CHEMISTRY COMMUNITY

Julia Todorov 2F

Thanks Dr. Lavelle for always starting lecture with the music and fun intro, it always gave me something to look forward to compared to all other lectures and you made chemistry fun!

Julia Todorov 2F

yes it is possible! it takes very high concentration of H+ but it is possible

Julia Todorov 2F

normally Kelvin because that is the SI unit, but sometimes if you use celsius the units will cancel out but I would play it safe and just use kelvins

Julia Todorov 2F

if gibbs free energy is negative, then it is spontaneous or favorable and when it is positive it not spontaneous and unfavorable

Julia Todorov 2F

what are some content reminders/ key concepts you think are important to remember for the final?

Julia Todorov 2F

diddy reese is a westwood classic!! also the theater is really cool thats where they did the spiderman premier

Julia Todorov 2F

if the standard reduction potential is positive then it is spontaneous

Julia Todorov 2F

my best study spot is the rooms in Boelter. me and my friends will go into whatever is empty and use the white board to write out problems and work at the desks

Julia Todorov 2F

a catalyst impacts a reaction by changing its pathway and lowering the amount of activation energy needed which in turn speeds up the rate of the reaction!

Julia Todorov 2F

F is faraday's constant which is 96485 C/mol

Julia Todorov 2F

no the slow step can vary

Julia Todorov 2F

I think the best way to study for conceptual questions is reading through the textbook because it goes into depth on all the concepts and how everything works. taking notes on the textbook and comparing it to lecture notes helps me piece everything together and understand the concepts better. watchi...

Julia Todorov 2F

yes thats correct! if the system has negative work it is losing energy by doing work on something else

Julia Todorov 2F

gibbs free energy is the amount of energy available to do work, if negative the system is spontaneous and does not need energy for the reaction

Julia Todorov 2F

they are not the same, free energy is the amount of energy available for work while activation energy is the amount of energy needed for a reaction to occur/ for reactants to become products

Julia Todorov 2F

an enzyme is one type of catalyst meaning they both speed up the rate of a reaction by lowering the action energy needed and shortening the path of the reaction

Julia Todorov 2F

k' s the rate for the reverse reaction while k is the rate for the forward reaction. when you have both you can use them to find K/ the equilibrium constant by doing k/k'

Julia Todorov 2F

Pt goes on the outer most part of whatever side it is on, so it would go left most if on the anode and rightmost if on the cathode

Julia Todorov 2F

unimolecular reactions have only one reactant while bimolecular reactions are the collision of 2 species

Julia Todorov 2F

overall it depends on the slowest steps, so the other speeds of the steps won't necessarily be significant in determining the rate of the reaction

Julia Todorov 2F

the kinetics determine the rate of the forward and reverse reactions while the thermodynamics determine the favorability or spontaneity of the forward and reverse reactions

Julia Todorov 2F

I do not think those exist because the whole purpose of a catalyst is to speed up the reaction and lower the activation energy. If it does not do that I dont think it would be considered a catalyst

Julia Todorov 2F

I would assume its the same link that you used to use for discussions, but just email your TA and ask for the link to be sure

Julia Todorov 2F

personally I cannot listen to music when doing intense studying I focus too much on the music

Julia Todorov 2F

intermediates are produced and then used up in a reaction, while the catalysts are not consumed in the reaction. so if during the steps a compound is cancelled out, it is an intermediate but the catalyst has to be there in the beginning

Julia Todorov 2F

intermediates are things that are created then used up within the elementary steps of a reaction, they show how we got from the initial reactants to the final products

Julia Todorov 2F

cooling slows a reaction because the molecules aren't moving as quickly at low temps. he mentioned a fridge when talking about this and I think it really helps to think of it with food, it will go bad/mold slower if kept in a fridge because those cool temperatures slows that reaction

Julia Todorov 2F

adsorption is when molecules stick the surface of a solid rather than flowing in which is absorption

Julia Todorov 2F

Can someone please explain how to find the steps when given an reaction? How do we know which one is fast and which one is slow?

Julia Todorov 2F

it means that an inc/dec in concentrations does not affect the rate of the reaction, these are pretty rare

Julia Todorov 2F

TS is the transition state and is the max energy or "top of the hill"

Julia Todorov 2F

first order reactions are the most common, zero order reactions are pretty rare

Julia Todorov 2F

honestly I prefer online because I like being able to pause the lectures/ rewind if I need to so I feel like it helps me learn better, but it really is a personal preference so you should try both

Julia Todorov 2F

the slope would be -k

Julia Todorov 2F

seconds is the SI unit but you can use any unit as long as it stays consistent

Julia Todorov 2F

we need to balance the equations so that the number of electrons is equal in both of the half reactions. so if one half reaction has 2e and the other has 4e, we would have to mutiply through the first one by a coefficent by 2 so that they both would have 4e and can be cancelled when writing out the ...

Julia Todorov 2F

yes we assume it is 1 unless it tells us otherwise

Julia Todorov 2F

spontaneous simply means that it is thermodynamically favored but it does not say how fast. kinetics is more of the rate/speed of the reaction

Julia Todorov 2F

yes youre correct!

Julia Todorov 2F

he just wants us to not only be asking questions, but answering them as well. so 2/5 posts have to be answers to other students questions for week 9 and 10

Julia Todorov 2F

Its going pretty good I like the math side of 14B better than 14A but it is definitely harder than 14A

Julia Todorov 2F

K is the equilibrium constant, so it only refers to when the reaction is at equilibrium. Q is calculated the same way with the ratio of products and reactants but any point of the reaction and can be used to determine if the reaction at that point is at equilibrium, favoring the reactants, or favori...

Julia Todorov 2F

the one being oxidized is the anode and the one being reduced is the cathode. the electrons are flowing into the cathode from the anode and usually the anode is drawn on the left

Julia Todorov 2F

doing the textbook problems and going to step ups/ workshops is what helps me study the most. flashcards are also super helpful and I would really recommend going to the final reviews to help prepare for the final!

Julia Todorov 2F

the equation is t(1/2) = 1/(k*[a]0)

Julia Todorov 2F

F is Faraday's constant or 96485 coulomb per mol

Julia Todorov 2F

you have to look at the units to know which R to use, but from what I've noticed most of the times when you are using it in PV=nRT then its the .082 R and then the integral equations usually use the 8.314 one

Julia Todorov 2F

yes the final is cumulative and the topics we spend the most time is are the topics that will more heavily be tested

Julia Todorov 2F

oxygen usually does have an oxidation number of -2, there are some other cases like H2O2 where O has an oxidation number of -1! in peroxides it has -1 oxidation

Julia Todorov 2F

if we forgot to launch the browser before but still get the question right does that mean we will not recieve the 8 points?

Julia Todorov 2F

the product of [OH-] and [H+] are 10^-14, so you can divide 10^-14 by [OH-] to find [H+] and vice versa

Julia Todorov 2F

they go in alphabetical order so the chloro would go before the oxalato, any prefix on chloro/ any other ligand is ignored for the order they are written in

Julia Todorov 2F

to get from pH to [H+] you do 10^-pH value! and for pOH you would do 10^-OH

Julia Todorov 2F

Hi can someone please explain to me how I would figure out this problem from the pH section of the textbook?
The molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?

Julia Todorov 2F

tbh I'm pretty stressed. happy dead week I pray we all make it out alive

Julia Todorov 2F

I would recommend reading the textbooks for sections you dont fully understand, and working through the problems too. go through the outlines and make sure you understand everything there and I would focus on quantum becuase thats what we spent the most time on.

Julia Todorov 2F

tetrahedral and square planar!

Julia Todorov 2F

I would focus on quantum because we spent the most time on it, but honestly everything is necessary to know

Julia Todorov 2F

Thank you these are super helpful :)

Julia Todorov 2F

single bonds are just sigma bonds, double bonds have one sigma and one pi bond, and triple bonds have one sigma and two pi bonds

Julia Todorov 2F

a radical is when an atom has an unpaired, or odd number, of electrons!

Julia Todorov 2F

I think the easiest way to figure out hybridizaton is to count the number of bonded atoms and lone pairs, or just the regions of electron density. then that number should match the subscripts of s p and d, remembering s has one orbital, p a max of 3, and d a max of 5. so if there is 5 regions of ele...

Julia Todorov 2F

everything we learn in this class will be on the final, including week 10 information

Julia Todorov 2F

we have no lecture on wednesday or friday, just tomorrow!

Julia Todorov 2F

that is representative of the greater than sign, so the last item on that list is the smallest and first is largest

Julia Todorov 2F

that is representative of the greater than sign, so the last item on that list is the smallest and first is largest

Julia Todorov 2F

yes the final covers all of the quarter materials

Julia Todorov 2F

seesaw is slightly less than 90 degress between axial and equitorial and slightly less than 120 degrees between equitorial atoms

Julia Todorov 2F

either watch criminal minds or take a nap

Julia Todorov 2F

going to workshops, step ups, re reading textbook sections/ rewatching lectures about material you weren't 100% about, and redoing some textbook problems from each section are all great ways to prepare

Julia Todorov 2F

your formal charges do not seem to be right, try recalcuating them. the oxygen that is single bonded should have a formal charge of -1 because 6 - (6 + 2/2) = -1 (valence - (unpaired electrons + bonded/2))

Julia Todorov 2F

when you draw out the lewis structure it may look like the dipole moments cancel out, but if you think about it in the molecular 3d shape it is, then it might be easier to picture how they actually do not end up cancelling out. the shape is not symmetrical so they do not cancel

Julia Todorov 2F

the stronger the intermolecular forces, the higher the boiling point. for example if you had two non polar molecules with only london dispersion forces, the one with more molar mass (or just bigger) would have the stronger london dispersion force, and in turn a higher boiling point

Julia Todorov 2F

the boiling point is determined by your intermolecular forces, so the stronger the forces, the higher the boiling point. this is the forces like hydrogen bonding, dipole- dipole, and London dispersion forces

Julia Todorov 2F

axial is the vertical plane, I like to think of it as the atoms above or below the central atom, while equitorial is the horizontal plane or the atoms to the left/right and in front/ behind of the central

Julia Todorov 2F

for these I would draw out the Lewis structures and see if the dipole moments cancel out. NH3 and BrF3 are both polar because the lone pairs change the geometry and push down the bonded pairs, so the dipole moments aren't the same in opposite directions. CO2 is non polar since there are no lone pair...

Julia Todorov 2F

Reading the textbook helps a lot. Sometimes I will try the textbook problems without reading the textbook first to see what I already know, then I read through and it really solidifies what you already know and helps clarify the things you didn't. Sometimes though, the textbook will go into detail a...

Julia Todorov 2F

the grades are currently up in ccle!! HAPPY THANKSGIVING EVERYONE I'm thankful for this awesome school we go to

Julia Todorov 2F

this right here taught me better than any study tactic ever could

Julia Todorov 2F

A is the central atom, X is the number of bonded pairs (remember even if there is a double or triple bond it still counts as one single region of electron density) and E is the number of lone pairs

Julia Todorov 2F

Most TA's will most likely just check to make sure you have 50 total posts by the end of the quarter, but it is recommended to do 5 a week. Ask your TA to clarify and see if they are checking your amount of posts weekly

Julia Todorov 2F

Q: Anyone know any jokes about sodium?
A: Na

its okay I didn't laugh either

Julia Todorov 2F

I think it is important to keep them in the back of your mind because they do seem to come up every now and then, and I can imagine that they will continue to as the our chem careers continue. But, based on the midterm it seems like most compounds will be given so I feel like complete memorization i...

Julia Todorov 2F

The element with the lowest ionization energy should be placed in the middle of the lewis dot structure which you can figure out looking at the periodic table. it inscreases from left to right, and decreases moving down

Julia Todorov 2F

I don't think we have to know how to calculate it the numbers he was giving us were from experiments. But it is important to know that double bonds are relatively shorter than single bonds!

Julia Todorov 2F

Yes! Francium would have the largest and helium the smallest!

Julia Todorov 2F

After the midterm I realized I was way more familiar with calculations and using equations than I was with the conceptial questions. Does anyone have any tips/ suggestions for how to better study and understand these concepts for future exams?

Julia Todorov 2F

the conversion factor for eV is 1eV = 1.602*10^-19 J, which can be found on the constants and equations sheet! So if you want to convert jules to eV, you would divide the jules by 1.602*10^-19 J

Julia Todorov 2F

The Aufbau principle, or building up principle, states that the orbitals with lowest energy fill up first. This is why electron configurations won't be something like 1s1 2s2 2p3 3s2 in the ground state. The electrons want to fill the shells in order from lowest to highest energy

Julia Todorov 2F

This is the most stable because the closer each atom's formal charge is to zero the less energy it has. Sulfer is not like oxygen, nitrogen, carbon, and flourine in the sense that they must have 8 electrons no more no less since but sulfer can have more. Basically the closer an atoms formal charge i...

Julia Todorov 2F

No, percent composition does not have have to be a whole number. I think you may be confusing that with stoichiometry coeffections when balancing equations or when you're trying to solve for the empirical formula the moles of the elements also have to be whole numbers. For percent composition, thoug...

Julia Todorov 2F

A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0 mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transer into a flask to obtain a) 2.15 mmol Na+; b) 4.98 mmol CO3...

Julia Todorov 2F

I was working through the fundamental problems and am stuck on how to do part c of question E9 Epsom salt consists of magnesium sulfate heptahydrate. Write its formula. a) How many atoms of oxygen are in 5.15 g of Epsom salts? b) How many formula units of the compound are present in 5.15g? c) How ma...

Julia Todorov 2F

Breaking Bad is my all time favorite show. I can't rewatch TV shows but that one is such a masterpiece I had to rewatch. And the main character is a chemistry teacher so it'll guarantee you an A in the class :)

Julia Todorov 2F

The step up sessions are started up and are under the "Undergraduate Assistant (Peer Learning) Sessions and
Step-Up Program" form on his website. I've been to a few and they are already super helpful so far!! Definitely go to those and the workshops for extra practice and review

Julia Todorov 2F

I initially got the question wrong because of the order I put the atoms in and was so confused on how to get the right answer. Thank you for posting this discussion and thanks to the replies now I understand this was super helpful

Julia Todorov 2F

This post reminded me of a college essay I wrote during application season where a student wrote about how baking chocolate chip cookies got him so interested in chemistry. It was such an amazing essay and I'm pretty sure he ended up in Stanford or some crazy Ivy! I feel like we really tend to forge...

Julia Todorov 2F

I took regular chem my sophomore year of highschool and it honestly seems like I know close to nothing about chem! The step up zoom program he created has been really helpful so I would suggest going to some of those and the modules he posted helped a lot too. Youtube and Khan Academy are always goo...

Julia Todorov 2F

I always base my rounding off of the problem and how many sig figs it is using/ asking for. But a good tip is to not round until the very end of the problem and just use exact calculations throughout the entire problem to prevent a rounding error from happening.

Julia Todorov 2F

You do not need to balance it but you will need to use the 1:1 ratio you can see from the equation to help solve the problem!

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