CHEMISTRY COMMUNITY

Areli C 1L

Open book is pretty every resource you can lay your hands on. I don't think he will be using Respondus or another program to record us while taking the exam, so I think textbook, notes, and other instructional notes are all fair game for "open book." Thank goodness, the thought of using r...

Areli C 1L

Thank you! :)

Areli C 1L

Cumulative but for sure be ready for what we recently learned in class as that will definitely get you some points and everything else is fair game :)

Areli C 1L

I think what he meant for "time will not be an issue" is that you most likely won't need the full 4 hours to complete the 6 questions. If it is similar to my other exams, then once you start you have the full 4 hours of time and it automatically submits once your test time is over.

Areli C 1L

In his email, he did mention that the test-run will be happening today to make sure everything goes smoothly. I also wonder if it'll be multiple choice or fill in the blank with your answer.

Areli C 1L

I don't think K has units? thought it was unitless since its an EQ constant.

Areli C 1L

I feel like it'll be evenly spread out for the other topic but more focus on thermodynamics as we spent a lot of time on that. or if it itll be worth the most points. but as mentioned above review everything bit by bit, no cramming.

Areli C 1L

yup, as mentioned above, you would use Kelvin.

Areli C 1L

Congrats Rachana! Keep excelling! :D

Areli C 1L

Yes, it believes it would be deemed incorrect because if the electrons are unbalanced that means the charges don't cancel out even though the compounds themselves are equal. Just multiply it to get the common multiple and you'll be good. :)

Areli C 1L

Exactly! Stressing out or cramming at the last minute is never a good idea. It'll only increase anxiety ;(
-I know it does for me.

Areli C 1L

An element that is oxidized is a reducing agent, because the element loses electrons, and an element that is reduced is an oxidizing agent, because the element gains electrons.

Areli C 1L

For an acidic solution (which are much easier to undersand IMO) we'd use H+ to balance out the charges and OH- for redox reactions in a basic solution.

Areli C 1L

Yeah, I believe so, you'll have to multiply the coefficient with the charge to get the total charge for that one compound.

Areli C 1L

I think it doesn't just have to do with the number of moles, but with which reaction will be the strongest and thus produce the largest temperature change. Since b. has the highest molarity in the smallest volume, it will react the most (I think this is because the particle density is really high, ...

Areli C 1L

Because pH>pKa, the acid will mostly deprotonate. Since it deprotonates it will become the conjugate base, ChH3COO-. The conjugate base will have a net charge of -1. so was this question asking the charge of the conjugate base? I believe so, well as the above question mentioned it asked for the net...

Areli C 1L

Lara Kristine Bacasen 1L wrote:The problem should usually tell you if it is in an acidic (H+) or basic (OH-) solution.

That's what I was thinking?

Areli C 1L

Cathode is what is being reduced and the anode is what is being oxidized. Mind you these would be the half rxns for their corresponding part.

Areli C 1L

depends if the compound is gaining or losing electrons which you can identify by calculating the charge for each. Remember, LEO and GER :) Also Oxidizing agents and Reducting agents are not the compounds that are reduced or oxidized, but the ones that cause the oxidation or reduction for the other c...

Areli C 1L

you have to look at the charges. Once you locate the acid on the left, the conj. base will be the compound without the + charge or no Hand vice versa.

Areli C 1L

The second half of thermochemistry and then the following outline about electrochemistry.

Areli C 1L

I feel like usually, the problem would tell us the type of system it is along with the changes that have occurred: Melting, boiling, vaporizing, etc.

Areli C 1L

Yes, I believe they would equal 0 as no work or heat can be transfered.

Areli C 1L

This usually means that its an isothermal reversible reaction and that the internal energy is 0.
Id also suggest watching the Organic chemistry tutor on youtube as he has videos on thermodynamics!

Areli C 1L

Alondra wrote:Constant pressure: for monatomic it’s 5R/2; for diatomic it’s 7R/2

Constant volume: for monatomic it’s 3R/2; for diatomic it’s 5R/2

I addition to this, Organic Chemistry tutor has an entire video dedicated to this topic.

Areli C 1L

I think we would be expected to memorize the charges that appear most on the homework and any Lavelle includes during his lectures.

Areli C 1L

I believe in terms of dissociating 100%, we've only learned it through an aqueous state... so no need to worry about that now :p

Areli C 1L

I would agree that 10^-3 would be the cut-off, but that margin is so close. 10^-4 or 10^-5 would be a safer option. If you do decide to neglect x at 10^-3 always check at the end if your answer is withing 5%.

Areli C 1L

Honestly, I just try to memorize all the strong acids and bases(there aren't that many) also check if they dissociate completely. :)

Areli C 1L

Maia_Jackson_2C wrote:The rule is that the reaction will favor the side with less moles of gas for a volume decrease, you didn't mention gases so maybe the moles you counted weren't for gases?

This. Little details like these are the real kickers. Hope you figured it out OP.

Areli C 1L

Yeah, I believe we do. Everything on the first page of the learning outcomes but not the second.

Areli C 1L

As Ally Huang answered in another similar question, "At 100 degrees celsius, steam will produce a worse burn than boiling water because steam contains more heat energy than boiling water. It holds more energy than boiling water because it has the heat energy of boiling water and the heat energy...

Areli C 1L

Leila_4E wrote:This makes me really scared of steam now!

Hahah, still does a great job of relaxing the body during the quarter system!

Areli C 1L

As everyone previously mentioned I think Test 2 only focuses on topics discussed after the midterm. (not cumulative)

Areli C 1L

205405339 wrote:i would assume we are starting at 4A rn

I think so too because the reading introduces the calorimeter and heat capacity which we left off in class.

Areli C 1L

Depending on the units given, use the R constant that uses the same units in order for them to cancel and give the desired answer.

Areli C 1L

Timmy Nguyen Dis 1I wrote:we do not need to know that

Thank goodness. I was about to say.

Areli C 1L

If you can, draw a quick scale. If you add products, the scale will tip right and in order to regain equilibrium, the system will move to the left and vice versa.

Areli C 1L

Prasanna Padmanabham 4I wrote:It really depends on what information you are given, I feel like for most problems this is how I've been dealing with it...
1) convert pKa to Ka
Ka = 10^(-pKa)
2) write Ka concentration out and figure out [H+]
3) plug into pH = -log [H+]

I like this, clear and not too wordy :)

Areli C 1L

How do you all input the quadratic equation into the calculator without messing up? Is there a method to this madness of parenthesis?! :(

Areli C 1L

805097738 wrote:The UA's said the material would cover up to this friday's class material so I would focus of the first two weeks of information. The lecture videos that Lavelle posted cover a lot of the information and have great practice problems!

I forgot about his lecture videos! Nice :)

Areli C 1L

I'm not sure if Lavelle would structure his exams as he did 14A, but his tests were wickedly based on the homework. So, if you understand every single homework problem (Even the long complex ones) you will do awesome) :)

Areli C 1L

Qiu Ya Wu 4I wrote:Lavelle gives you 4 different values for the R constant on his formula sheet during tests. Whichever one you use depends on the units given in the problem.

Do you know if the problems will mention directly which R constant to use?(Like a given)

Areli C 1L

The units will be different and I don't think Lavelle will not mention the type of pressure (bar or atm) used in the problem. Either way, just be sure to maintain the units so you don't get points deducted.

Areli C 1L

Yes, if I'm not mistaken, I think Lavelle did mention that temp would be the only factor that changes the K eq.

Areli C 1L

Most likely it will be R=8.314 J/(K*mol) as it will be cancelled out with T= Kelvin. Also it probably will be given in our constant sheet on exam days.

Areli C 1L

Organic Chemistry Tutor! Great Youtube channel for chemistry help :)

Areli C 1L

I believe Prof. Lavelle mentioned it in class today. The gas law allows you to relate Pressure and Volume to concentration. You are then able to convert between partial pressures and concentration of a reactant in a reaction. [Conc.]=P/(RT)

Areli C 1L

From an earlier post, I learned that K is for a reaction that is at equilibria or the equilibrium constant. Q is calculated to determine where the reaction will proceed, Forward or Reverse since the rxn is not at equilibrium.

Areli C 1L

K describes the reaction once it reaches equilibrium. Q is calculated the same way as K, but it is for the reaction at any point in time that is not equilibrium. You can find Q and compare it with K to determine which way the reaction will proceed. Hope this helps. This makes so much sense! Thank y...

Areli C 1L

Why do chemists enjoy working with ammonia?
-Because it's pretty basic stuff.

Areli C 1L

I found this VSEPR Summary chart very helpful :)
https://www.studocu.com/en-us/document/george-mason-university/physical-chemistry-lab-ii/summaries/vsepr-summary/3958564/view

Areli C 1L

Mhm Looks good

Areli C 1L

I believe it does not matter whether they are bonded or not. Since its an intermolecular interaction H bond will be able to pair with any NOF atom.

Areli C 1L

It depends on the amount of lone pairs the central atoms has. This chart was helpful for me when trying to memorize them. Hopefully it appears. https://www.studocu.com/en-us/document/george-mason-university/physical-chemistry-lab-ii/summaries/vsepr-summary/3958564/view

Areli C 1L

Kristina Rizo 3K wrote:I know the bonds (sigma and pi), molecular shapes, bond angles and the intermolecular forces will be on test 2. I'm not sure if that is all though.

Do you know if we will be expected to memorize the bond angles?
I thought he mentioned in lecture that we weren't but maybe I didn't listen correctly.

Areli C 1L

Can someone provide some important concepts to keep in mind for test 2? I have the memory of a goldfish and I really want to do well on this test. Thank you!

Areli C 1L

Megan Ngai- 3B wrote:^ retweet

re-retweet

Areli C 1L

I think you can just say "bent" no matter if it is AX2E or AX2E2, but if asked to specify the electron geometry, you should state that it is trigonal planar for AX2E and tetrahedral for AX2E2. Hope this answer helps! Do you think we can specify all the names (Trigonal planar and tetrahedr...

Areli C 1L

Like those above me mentioned, it all depends on the amount of lone pairs and bonded pairs to the atom. Tetrahedral doesn't have any lone pairs, whereas the see-saw molecular shape does. :)

Areli C 1L

In case we aren't given it, it is best to know the trends from the periodic table. As we are given the Periodic table, just draw the trends directly on there for easy access.

Areli C 1L

Longer Bond=Weaker bond
Shorter Bond= Stronger bond
:)

Areli C 1L

April Meza 3K wrote:Here is an example of a dipole-dipole moment.

Thank you for providing a Visual. :) It is very helpful

Areli C 1L

So only 3 elements can partake in hydrogen bonding: Oxygen, Nitrogen, and Flourine.

Areli C 1L

Ah this one is the easiest :) From my understanding, all molecules will have London dispersion as an intermolecular force.

Areli C 1L

Does bond length also affect how strong the bond is? As Serena Siddiq said "The larger the radius of the atoms, the farther each of their centers are apart, and therefore, [they have a longer and weaker bond length than smaller radius atoms]. The smaller the radius of the atoms, the closer the...

Areli C 1L

From my understanding just those 3

Areli C 1L

yes ma'am :)

Areli C 1L

So first you have to use De Broglie's equation to solve for velocity since you can't just use the speed of light equation because the wavelength given is for an electron and not light. Then you would just use the photoelectric effect equation and plug in the values for work function and kinetic ene...

Areli C 1L

8. b) A newly designed laser pointer with a certain frequency is pointed at a sodium metal surface. An electron is ejected from the metal surface with wavelength of 1.10 nm. What is the frequency of the light from the laser pointer? The work function of sodium is 150.6 kJ∙mol-1. I am getting lost on...

Areli C 1L

The larger the shell gets the lower electronegativity the element will have because that larger outer shell's electron is a lot farther from the nucleus.

Areli C 1L

Yuri Lin 4H wrote:I think the rule of thumb is that the central atom is the least electronegative atom, not the one with the lowest ionization energy, though I might be wrong. Nitrogen has a lower electronegativity than oxygen, so it would be the central atom.

Thank you! I too was puzzled.

Areli C 1L

Basically they are highly reactive because they are desperately trying to gain a complete octet, so theyd try to grab it from anywhere.

Areli C 1L

When you draw a lewis structure you have to pay special attention to the valence electrons in each atom; they help determine if there are single/double/triple bonds. There is normally a center atom, and that is normally the atom that has the lowest ionization energy. For bonds (when the molecule is...

Areli C 1L

I've also looked into that but came back empty. :( As the others have said we only have the Video modules that show us past lectures of very similar (if not the same) problems from class itself.

Areli C 1L

I've definitely have been in your shoes before. If the reading feels a intimidating, you should watch some youtube videos first about the concept so you won't go in blind. After that, as you go back to the reading it will feel more familiar and less intimidating!

Areli C 1L

Thank you so much! This was quite insightful

Areli C 1L

Just be sure to know which elements are able to expand their octet so it doesn't mess up your lewis structure or cause confusion.

Areli C 1L

Adding on to what the post above me said, I believe Usually it is denoted by brackets and then the charge is placed at the top right corner. If it has a 2+ charge then its be a cation and vice versa.

Areli C 1L

Yes, it is a constant. Some prefer to write it as 3.00x10^8 or 2.998x10^8 believe it or not sometimes, depending on which one you use, it can change your answer slightly. So for accuracy try to use the 2.998x10^8. Then your final answer should be in the appropriate Sig figs :)

Areli C 1L

I try to prepare myself as much as possible, and try to get some sleep! Sleep is super important, or try to get little naps here and there so you don't feel like you're lacking.
(lord knows anxiety is a sleep killer).

Areli C 1L

I can't find my test grades on ccle, where do I go? I had the same problem, you should try to check your discussion section or go talk to your discussion TA if that doesn't work. I thought TA's were supposed to give our tests back, but the score itself isn't necessarily the grade we got because of ...

Areli C 1L

From my understanding, Avogadro's Number can be used to find Atoms, Molecules and Formula units of a compound. :)

Areli C 1L

As everyone else had mentioned, my TA also has only inputted homework assignments so far. Hopefully soon though!

Areli C 1L

If H20 is water, what is H204? Drinking, bathing, washing, swimming, etc. If H2O is the formula for water, what is the formula for ice? H2O cubed. Anyone know any jokes about the element sodium? Na. Have been trying to figure out the first joke for almost a year and I can't figure out lmao Hahah it...

Areli C 1L

Shreyesi Srivastava 2D wrote:Do you have 11 protons?
Cause you sodium fine

How have I never heard this one! HAHAh! :')

Areli C 1L

I have the 7th edition PDF if you want to use that one. I know some prefer the physical book, but that's expensive. Send me a Pm if you're interested, I'll gladly share it :)

Areli C 1L

Jarrett Peyrefitte 1L wrote:Try to make a list of reactants and products with their respective number of molecules and balance it one by one.

Yes! This simple list helps with confusion and knowing how much of what is on each side. I highly recommend this. :)

Areli C 1L

Speaking as someone who has taken 14A before and didn't do so well, Dr. Lavelle you really make these concepts so interesting and easy to understand. Your passion seeps through every lecture making your students feel as passionate to learn as you are to teach! Truly a one-of-a-kind professor :)

Areli C 1L

Wow, this is very helpful. Thank you :)

Areli C 1L

I think it would be best to show your work how you learned it rather than confusing yourself by adding minor steps. However, the minor steps might help you receive partial credit if your answer is incorrect. :)

Areli C 1L

From what I've been reading on the forums, our final answer should always be in the correct number of significant figures in order to be concise. So if the fewest number of sig figs in the problem was 4 then your final answer should contain only 4 sig figs.

Areli C 1L

Can we round to the least amount of sig figs that are allowed for each step in our calculation? So basically round at each calculation to 2,3 sig figs?

Areli C 1L

I would agree with everyone else, prefixes and suffixes are important to remember as it will also help you write out formula names given only the chemical formula. I'm pretty sure they'll give us a list of chemicals they'd want us to remember for the exam and maybe try to write the names of others i...

Areli C 1L

From what I've seen so far, grams/mole is equal to g.mol-1. Lavelle prefers us to write it as the latter since it makes canceling units simpler. I haven't seen g.mols though, so I wouldn't be able to explain the difference.

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