CHEMISTRY COMMUNITY

alex_4l

I was struggling with this problem as well so thank you for the clarification!!

alex_4l

Could someone give an example of when the Arrhenius Equation would have to be used?

alex_4l

Are the answers to this still going to be posted?

alex_4l

You could be able to determine the order of a reaction or the order in respect to a certain reactant by experimental data. In this case you would see how the concentration changes in relation to the change in rate. Another way to find the order of the reaction is through the units of K, the rate co...

alex_4l

ideal gases obey gas laws, molecules take up no space and have no interactions!

alex_4l

I would suggest trying to memorize them and their meaning as much as you can, more comprehension about it is only going to help you!

alex_4l

I appreciate so much how much time and effort the UAs and TAs put into making sure we got the best out of our time with them. It's really easy to get a TA/UA that doesn't really care about the student's progress but I never felt that way about the ones I came in contact during the quarter. Their dri...

alex_4l

Dear Dr. Lavelle, I absolutely love whoever came up with this idea and all those who participated in it. I had you for 14A and although your class was a struggle for me (getting used to the quarter system and the academically challenging material of the classes here) I'm very grateful I was able to ...

alex_4l

Does anyone have any idea how turning the final in will work if its take home? Like is it going to be multiple choice or something like that

alex_4l

I would think that some step ups and review sessions would continue since they're under 100 people, but at the same time some of the TAs and UAs might leave. I think our professor would also keep his office hours to accommodate for that, but at the same time I'm not 100% sure. I'm sure he will addre...

alex_4l

He hasn't sent an email out yet but he should be telling us the plan asap!!

alex_4l

If your TA doesn't reach out I'd send pictures just in case and ask if there is still discussion!

alex_4l

205405339 wrote:From what I remember from Lavelle's lecture, catalysts are purely mechanisms that lower activation energy and are not included in the equation, therefore, they will not be in the rate law

That's what I remember from lecture as well!

alex_4l

The definition of a dimer is "is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular" hope that helps!

alex_4l

I doubt our professor would have the final in person but then again I have no idea, I would just keep paying attention to the material and studying and being alert for responses

alex_4l

I'm not sure if our discussion sections will be cancelled since those are less than 100 people but I would email your TA just in case

alex_4l

Thank you so much :')

alex_4l

They should be going on since the online action also doesn't start until tomorrow!

alex_4l

I would assume the lecture is going to be online unless our professor says differently tonight, hope that helps

alex_4l

I would just focus on the material and studying more than where or how it will be given. It's best to prepare for the content to be ready for whatever can happen

alex_4l

Thank you!

alex_4l

Personally what I do is I look "Your posts" tab at the date starting from January and go through each of my posts to make sure I'm accounting for times I've posted twice and I keep a paper in my notebook with each post title and how many I have in each one to make sure I'm counting accurat...

alex_4l

I wouldn't count on the homework problems that show up on the final to be word for word. It more than likely will be the format of how the problem is and will be reworded. As long as you understand the homework problems, go over the midterm and tests and have a clear outline of the notes you should ...

alex_4l

They are sending emails of the news in waves for if you haven't gotten it yet you will soon!

alex_4l

So Gene Block has spoken and initiated that all classes are online starting tomorrow. That being said if our professor chooses to still have class in person (is that against the law? not sure) that being said he would more than likely have to give an alternative option, such as having a link to his ...

alex_4l

Honestly since the news just broke out about online classes/finals there are a number of ways our professor could choose to continue with the course. I'm sure he will send out an email in a few hours. I personally would expect optional review sessions that will be recorded and either a take home fin...

alex_4l

Does anyone have an idea if it will be proctored?

alex_4l

G = 0 when the rate of forward reaction equals the rate of the reverse reaction (equilibrium)

alex_4l

Isothermal is when the temperature is constant even though heat and volume change very slowly so other properties can adjust (making it seem like temperature is constant). When heat is added, volume expands and the pressure changes. Isothermal shows that Delta U = Q - W = 0 because the internal ener...

alex_4l

alex_4l wrote:W is positive when work is done BY the system
W is negative when work is done ON the system

That being said, this is only for the equation of delta U = Q + W implying that it is a closed system with no other factors involved

alex_4l

W is positive when work is done BY the system
W is negative when work is done ON the system

alex_4l

An easy way to look at it is:

Q is positive when heat is transferred INTO a system (endothermic)
Q is negative when heat is transferred OUT of a system (exothermic)

alex_4l

When delta G is negative = it is spontaneous in the forward direction and non-spontaneous in the reverse direction When delta G is 0 = this is equilibrium so the reaction is reversible, this means that the rate of the forward reaction is equal to the rate of the reverse reaction When delta G is posi...

alex_4l

Most of the time they have one TA grade 1-2 problems for every test and rotate so the full test is graded by different people

alex_4l

8.314 J/mol·K is the most common used form for the R gas constant, but there are other types of numbers given for it depending on the units. I would suggest memorizing this number just in case the formula sheet has a different value on it since this is the most common used form of it used in our pro...

alex_4l

Also, this theory might not be 100% the truth of what is going on with matter while the universe is expanding because it's just an idea and cannot be proven from our knowledge and understanding until technology advances to a more extreme level. However, this is the most common and easiest to underst...

alex_4l

In regards to the question of matter having a sort of "limit," in astronomy it's explained that every source of matter is concentrated into different things and recycled over time (example: when we die our bodied and energy and released back into decomposition and when a super nova occurs ...

alex_4l

I'm not sure what exactly will answer your question, but-- Heat can be used in regards to the generality of heat transfer as a whole, what kind of reaction it is (endo or exo) and if the reaction needs heat in regards to something like a combustion Temperature is more of the temperature a reaction i...

alex_4l

In notes for lecture today, the professor explained that the way to change the energy of an open system was to add or remove the amount of substance in a system. For a closed system, you either heat or cool the system aka the piston compression and to do work on the system or let the system do work ...

alex_4l

Thank you for clarifying!

alex_4l

Exothermic is negative due to the fact that it is releasing energy and endothermic is positive due to the fact that it absorbs energy

alex_4l

I'm just a little confused but can someone tell me the difference between enthalpy and entropy in regards to when to use them?

alex_4l

Yes this is correct, positive is always endothermic, negative is always exothermic

alex_4l

Doing problems from acids and bases equilibria towards the end of the section where they get harder should be fine for this week!

alex_4l

They should give us the heat capacities on most of the problems, but it wouldn't hurt to memorize some of the basic elements or compounds like water

alex_4l

Leave out water, solids and other liquids but aqueous and gases can be used in the table

alex_4l

You can also search "Test 1 study guide" in chemistry community and can find problems!

alex_4l

Basically Q is referring to anything other than the equilibrium

alex_4l

An easy way to remember it is
T increase, shift left
T decrease, shift right

alex_4l

You shouldn't have to memorize any values for Ka and Kb, just understand how to work out the formula for each and that Kw=Ka x Kb and Kw=10^-14

alex_4l

The Law of Mass Action is the principle that the rate of a chemical reaction is proportional to the masses of the reacting substances. Relating that to chemical equilibrium, the Law states that "if the system is at equilibrium at a given temp, then the following ratio is a constant." It's ...

alex_4l

Do you want the answers to this or is there some particular part of the problem you don't understand?

alex_4l

Q and K are similar in the sense that they are calculated the same way with products divided by reactants. They are different however with K being the equilibrium constant and Q being the reaction quotient. Q happens at any time during the reaction and K is the overall equilibrium

alex_4l

Also to help with studying if you haven't taken a class with this professor yet, I would suggest doing all the homework problems to those sections, they help a lot!

alex_4l

My TA said the test would mainly be on the first two sections on the syllabus, "chemical equilibrium and acid/bases equilibria"

alex_4l

Thank you so much! That was actually really informative

alex_4l

The goal is always to make the charge of each atom in the Lewis Structure to be closest to 0, so the best resonance structure is when the atoms are closest to 0 but if that's not possible just try to get the central atom to 0

alex_4l

I hated that question it took me so long to remember it from lecture. Will that be more emphasized in 14B?

alex_4l

It's always helpful to memorize but I don't think it's necessary

alex_4l

Alexa Hernandez 3k wrote:See your grade on my UCLA, add the pints and then divide by 500 points...

That's what I've been doing and it's been really helpful

alex_4l

You can also look at the number of lone pairs on N,O or F atoms

alex_4l

In regards to bond strength, HCLO2 stronger because of the types of bonds in the lewis structure (ex: double, single) or because of the bond angles?

alex_4l

I've been watching youtube videos that pertain to specific topics I'm confused about. Sometimes it's tricky to find really good ones but I find it really helpful to see someone else explain specific topics I need review on since you can rewatch them. this is what helped me the most!! Kaplan videos ...

alex_4l

Cisplatin also does this by replacing something in the guanine molecule with a water molecule so that DNA synthesis cannot occur

alex_4l

Also an easy trick is just to count the number of electron density areas around an atom. 4 areas is sp^3, 3 areas is sp2, 2 is sp

alex_4l

I'm pretty sure the final will mostly be on new topics we've learned with some fewer questions about the other things we've already been tested on. I would focus studying on new topics and just refresh yourself on the old material

alex_4l

My TA discussed the different aspects of pH that I think would be useful to understand for the final
pH -log [H+]
pH -log[OH-]
Ka= acid dissociation constant
Kb= base dissociation constant
PKa= -logKa
Pkb= -logKb
Kw= Ka X Kb (H+ X OH-)
and that pH + pOH will always = 14

alex_4l

The steric number is the amount of atoms plus the number of long pairs bonded/attached to the central atom used in VSEPR to determine molecular geometry

alex_4l

I think you first calculate the pH using -log(10) of either [H+] or [OH-] and then determine if the acid or base is weak or strong. Closer to 7 would be a weak acid (since 1 is the strongest acid) and closer to 7 would be a weak base (since 10 is the strongest base)

alex_4l

Is our final on the 8th or 9th?

alex_4l

it's a form or chemotherapy to stop the growth of cancer cells, unfortunately it also impacts the healthy cells from multiplying. It usually impacts healthy cells that multiply quickly, such as hair and blood cells.

alex_4l

Bronstead acids is when the acid is a proton donor and a Lewis acid is an acid that accepts the electron pair

alex_4l

I think it's the homework problems in the molecular shape and structure section that involve hybridization (since we didn't have that on test 2) and the last 2 sections of homework problems on the syllabus

alex_4l

Does that mean that our discussions are cancelled this week?

alex_4l

Hybridization is basically the concept of mixing atomic orbitals into new hybrid orbitals (these can have new energies, shapes different from the component atomic orbitals) which then make it suitable for the pairing of electrons to form chemical bonds. The regions of electron density = the number o...

alex_4l

Does anyone what day the cutoff of lecture material will be?

alex_4l

I made a quizlet for the angles in relation to shapes and that has really helped me so far!

alex_4l

electron affinity, ionization energy and electronegativity all follow the same trend of increasing upward and to the right, the only one that's different is size/radius which is downwards and to the left

alex_4l

Khan academy videos are super helpful! I also go to the Step Up programs that are taught by the TAs as well as office hours which are really beneficial as well. I've also found that just reading through the posts on chemistry community provides a lot of insight on topics that I don't understand or n...

alex_4l

You mean like one of the exceptions of a bond with electron deficiency?

alex_4l

I'm pretty sure that it covers post-midterm information! But does anyone know if the final is cumulative or just topics after test 2?

alex_4l

You don't have to take 14B and 14BL together! I know plenty of people who are taking them different quarters apart. If you're deciding between either 14B/14BL or 14C/14BL I would say 14B/14BL since they're similar topics that would correspond with each other better than two different aspects of chem...

alex_4l

Adding on to this, if two elements are on opposite sides of one another on the periodic table, they most likely will be ionic due to the size as well since the bigger element would be dominating the bond over the smaller one

alex_4l

I understand the concept of the fluctuating dipole due to the spontaneity of the electrons and their movement. However, how would this impact the way that we write out an example of the dipole on a test or a homework problem? Would it stay the same and we just have to know the concept or would we ha...

alex_4l

Here's some rules for polarity and exceptions of when it's non-polar. Hope this helps! Everything can be considered a polar bond except for two instances 1) carbon and hydrogen bond (not polar mostly just equal sharing of electrons) 2) atom bonded to the identical atom (no difference in electronegat...

alex_4l

Could someone post an example of a coordinate covalent bond and a regular covalent bond?

alex_4l

On a test, will it specify that we need to calculate the formal charge or should we do it either way just to be sure?

alex_4l

Malia Shitabata 3H wrote:So the photons are acting as particles when emitted in the photoelectric effect, but I also wrote in my notes that electrons act as waves. Does it acts as both a wave and a particle or did I misunderstand the lecture?

They can behave as both given the circumstance

alex_4l

Also, if the Lewis Structure contains all the same elements then the molecule is nonpolar, but if there is just one difference it can be polar. For example, if there are 4 Cl attached to a centered Cl, that would have polar bonds but be a nonpolar molecule. But if there are 4 Cl attached to a center...

alex_4l

Follow up, there's 2 things to make sure you check when drawing a Lewis Structure in order to make sure it's correct 1) looking back at total of electrons count to make sure the total has been presented in the structure 2) each atom must have 8 electrons (doesn't matter about single or multiple bond...

alex_4l

Here's some general rules for drawing Lewis Structures! 1) Write the correct skeletal structure for the molecule -hydrogen atoms will always be terminal (outside) -many molecules tend to be symmetrical ***the least electronegative atoms is ALWAYS the central atom 2) calculate the total number of ele...

alex_4l

Going off of that, I know 4 specific chemical structures that have the octet rule (numbers 1/2 are electron deficient exceptions with less than 8 electrons and 3/4 have expanded octets with more than 8 electrons) 1) NO N has 5 electrons, O has 6 electrons which totals in 11 electrons. Usually every ...

alex_4l

I understand the equations and when to use them, I just don't understand why 10 was chosen as the value for V in the last equation and why it wasn't the number we had gotten for it in the earlier equation.

alex_4l

Would it be possible for someone to post a worked out example of converting something to angstrom? I just want to make sure I'm doing the conversion correctly, thank you! For example, if you wanted to convert 1.91 meters into Angstroms, you would do 1.91m*(10^-10 Angstroms/1m), which equals 1.91x10...

alex_4l

Amina Durrani 3G wrote:Wait, why can you only use a noble gas again? I’m little confused.

It's because those are the only elements on the periodic table that have a complete shell with no valence electrons on the end, so they are the core electron used!

alex_4l

This is a table I've used in the past that sort of explains subshell letters in correlation to electron shells, it's super simple but I hope this helps! Shell # of Subshells Letters Specifying Subshells n=4 4 s, p, d, f n=3 3 s, p , d n=2 2 s, p n=1 1 s

alex_4l

In class, we had a problem where wrote out the electron configuration for Calcium. Instead of doing the whole electron configuration, we wrote [Ar] 4s^2. A few people next to me were confused about this so I thought I'd explain why. This method is a sort of shortcut for writing out electron configur...

alex_4l

Would it be possible for someone to post a worked out example of converting something to angstrom? I just want to make sure I'm doing the conversion correctly, thank you!

alex_4l

In discussion 4C this past week, we did an equation and I was a little confused with one of the steps the question was "green color appears when visible light has a wavelength of 780nm, what will E=,V= and V-=?" for this problem we used E=hc/sigma to get 6.626x10^-34JS x 3x10^8m.s^-1/ 780x...

alex_4l

This equation also shows that energy is directly proportional to frequency! The equation E=hc/lambda shows that energy is indirectly proportional to wavelength.

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