CHEMISTRY COMMUNITY

Alyssa H

Zero-order reactions are linear because a change in any of the zero-order reactants' concentrations does not affect k.

Alyssa H

You can add/remove matter to/from the system, heat or cool the system, or compress a system (i.e. by use of a piston). I believe you can also let the system do work on its surroundings (i.e. releasing the piston and therefore releasing some pressure).

Alyssa H

Enthalpy (H) is defined as the heat absorbed/given off by a reaction. Entropy (S) is defined as the disorder of a system. Gibbs free energy (G) is defined as the maximum amount of non-expansion work that can be done within a closed system. The change in G can be found by multiplying the change in en...

Alyssa H

n represents moles, but specifically in this case, it represents the number of moles of electrons transferred per mole of reaction. This number would just be the number of e- transferred in the reaction.

Alyssa H

The Gibbs free energy of a system is the amount of non-expansion work that can be done on the system. Hence, why it is the maximum!

Alyssa H

"n" stands for moles. Oftentimes when dealing with redox reactions, n will simply be the number of electrons transferred in the reaction. This makes sense because this would represent the number of moles of e- transferred per mole of reaction!

Alyssa H

A closed system is one that essentially cannot let any substances within it out, but can exchange factors like temperature with its surroundings. However, an isolated system is a closed system that cannot exchange anything with its surroundings. For example, a water bottle left outside is a closed s...

Alyssa H

We typically use M in ice tables. As long as you have the moles of a reactant/product and the volume of the container, calculating M should be easy!

Alyssa H

Out of all factors we discussed that could change (volume, pressure, moles, etc.), K is only affected by a change in temperature. Typically, at least for now, the temperature will be either 25C or 298K, and I believe we're only supposed to have a conceptual understanding that K will change as temper...

Alyssa H

Q is the reaction quotient, meaning its value represents the reaction's current ratio of reactants to products. K is the reaction constant, and it is essentially the same as Q but represents the reaction at equilibrium. Both can be found using the same formula of [reactants]/[products].

Alyssa H

The R-value you will use for problems with the ideal gas equation depends on the units of the other terms in the equation. The different R-values and their units are laid out in the constants and equations sheet!

Alyssa H

I usually click on my profile name in the right corner (next to notifications) and then go to user control panel. You should be able to view all your posts under the "overview" tab! (There might be an easier way, but that's what I do :)).

Alyssa H

Yes, I believe those make up the bulk of the bond angles we need to know. However, I think it would be good to know when bond angles differ from those values-- we should only need to identify if an angle is > or < one of the "standard" angles.

Alyssa H

In a tetrahedral molecule, all the bond angles are 109.5 degrees!

Alyssa H

Every bond contains one sigma bond, and then one additional pi bond beginning with a double bond. So, a single bond contains one sigma bond, a double bond contains one sigma and one pi bond, a triple bond contains one sigma and two pi bonds, and so on.

Alyssa H

I believe pi bonds are weaker because there is less overlap between orbitals than in sigma bonds due to the parallel structure. The lack of overlap makes the bond easier to break.

Alyssa H

Molecules are considered bent or angular when there are two bonded atoms and one or two lone pairs on the central atom. This causes region(s) of electron density to form besides those created by the bonded atoms, which then pushes those bonded atoms further "down" and essentially "ben...

Alyssa H

H2O is bent/angular because the oxygen has two lone pairs, meaning there are four regions of electron density, but two bonded atoms.

Alyssa H

Lewis acids accept electron pairs, while Bronsted acids donate protons. Lewis bases donate electron pairs, while Bronsted bases accept protons.

Alyssa H

An easy way to determine the number of nodes is n-1. The 1s orbital has 0 nodes, 2s and 2p orbitals have 1 node, 3s, 3p, and 3d orbitals have 2 nodes, and so on.

Alyssa H

You can't determine what the radius is exactly just by looking at the periodic table, but you should know how to compare the relative sizes of atomic radii between elements. You CAN do this by looking at the periodic table!

Alyssa H

In lecture, Dr. Lavelle explained the use of prefixes bis-, tris-, tetrakis-, and pentakis- when the ligand in the compound you're naming has one of these prefixes: di-, tri-, tetra-, or penta-. I believe this is simply to avoid using the same prefixes within the same compound name and distinguishin...

Alyssa H

Since a Bronsted acid is able to donate H+, at least one hydrogen atom has to be in the molecular formula. Additionally, since a Bronsted base is able to receive H+, the substance needs to have an atom that can bond to that hydrogen atom. A good way to determine if a substance can accept an H+ is if...

Alyssa H

I know 14B and 14BL don't need to be taken at the same time, but is there a time limit on how far after 14B you can take 14BL?

Alyssa H

Hey! I'm from WA and have honestly never been so excited to see some rain. I don't have many plans for break yet, but I'm really looking forward to spending time with my dogs again, seeing my sister and my friends at home, and eating some home-cooked meals-- definitely missed those. I'm also so exci...

Alyssa H

Heyy :D I'm dealing with some major burnout this week, been doing a lot of final assignments for my classes as well as studying for final exams. All my finals are within the next couple of days, so I'm definitely very stressed! I am really looking forward to being back home in a week though, so can'...

Alyssa H

I believe you need a provable reason to opt out of the in-person exam, like a doctor's note, etc.

Alyssa H

OMG thank you for this-- I've been so curious about what he's playing lol he's got some funky taste

Alyssa H

I need a study guide made exclusively out of these LMAO-- then I'd actually want to study :')

Alyssa H

I believe posts are counted at the very end of the quarter, so as long as you have 50 by the end of this week (Week 10), you should be just fine!

Alyssa H

Heyy! Mine was so fun :D I was more than happy to see my two puppies, hang out with friends, and honestly just sleep in my own bed (I'm an out-of-state student and have been REALLY homesick!!). Plus, Thanksgiving dinner is probably the best meal of the year so that was sick. Hope all you guys had a ...

Alyssa H

Hey! I'm totally in the same boat-- adjusting to college life is tough, especially right after over a whole year of online high school. I'm personally struggling to regain my study habits and to take good care of myself since I tend to be a workaholic and often neglect my own well-being for the sake...

Alyssa H

I personally feel like it's a lot easier to work when I feel physically taken care of. For example, when I'm feeling burnt out I try to incorporate basic tasks into my set of goals, such as "take a shower," "eat lunch," or even "do my makeup" LOL. I feel like this makes...

Alyssa H

The Harry Potter series is a staple in my family, so I watch those when I'm feeling homesick. I also LOVE Greta Gerwig's Little Women, the story is a special one to me and I probably have seen it way too many times.

Alyssa H

If you're a sushi fan I recommend KazuNori!! They mainly do handrolls and their fish is so fresh, definitely one of my favorites when I'm feeling a bit fancy :D

Alyssa H

Maybe it's because yesterday was Thanksgiving and I'm about to eat some leftovers, but my mom's mac & cheese is one of my favorite comfort foods :')

Alyssa H

I've honestly had a difficult quarter and have not been doing as well as I know I can in my classes. This final feels like a HUGE deal, as it's my last opportunity to improve my grade in the class, and it's making me so stressed out. Any tips on how to take some of this pressure off myself and study...

Alyssa H

Unfortunately, I can't make next week's Wednesday lecture-- how quickly are they posted online? Just want to make sure I don't get too behind :)

Alyssa H

Isabella Nassir 2J wrote:HI,
I was wondering whether chem 14B will still have online recordings of the lectures in case we cannot be present for a lecture? Please let me know.

Thanks!

I would assume that lectures will still be recorded for 14B since Lavelle will still be the professor. I'm not totally sure though :').

Alyssa H

Intermolecular forces refer to those forces that are between molecules, and intramolecular forces refer to those forces that are within a molecule.

Alyssa H

The reason that COFH has a higher dipole moment than COF2 is because of the differences in electronegativity between bonded atoms. The negative pole in COFH is towards the oxygen and fluorine atoms, which are both much more electronegative than hydrogen. However, in COF2, the negative pole is toward...

Alyssa H

To figure this one out, I looked at the periodic table to compare the electronegativities of the outer atoms. For the first molecule, I noted that fluorine is more electronegative than oxygen, so it would be most likely that the negative pole would be towards the two fluorine atoms rather than the o...

Alyssa H

In this case, the bonds between oxygen and arsenic are each polar, but the entire molecule is not. Arsenic bonds with 4 oxygen atoms and has no lone pairs, meaning the molecule's shape is tetrahedral. Every bond angle is 109.5 degrees in a tetrahedral molecule, meaning it is symmetrical and the pola...

Alyssa H

Hi! You can identify sigma and pi bonds when looking at Lewis structures pretty simply. There is one sigma bond in every bond (single, double, triple, etc.), and then one pi bond for every additional bond past a single bond. For example, a single bond would just be one sigma bond, a double bond woul...

Alyssa H

The Roman numeral represents the oxidation state of the transition metal named before it. You can calculate the oxidation state of the transition metal by working out the charges of every other atom-- the difference between the total charge of those atoms and the total charge of the compound is the ...

Alyssa H

Ligands are ions/molecules that donate electrons to metal atoms and form coordination bonds. I believe they are also usually Lewis bases.

Alyssa H

I try to think of it like a game of tug-of-war! If electrons and protons are two teams, whenever one electron is added or subtracted, one "team" becomes stronger. When a cation is formed, an electron leaves its "team," so the protons can pull the electrons closer and make the ato...

Alyssa H

Like everyone's been saying, everything as of last Friday will be on the midterm. I believe Lavelle just sent out an email saying specifically everything covered through section 1E in the textbook.

Alyssa H

As this Friday's midterm comes up, I'm definitely dealing with the jitters :'). Something that makes me feel a lot more confident about taking tests is studying in set periods (for example, 30 minutes) and taking breaks to clear my mind and not get overly anxious. I feel the more I get stressed, the...

Alyssa H

Lavelle just sent out an email regarding test topics. He said this Friday's midterm will cover everything through the end of section 1E! Nothing from Week 4 will be on the test.

Alyssa H

Though m.s^-1 is the same as m/s, is either one preferred when writing units for our solutions?

Alyssa H

No two electrons in the same atom can have the same 4 quantum numbers. I think of the electrons' quantum numbers as sort of their "ID," as they are each described by their quantum numbers and we are able to identify them individually based on those numbers. Obviously, two electrons in diff...

Alyssa H

Wavelength and frequency are inversely proportional. Wavelength is the distance between two peaks/troughs in a given wave, and frequency is how often those peaks/troughs occur in a given unit of time (I believe it is generally 1 second). This means that if the distance between two peaks or troughs i...

Alyssa H

I totally agree!! I really struggle with focusing when I have to read a large amount of text in order to learn a new concept. Personally, listening to lectures and taking good notes before reading the book has helped with that, as I can come to the book with a better understanding and then simply ad...

Alyssa H

I've also heard that some of the textbook questions will be on the tests. Don't quote me on that but I think if so, it would definitely be useful to have done all the practice problems from the textbook!

Alyssa H

I think it would definitely be useful to know, especially if for some reason we get a question that asks what type of radiation corresponds to a certain wavelength we calculate. (Not sure if this will happen, but Lavelle asked our lecture yesterday so it might be a possibility!)

Alyssa H

Due to the law of conservation of mass, all chemical equations will be able to be balanced. However, like question 10 on last week's homework, sometimes not all reactants or products are included in the modeled equation or word problem because they're not necessarily important to the question. In th...

Alyssa H

Thanks Jason, I didn't learn much about sig figs in high school and the zeroes always confused me! This explanation is super helpful.

Alyssa H

My guess is we will not use Fahrenheit much because the SI unit for temperature is Kelvin (Celsius is also common), but if for some reason a question asks for a conversion the formulas are pretty simple. My guess is he just gave us the Celsius-Fahrenheit conversion for us Americans who don't use met...

Alyssa H

I believe we will also be given a formula sheet for tests (my TA mentioned something about this) which should at least include essential equations and a periodic table. My guess is we won't be given any chemical formulas on tests that we won't know or have access to, since the point of tests is to a...

Alyssa H

I believe 100.0 has 4 sig. figs as well, however, the last Achieve homework was a bit confusing! Question 4 said my answer was wrong when I sorted the number 200 into the "3 sig. fig." box, and said that it was actually 1 because the zeroes after the two are not significant. I'm almost 100...

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