we are going to cover in Wednesday’s lecture should be fine.

Yiyang Jen Wang 4G

I would recommend to at least get familiar with most of them.

Yiyang Jen Wang 4G

You can approximate when K is less than 10^-3.

Yiyang Jen Wang 4G

K can be Kc (for concentration) or Kp (dealing with gas given the partial pressure). PV=nRT can be used to convert between Kc and Kp.

Yiyang Jen Wang 4G

We need pka to solve for pkb, and then we can rank the bases in order of strength. The larger the pka value : the smaller the pkb, the weaker the acid, and the stronger the conjugate base. Therefore ethylamine is the strongest base.

Yiyang Jen Wang 4G

I do not think we went over this concept in class so probably no need to worry about it.

Yiyang Jen Wang 4G

It is normally used to calculate the equilibrium constant K of a reaction. Or when K is given, it can be used to calculate one or more of the concentrations in the table that are unknown.

Yiyang Jen Wang 4G

You should put 3d before 4s since when 3d is filled it has lower energy than 4s.

Yiyang Jen Wang 4G

Last minute questions....How much do we need to know about the equilibrium for the upcoming final? :( I am so stressed out...

Yiyang Jen Wang 4G

Yes for PH sic figs count after the decimal

Yiyang Jen Wang 4G

Anyone know where to find any past exam questions for practicing? Really need to work on some actual problems!

Yiyang Jen Wang 4G

Just want to make sure... How much do we need to know about Ka, Kb, pKa and pKb for the upcoming final? Do we need to know how to calculate them? My TA mentioned in the section that we do not need to worry too much about them for this class since they will appear again in 14B...but they are on the s...

Yiyang Jen Wang 4G

Weak acids will have a higher pH value(lower concentration of hydrogen ions) than strong acids At the same concentration.

Yiyang Jen Wang 4G

They both talk about the same thing just with two different concepts, one based one proton and on based on electron. As an acid donates a proton, it can be also viewed as accepting an electron.

Yiyang Jen Wang 4G

Strong acids are fully ionised but weak acids are only partly ionised in solution. At the same concentration, weak acids have a higher pH value(lower concentration of hydrogen ions) than strong acids.

Yiyang Jen Wang 4G

I have the same question. I assume there will be more questions on week 6-10 materials but not sure.

Yiyang Jen Wang 4G

One or two I believe

Yiyang Jen Wang 4G

I think they are the same. Just depends on personal preferences.

Yiyang Jen Wang 4G

The sp2 bond would actually be more stable~

Yiyang Jen Wang 4G

I think you can just label the bonds with their names and draw them normally.

Yiyang Jen Wang 4G

I think since they will affect the shape of the molecules, they will also contribute in hybridization.

Yiyang Jen Wang 4G

Yes, they do. There are five d orbitals, referred to as dz2, dxy, dxz, dyz , and dx2-y2. The d orbitals are what give transition metals their special properties.

Yiyang Jen Wang 4G

No. I don’t think resonance would have any effect on VESPR.

Yiyang Jen Wang 4G

It depends on the distance between them. Since lone pairs are the closest to each other, they have the greatest repulsion strength.

Yiyang Jen Wang 4G

I don not think that we will be ask to draw the 3D models but we should definitely know their shapes, names, and angles between the bonds in each structure.

Yiyang Jen Wang 4G

One sigma bond for single, double, triple bond. One pi bond for double bond, and two pi bonds for triple bonds.

Yiyang Jen Wang 4G

According to our TA, Hybridization will not be on test 2. But the structures, shape, angles, and pi vs sigma bonds....will be on there.

Yiyang Jen Wang 4G

I believe it should say in the question which one to use. If not specified, either way should be fine.

Yiyang Jen Wang 4G

Yes! Lone pairs do count toward the number of electron densities! The F atom should have four regions of electron density.

Yiyang Jen Wang 4G

Both are fine, but sp3d is preferred.

See the answer here: viewtopic.php?t=1256

Yiyang Jen Wang 4G

KatherineValdez_4B wrote:so when you reach a d-orbital does it go before or after the previous s-orbital?

I believe both dsp3 or sp3d are okay but sp3d is preferred?
Here is the answer:
viewtopic.php?t=1256

Yiyang Jen Wang 4G

Only the orbitals need to be included so the answer should be sp sp2 sp3...

Yiyang Jen Wang 4G

In induced dipole, or London force, the dipole is created by the movement of electrons, causing a temporary dipole because one end is more negative than the other.

Yiyang Jen Wang 4G

I hope these will not be on the test or I would definitely fail.:(

Yiyang Jen Wang 4G

Longer bonds are easier to break. Shorter bonds are stronger since the attractions between the elements are stronger. Single bond is longer than double bond, and double bond is longer than triple bond. Therefore, single bond is weaker than double bond, and double bond is weaker than triple bond.

Yiyang Jen Wang 4G

ionic bond is usually between a metal and a nonmetal. Elements in ionic bonds donate and accept electrons (become ions) while in covalent bonds they share electrons.

Yiyang Jen Wang 4G

Elements in ionic bond donate and accept electrons while elements in covalent bond share electrons. The difference in electronegativity is also higher for ionic bond. Ionic bond is usually between a metal and a nonmetal.

Yiyang Jen Wang 4G

It just means that most elements prefer to have 8 valence electrons in order to stay stable. But many can have more or less than 8 especially when they bond to other elements.

Yiyang Jen Wang 4G

Thanks for asking!! I found this helpful as well!

Yiyang Jen Wang 4G

2.998*10^8 m/s is definitely more accurate, but 3.0*10^8 m/s is also not wrong for sure. If we can use a calculator then using the more accurate one is definitely more recommend.

Yiyang Jen Wang 4G

Yes, I believe we will get formula sheet and periodic table just like we had for the test.

Yiyang Jen Wang 4G

Since we haven’t really covered anything about chemical bonding in class, I believe that we should still do hw from the quantum world this week.

Yiyang Jen Wang 4G

N,L,M L determines shape/angular momentum
N=1, L=0 s
N=2, L=0 s, 1 p
N=3, L=0 s, 1 p, 2 d
N=4, L=0 s, 1 p, 2 d, 3 f

Yiyang Jen Wang 4G

You do not need to know how to draw! Although it might be really helpful if you can picture the orbitals in your head.

Yiyang Jen Wang 4G

Step Up session is definitely recommended! For me I think it is easier to just go and listen than read through the textbook~

Yiyang Jen Wang 4G

There's no universal notion of "up" or "down", they just represent the two directions. +/- is just for you to distinguish the difference between the two paired electrons. I believe it does not really matter which is which.

Yiyang Jen Wang 4G

It is possible that n can be larger and so that g orbital could exist, but since the electrons are so far away from the nucleus, the elements will be extremely unstable and will probably not exist under normal conditions. I don’t think we need to know that for the this class since it’s not even on t...

Yiyang Jen Wang 4G

Anybody knows whether Prof will post his lecture PowerPoint online or not? Where can I find it? I really need them for revising my notes! Thx

Yiyang Jen Wang 4G

Yeah I don’t think we need to know it for the text but it was really helpful at least for me to understand the concepts in this chapter.

Yiyang Jen Wang 4G

Our TA said in the discussion that you can post/reply from Monday to Sunday to get the points for the week.

Yiyang Jen Wang 4G

I think intensity is effected by amplitude. Higher amplitude will result in higher intensity which will cause the light to be brighter. But Plz correct me if I am wrong!

Yiyang Jen Wang 4G

I think professor mentioned in class that the perfect black body that can absorb all frequencies of light does not currently exist. Cuz if we can still see it, it must has reflected some sort of frequencies which are able to be detected by our eyes, or it will just be invisible. Plz correct me if I ...

Yiyang Jen Wang 4G

Textbook has a lot of readings and sometimes it is hard to distinguish what is really important from all the various concepts. However, the resources that the professor provided are extremely helpful for the course and homework. Highly recommend going over them and using textbook as a supplementary ...

Yiyang Jen Wang 4G

Study group will be so helpful! I felt like I’ve forgotten everything about chem:)

Yiyang Jen Wang 4G

Thank you so much for sharing these. I am a 2nd year right now and was so stressed about being a premed student. I felt like I have so much to do, to get prepared but don’t even know how to start. Your advices are so helpful! I should really make a plan for myself.

Yiyang Jen Wang 4G

I am not sure but I believe we will choose 5 questions for all the homework assignments in the future( from the weekly assigned topics) to turn in, but more practice is always highly recommend!

Yiyang Jen Wang 4G

As long as it is not a graphing calculator you will be all good I guess. Mine was TI36x pro, and I’ve used it for many other classes that say “ no graphing calculator” in their syllabus. :) however I am not 100% sure, I hope it will work for this class!

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