CHEMISTRY COMMUNITY

Moura Girgis 1F

Since units ALWAYS have to match with the other units given in the equation/ formula, you would have to convert.

Moura Girgis 1F

Cp in the specific heat capacity formula stands for constant pressure, since the delta T in that formula is what stands for a change in temperature.

Moura Girgis 1F

N is determined by the number of electrons being transferred, which can be calculated by canceling out the number of electrons in a reaction so that the total charge in reactants equals the total charge of the products.

Moura Girgis 1F

A salt bridge basically facilitates the transfer of electrons from the anode to the cathode so that neither side has any charge build-up. It ultimately keeps the solution neutral within the galvanic cell.

Moura Girgis 1F

That's right, since the loss of electrons occurs through oxidation, the process is carried out in an anode, while the gaining of electrons occurs through reduction, which is carried out in a cathode.

Moura Girgis 1F

This equation is on the constants and equations sheet that we could use for tests, but we didn't really cover it in lecture.

Moura Girgis 1F

Yes, it would be the opposite for an exothermic reaction, as when the temperature increases, the reaction favors the products and shifts to the right, resulting in an increase in K.

Moura Girgis 1F

SamayaJoshi1A wrote:How do catalysts affect activation energy?

Catalysts lower activation energy so the reaction occurs at a faster rate.

Moura Girgis 1F

Chad's Chemistry videos are so helpful when trying to get a different perspective while learning basic concepts!

Moura Girgis 1F

It is only when they are in the overall rate law that the reactants are involved in the slow step.

Moura Girgis 1F

It ultimately depends on the units. 8.314 tends to be used for energy problems which deal with joules, while 0.08206 is used for problems with volume, moles, pressure, or temperature.

Moura Girgis 1F

Although the magnitude tends to be different, since it's dependent on the reaction, K is positive because it's the rate.

Moura Girgis 1F

If you take the sum of the orders of all the elementary reactions you can calculate the overall order.

Moura Girgis 1F

F is an electrophile while F- is a nucleophile. F needs an electron while F- has an extra one.

Moura Girgis 1F

Definitely not all, but I'm sure it'll be a good percentage of them.

Moura Girgis 1F

A change in temperature is a factor that would affect k

Moura Girgis 1F

Rate constants tend to always be positive since they are dependent on concentration, and concentration is always a positive value.

Moura Girgis 1F

Also, we do not have to memorize this constant, as it is on the constants/equations sheet Dr. Lavelle made for us

Moura Girgis 1F

Shark wrote:which youtube channels would you recommend?

Khan Academy and The Organic Chemistry Tutor on YouTube have been really helpful for me!

Moura Girgis 1F

As T increases, so too does K. As a result, increased T leads to more activation energy as a result of more collisions.

Moura Girgis 1F

That's right, Le Chatelier's Principle only applies to gases.

Moura Girgis 1F

Percent deprotonation is used for acids [H+] and percent protonation is used for bases [OH-]

Moura Girgis 1F

Here's a link with the string acids and bases which should be memorized:

https://www.trentu.ca/online-legacy/mod ... _Bases.pdf

Moura Girgis 1F

That would be Gibbs free energy equation in which (change in Gibbs free energy) is equal to (change in enthalpy) minus (temperature in Kelvins times change in entropy).

Moura Girgis 1F

It would not be at equilibrium when changing phase, only once the process is complete.

Moura Girgis 1F

You could also consider taking chem BL in summer if you don't want to take it with 14 C in spring.

Moura Girgis 1F

A difference between the two is that enthalpy tends to be negative, as there is a change in heat, while entropy tends to be positive, as there is a change in disorder.

Moura Girgis 1F

a phase change is any change between the states of matter. This includes solid to liquid, liquid to gas, solid to gas, or vice versa.

Moura Girgis 1F

vapor and gas are pretty much the same thing

Moura Girgis 1F

Enthalpy is a state property that measures heat, whereas heat is the flow of energy

Moura Girgis 1F

vuongnaomi1L wrote:I actuallly dont read the textbook and whenever I have a question I either ask the UA's or go to the professor's office hours.

Same here, I feel like watching videos as well about the same concepts gives me a better understanding that just reading about it from the textbook.

Moura Girgis 1F

I took AP chemistry back when I was a sophomore in high school and am now taking 14A as a freshman in college so I understand how frustrating it is to forget the majority of the chemistry once learned. One tip I would have is to finish all the modules Dr. Lavelle posted on his website and also bree...

Moura Girgis 1F

There is no reset button, but you could try taking a screenshot of the question before solving it so that when you wanna go back and solve it again, you can find the question without it having been answered.

Moura Girgis 1F

For anyone who ordered their textbook from the UCLA store and already received it, was it a physical copy? and if so, did it include an access code for sapling and/or the e-book? It's just a pdf which can be accessed and downloaded from sappling. the access code was mailed to me but some people rec...

Moura Girgis 1F

Alara Aygen 3K wrote:I sometimes have the same problem. Putting the numbers that have powers in parentheses solves the problem.

I agree, you should make sure you add those paranthesis especially on exams because the slightest miscalculation can cost you the entire question

Moura Girgis 1F

that's right! all you need to do it download it through the link on ccle and it will automatically launch on your device

Moura Girgis 1F

snow and ice also undergo sublimation under certain conditions

Moura Girgis 1F

It should be up to week three, which is about thermochemistry!

Moura Girgis 1F

Scratch paper is definitely allowed for this quarter as well!

Moura Girgis 1F

Massimo_Capozza_1G wrote:Does anyone else have a problem when logging into Chemistry Community where you have to re-register each time you sign-in?

That should not be the case, perhaps you should try saving your username and password on your device so that you can automatically be logged in when you open the site.

Moura Girgis 1F

The K equilibrium constant can only change through a change in temperature, a change in concentration will not change the value of K.

Moura Girgis 1F

Although they are not the same, they are related. If you have not waited long enough for the reaction to reach equilibrium, you can't use K and, thus, must use Q to determine the reaction quotient.

Moura Girgis 1F

I mostly use PV=nRT in equilibrium to convert gases to concentration and vice versa, depending on the information given in the question. The equation is also helpful for Le Chatelier's Principle because you can see how pressure and volume are related to see volume changes would affect the reaction....

Moura Girgis 1F

That's right, since exothermic reactions will be losing heat, that means that the delta h must be negative.

Moura Girgis 1F

These are only optional and recommended to fill out, but it won't hurt you if you don't do them!

Moura Girgis 1F

Madison Wong 3H wrote:the first midterm is january 29 during your lecture time, but it's still 50 minutes. Before it was discussions, but now everyone takes it on the same day during their lecture time.

I didn't know that, thanks for the info! :)

Moura Girgis 1F

Did you hear oxygen went on a date with potassium?
It went OK.

Moura Girgis 1F

I like to play jazz music while im studying in order to get rid of any distractions in the house.

Moura Girgis 1F

Say if I made up the 5 posts that were due last Sunday for week one.. would I get full credit or be docked down for being late? My ta last quarter said I would not be able to get the points for that week since I had done them the week after they were due, but I ended up getting full points so maybe...

Moura Girgis 1F

I wouldn't be surprised if not too many questions from homework are on the final, so I suggest focusing more on the type of problems as opposed to specific ones from the textbook.

Moura Girgis 1F

I also agree! Organic Chemistry Tutor on YouTube as helped me solidify whatever Dr. Lavelle taught us in his lectures.

Moura Girgis 1F

Since you could see posts dating back from last year, I believe they should remain on the site as long as it is still functioning.

Moura Girgis 1F

Those are just one of the extra resources Dr. Lavelle has given us as practice for the midterms/final.

Moura Girgis 1F

we can't really go out, so I plan to spend as much time with my family as possible!

Moura Girgis 1F

Just finished my last final, FINALLY I can enjoy break!

Moura Girgis 1F

grades should be out by Saturday hopefully!

Moura Girgis 1F

Both bent and angular are the same, so you'd choose whichever one is given in the answer choices if it was a multiple choice format.

Moura Girgis 1F

wavelength should always be m unless the question is asking for a different unit.

Moura Girgis 1F

Thank you Dr. Lavelle! Looking forward to chem 14B!

Moura Girgis 1F

I like to listen to jazz music while I study, as it calms me down when I start freaking out over not understanding a certain concept.

Moura Girgis 1F

https://www.google.com/url?sa=i&url=https%3A%2F%2Fmccord.cm.utexas.edu%2Fchembook%2Fpage-nonav.php%3Fchnum%3D1%26sect%3D12&psig=AOvVaw1aUqGpVI60plDDL7M-zqye&ust=1608168782649000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCKirzNyt0e0CFQAAAAAdAAAAABAD Here is a link to a good illust...

Moura Girgis 1F

Jessica Hu 3L wrote:Then to clarify, a ring is what is a chelate? and that forms when it's a ligand-spare atom-spare atom-same ligand?

I am also confused on this. Could someone clarify?

Moura Girgis 1F

According to what Dr. Lavelle had mentioned in his previous lecture, a chelate is a complex containing a ligand that forms a ring of atoms, which include central metal atoms. Chelating ligands often bind cations tightly, because they are forming more than one bond.

Moura Girgis 1F

Thank you so much for this! It'll be very helpful for when I study!

Moura Girgis 1F

A slightly smaller or larger bond angle, in this case 109.5 degrees, could be the result of lone paired electrons which take up more space than the usual bonds.

Moura Girgis 1F

Since the final is cumulative, it might help to review any previous lecture notes from this quarter or watch the lectures themselves.

Moura Girgis 1F

How can we identify if a molecule is amphoteric or not? Other than water being a common one? Dr. Lavelle had characterized amphoteric compounds as having both basic and acidic character, so in the presence of a base, this molecule would act as an acid, and in the presence of an acid, it would act a...

Moura Girgis 1F

Since hydrogen bonding occurs through an intramolecular force, it would be considered a type of dipole-dipole interaction as opposed to a coordinate covalent bond.

Moura Girgis 1F

MichaelMendozaD1F wrote:is most "stable" the same as most likely or favorable? I believe they are synonymous in these types of problems but I just want to make sure.

yes, more stable lewis structures also tend to be those with the lower formal charge, so they are more favorable .

Moura Girgis 1F

Think of pi bonds as a vertical overlapping of bonds, so they cannot rotate, while sigma bonds consist of horizontal overlapping, in which they can rotate.

Moura Girgis 1F

I think that, in general, since both single and double bonds have a a sigma, but only double bonds have a pi, they could be referred to has simply pi bonds.

Moura Girgis 1F

I'm pretty sure that since Dr. Lavelle is increasing his sections, there should be a lot more openings, which means that waitlisted students should be able to get in without a problem.

Moura Girgis 1F

Alison Perkins 2C wrote:
jasmineculilap_2J wrote:You need 5 posts per week, so 35 posts are needed.

Do general questions and jokes count? Or strictly chemistry material?

Pretty sure that everything/anything posted counts!

Moura Girgis 1F

This equation basically refers to electron density and the likelihood of finding an electron within it.

Moura Girgis 1F

SamayaJoshi1A wrote:Hi! I don't think this is a necessary step for any of the questions. Dr. Lavelle just does this to show that there is a ratio and that the percentages should add up to 100 percent.

I agree, Dr. Lavelle just tries to show us the w=actual process, but it is not necessary.

Moura Girgis 1F

Although they should not have much of an effect on your answer, I would put it just in case :)

Moura Girgis 1F

Q: What is the chemical formula for "coffee"?
A: CoFe2
Q: What is the chemical formula for "banana"?
A: BaNa2

Moura Girgis 1F

All you have to do is go to "Quick Links" and then "Your Posts" !

Moura Girgis 1F

Those two are pretty interchangeable, they just require different units I think.

Moura Girgis 1F

Hi! I agree with the post above, and if I recall correctly, the horizontal trend is a bit stronger than the vertical. However, I'm unsure if there are any straight up exceptions to the atomic radius trend. I think Dr. Lavelle might have mentioned these exceptions in his pervious lectures where he d...

Moura Girgis 1F

Maybe you could try downloading the the answer key and then opening it from there? That's what I did so now the answer key is saved on my computer and I can access it anytime I want.

Moura Girgis 1F

I always eat a good, healthy, meal the day before my test and something light light a nutrition bar the morning of. That usually keeps me energized helps me think better when taking the test.

Moura Girgis 1F

This is so helpful, thank you!! Also, I think Chem_mod might be Dr. Lavelle only, not too sure though.

Moura Girgis 1F

I see that everyone is making bad chemistry jokes because all the good ones Argon.

Q: What did the scientist say when he found 2 isotopes of helium?
A: HeHe

Moura Girgis 1F

We can count the number of elements within an atom based on its atomic number, which is also the number of protons in that element. In an ion, it would be the atomic number plus the charge (negative or positive).

Moura Girgis 1F

Electronegativity trend is ultimately very similar to the ionization energy trend, as it increases in the periodic table from left to right and decreases down the periodic table.

Moura Girgis 1F

In regards to a Lewis structure, a long pair consists of valence electrons of one atoms which are neither bonded nor shared with any other atom.

Moura Girgis 1F

As Dr. Lavelle had mentioned in one of his previous lectures, these elements would be exceptions to the octet rule, which is why they could hold that extra electron.

Moura Girgis 1F

All you have to do is click on "Quick links" on the top left, then go to "your posts." You can filter it so that you check what posts you made within a select time frame.

Moura Girgis 1F

That symbol stands for "proportional to" and is used to describe how one thing is the same as or equal to another thing. Similarly, it can be used to describe something as "inversely proportional" to another thing when that second term has a "^-1" on it.

Moura Girgis 1F

When solving a problem, wavelength must always be written in terms of m, since the other variables in the equation would be in m. However, when writing the wavelength as the final answer, it should be converted to nm in order to determine the spectrum.

Moura Girgis 1F

The the several practice problems we have done for this class so far, the value for the Rydberg constant was 3.289x10^15, so that should be the only value you use when solving the problems as far as Chem14A goes.

Moura Girgis 1F

Yes! At least so far in Chem14A c is always a constant which represents the speed of light, so it should not change.

Moura Girgis 1F

The midterm was about 12 problems, with 50 minutes given for us to complete it. We could use the constants and equations handout as well as the periodic table handout as long as we printed it out and did not write anything on it.

Moura Girgis 1F

Since kinetic energy would be 0 in this scenario, you would just have to divide the total energy by the work function, taking into account whatever is already given to you or whatever you have previously solved in the problem.

Moura Girgis 1F

The units for wavelength is in meters, and the units for frequency is in Hz, or s^-1. Since the midterm is multiple choice, the only thing you should worry about in terms of units is being able to convert if it is given in any other unit, such as nanometers instead of meters.

Moura Girgis 1F

Just like in mg, the m stand for milligrams, the m in mol stands for milligrams. It is simply the prefix "milli."

Moura Girgis 1F

So when asking us to write an equation with an element that happens to be diatomic, like oxygen, would we always but a subscript of 2 with it? Because I feel like I have seen instances where there wasn't any subscripts with it.

Moura Girgis 1F

AustinMcBrideDisc3C wrote:
diegomartinez1F wrote:Mass of electron is given:

Me= 9.10938 x 10^-31 kg

Do we need to convert this to grams or can we keep it as kg?

We need to keep it in kg, as all of the other units include kg, such as Joules (kg.m^2/s^2)

Moura Girgis 1F

It is much easier to work with whole number in balanced stoichiometric equations, so that is recommended, although fractions in a balanced equation would not technically be wrong, just harder to work out. Dr. Lavelle also mentioned it would be better to use whole numbers when balancing stoichiometri...

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