CHEMISTRY COMMUNITY

Cavalli_1H

anode is on the left and cathode is on the right. if youre looking at the reactions taking place in in the cell, the anode is where oxidation takes place and the cathode is where reduction takes place

Cavalli_1H

raise e to the power of both sides

Cavalli_1H

it represents the equilibrium constant for water

Cavalli_1H

i think you'll need to match the units to the rydberg value you plug in

Cavalli_1H

its only necessary in deriving certain equations, but if theres no hw questions on it im sure we wont be asked a question that requires it

Cavalli_1H

you would generally look for the reduction/ oxidation of the atom which is why we look more closely at half reactions

Cavalli_1H

for part c, can someone explain how we get the units to be L^4 / mol^4 * s ? based on my setup, some of the Ls and mols should cancel so i'm a little confused

Cavalli_1H

it is essentially the difference in moles between to sides of a reaction or the net transfer of moles

Cavalli_1H

yes they will be provided but you'll need to know which is which and ways you can manipulate them to solve for its components and such

Cavalli_1H

you add an inert solid usually if the reactants and products of a half reaction within a cell are of the same species or if it contains a gas

Cavalli_1H

based on the correlation that K = [products] / [reactants] , if k> 1 then [products] > [reactants]. if if k< 1 then [products] < [reactants]

Cavalli_1H

K is a relative ratio so from my understanding it has no specific units

Cavalli_1H

for redox reactions you add them as needed on either side. depending on your method (there are several ways to do it), you'll most likely add OH- to sides that have an uneven charge or amount of O or H

Cavalli_1H

im not entirely sure but my ta instructed for us to just worry about using lines for this class at least

Cavalli_1H

Iona Pay wrote:Molecularity refers to the number of molecules that come together to react in an elementary reaction, and is equal to the sum of the coefficients of this elementary reaction. So, if you're talking about an elementary reaction, yes!

might seem silly but what do you mean by elementary reaction?

Cavalli_1H

a rate is denoted as a change in concentration over units of time. so M/s or mol/L^-1 x s^-1 would be the proper units

Cavalli_1H

the anode of the system is where oxidation occurs and the cathode is where reduction occurs

Cavalli_1H

charleejohnson1L wrote:this has always confused me as well, thank you for asking and thank you to those who answered!
is k the ratio of product concentration to reactant concentration at equilibrium?

yes, and because it is a ratio it does not have units

Cavalli_1H

It basically maintains electrical neutrality which keeps the cell from running its reaction to equilibrium too rapidly

Cavalli_1H

reviewing notes after lecture and trying to process them helps me to retain information. i also find that, as difficult as it can be sometimes to do practice problems without cross referencing solutions, that is definitely a good way to train your mind on the content. hope this helps :)

Cavalli_1H

yes, for galvanic cells, which have to be spontaneous in order for it to run, E has to be positive

Cavalli_1H

oxidizing agents are reduced by gaining electrons and reducing agents are oxidized by losing electrons

Cavalli_1H

my TA said that generally they most likely wouldn't ask a question about cell diagrams on a test because the method in the textbook is inconsistent and we don't really cover a concrete method of approach in lecture. he did say though as a general way of doing it, you should order the diagram as: ano...

Cavalli_1H

It basically maintains electrical neutrality which keeps the cell from running its reaction to equilibrium too rapidly

Cavalli_1H

I know that we're supposed to exclude solids and liquids and H2O when solving for K, but what if the H2O is denoted as a gas? do we include it in our K calculation?

Cavalli_1H

in my notes from lecture (week 2 friday) there is this problem: What is the pH of a solution with 0.100 M nitrous acid, HNO2(aq) and 0.150 M potassium nitrate, KNO2 (aq)? It is given that Ka=4.3x10^-4 for nitrous acid. The work that I have copied down excludes the potassium entirely, with the formul...

Cavalli_1H

q=mCdeltaT is used when youre given the mass of a substance, q=nCdeltaT is used when youre given the amount of substance in moles. if theres only one mole of a given substance you can assume q=CdeltaT

Cavalli_1H

the K of a reverse reaction is the inverse of the forward reaction

Cavalli_1H

enthalpy is a form of heat but heat is not a form of enthalpy

Cavalli_1H

hess's law can also be applicable to gibbs free energy for the reason of it being a state property

Cavalli_1H

i think when comparing structures before and after, its easiest to use colors and determine which bonds changed by either being added or formed. you should ask yourself, which bonds were there before but aren't there now? or which bonds look different?

Cavalli_1H

Wouldn't using -P mean the system lost energy? Lavelle said this in lecture today but the solutions manual says that the system has work done on it. okay, after looking more closely at the solutions manual, it says that you should calculate the change in V first, which is negative because of compre...

Cavalli_1H

Wouldn't using -P mean the system lost energy? Lavelle said this in lecture today but the solutions manual says that the system has work done on it. Yes! I thought it should be positive too because the question said there is compression, and today Lavelle said expansion should be negative. What am ...

Cavalli_1H

temperature is an important factor is how a reaction proceeds. Adding temperature increases the rate of production of products and therefore the K will shift.

Cavalli_1H

Partial pressures denotes the pressures of each gas in a larger mixture of gases the total pressure represents the sum of partial pressures.

Cavalli_1H

to start, you should count the number of valence electrons for each atom, and make sure not to forget to add or subtract charges it the molecule has +1 or -1 etc charges. from there you need to make sure each atom involved satiates the octet rule. you use a single dash to represent single bonds, two...

Cavalli_1H

He defined it as a property determined by current state, and is not dependent on path taken to obtain that state. He also used a graphical visual to show this, showing how even though two graphs end up at the same point, they both take different paths to get to whatever state they end up at. This ti...

Cavalli_1H

in the textbook's table 5G.2, theres two columns: K and Kc. I was under the impression that these two notations signified the same thing, however the values between the two differ on the table. can someone explain what the difference is and which column I should reference?

Cavalli_1H

When a change in partial pressure is applied on a system at equilibrium, the system shifts the position of equilibrium so as to minimize the effect of that change. So if volume decreases and there are more moles of gas on the left, then the reaction will shift right to accommodate the change, and if...

Cavalli_1H

stronger acids have weaker bonds. a strong acid is characterized by how it completely or almost completely dissociates in water. so in order for this to be the case, it makes sense then that acids have weaker bonds.

Cavalli_1H

it means you can only approximate a value for x on an ice table. you can sidestep the quadratic equation when you apply the approximation threshold. you do this because the value is so insignificant that it doesn't necessarily affect the solution

Cavalli_1H

concentration only affects K when you are working with Kc (involving aqueous solutions)

Cavalli_1H

it essentially means that when you have a stronger acid, you'll have a weaker conjugate base, and when you have a stronger base, you'll have a weaker conjugate acid

Cavalli_1H

the equilibrium constant will not change

Cavalli_1H

Kc denotes concentrations (aqueous solutions) and Kp denotes partial pressure (gas). when solving for Kc, make sure you do your work using brackets to specify the concentrations, and use parentheses for Kp to specify your partial pressures.

Cavalli_1H

they have opposite charges and therefore attract each other, unlike an electron/electron interaction where they repel each other

Cavalli_1H

I'm confused as to why Le Chatelier's principle really matters in predicting which way the equilibrium will shift. Why does this tell us about the reaction and its components? Because Le Chatelier's holds that a system in equilibrium will adjust as to minimize the effects of changes in something su...

Cavalli_1H

Q is calculated the same way as K, and K includes gases and aqueous solutions for its calculation

Cavalli_1H

can someone clarify what exactly a stoichiometric point is and how it helps to determine pH?

Cavalli_1H

yes, I think you just give it directly starting at p

Cavalli_1H

whether or not they make a solution acidic, basic or neutral

Cavalli_1H

yes, it is bent because there is one lone pair, meaning that there will still be repulsion to give it a bent shape. knowing that SO2 has 3 regions of e- density, with 2 of them bonding pairs and 1 lone pair, the VSEPR would be AX2E

Cavalli_1H

Since the structure of this molecule is tetrahedral, it is not the same that it looks when drawn as a 2 d Lewis structure. Essentially a tetrahedral structure can be rotated in different ways that is not accurately depicted in a 2 d structure, so if the H's and Cl's were opposite each other the mol...

Cavalli_1H

at the study session last night he said that dichloromethane (CCl2H2) is polar no matter where the Cls are arranged. Can someone explain why this molecule would still be polar?

Cavalli_1H

"Identify the salt that is produced from the acid-base neutralization reaction between (a) potassium hydroxide and acetic acid (b),(c) etc..."

What is a good way to approach this? I know that one product would have to be H2O, but other than that I'm not really sure where to go from there.

Cavalli_1H

the problem gives the name of a reactant (i.e. zinc nitrite) and asks for the acid and base that neutralize to form it. we won't be needing to know the nomenclature needed to solve this problem for the final right? I'm just looking up the molecular formula to solve the problem.

Cavalli_1H

when an acid or a base reacts with H2O, how can we determine based on the products that a certain reaction is relatively protonated or deprotonated? for example, how might the reactants of a reaction between a strong acid and water differ from the reactants of a reaction between a weak acid and H2O?

Cavalli_1H

practicing under similar conditions to the test really is the best thing to do. practicing under time constraint, without distractions, without solutions to peek at are all ways to nail the mental preparedness necessary to do well on these kinds of tests. its one thing to be confident in the materia...

Cavalli_1H

yes, this is what characterizes a Lewis base

Cavalli_1H

I don't think so, carbon isn't included in the list of exceptions to octet rule

Cavalli_1H

I think for both, but you'd only really need them for weak reactions

Cavalli_1H

also, I'm confused because there are some instances where you might have a certain molecule that could be arranged so that the dipoles cancel or do not cancel. how do we know which arrangement is the right one? are dipoles affected by arrangement?

Cavalli_1H

bloodorangefield wrote:Often acids will contain either H or OH

acids have OH? I thought it was bases?

Cavalli_1H

He might also do some review that Friday before finals kind of like how he did before the midterm with practice problems

Cavalli_1H

I'm sure that will work as long as its labelled!

Cavalli_1H

I was out of lecture Wednesday and Friday this week for personal reasons, and I was wondering if someone could share the general topics covered so I can do some of my own catching up.

Cavalli_1H

How do electron configurations and hund's rule come to play when figuring out hybridization?

Cavalli_1H

Does anyone know if material covered in today's (Monday) lecture will be covered on test 2?

Cavalli_1H

Also does anyone know if material covered in today's (Monday) lecture will be on the test as well?

Cavalli_1H

can someone explain the 'cis' and 'trans' that he used to describe polar and non polar molecules? what does this have to do with 'preferential interactions'?

Cavalli_1H

can someone explain why the seesaw shape is more favorable?

Cavalli_1H

I realize that there are certain times when molecules form trigonal pyramidal shape the bond angle is <109.5, but can someone explain why? What makes this way and how do we know that it will be <109.5?

Cavalli_1H

what exactly do regions of 'electron density' mean? I know it would have to include bonds but does it include lone pairs as well?

Cavalli_1H

didn't he say that a little bit of the end of the content from the midterm would be covered on the test as well?

Cavalli_1H

why is it that P, S and Cl can accommodate more than 8 valence e-? He explained it but his I'm still pretty confused why

Cavalli_1H

Do varying bond lengths (single vs. double bond) effect the overall share and behavior of a molecule?

Cavalli_1H

(theres a table provided) The first and second ionization energies of P, S and Cl are listed in the following table. Explain why the first ionization energies of P and S are nearly the same, whereas the second ionization energy of sulfur is much greater than than of P. This isn't on the list if prob...

Cavalli_1H

in the formal charge example we did in class, why is it again that he said the central sulfur should not have a charge, and that most central atoms don't have a charge?

Cavalli_1H

what does it mean when resonance structures are 'delocalized'? I keep hearing the word thrown around and I just need some clarification on what it means.

Cavalli_1H

I know that the stern and Gerlach experiment concluded the spin of certain electrons, but does anyone know how and why?

Cavalli_1H

they are both guidelines that help to figure out electron configurations. you use both to obtain ground state e- configuration

Cavalli_1H

what were the electron configuration exceptions, and does anyone know why they are exceptions? additionally, other than asking what the exceptions are on an exam, what kind of questions would test this knowledge of exceptions?

Cavalli_1H

can someone explain how/why we know that electrons have wavelike properties? I know he related wave properties to electrons but I couldn't understand the conclusion that electrons have wavelike properties based on diffraction patterns and such

Cavalli_1H

constructive interference is when the maxima of two waves add together and the waves are in phase w each other and destructive interference is when the waves are out of phase and cancel each other out rather than adding together.

Cavalli_1H

this question is asking you to consider some conceptual ideas. for (a), energy of the electron increases, as energy is a function of n. for (b) we know n will increase because the electron is transitioning from n=1 level to n=2 level. for (c) l increases because the electron is going from l=0 for s ...

Cavalli_1H

in lecture Lavelle talked about the relationship between the intensity of light and frequency/wavelength of light. can someone explain this correlation? also, how do we gauge intensity of light?

Cavalli_1H

I think to check your grades you go to myUCLA and look under exam and homework grades

Cavalli_1H

also does anyone know if partial credit will be given? like either just for showing some kind of work or having rounding/sig fig errors

Cavalli_1H

with the water example, I think he meant that, at a certain point in shrinking the stream of water, you'd get to a point where the smallest amount (a single H20 molecule) could be able to pass through, and when this happens there'd be 'jumps' of water pouring out, and not a constant stream. the clas...

Cavalli_1H

im not sure exactly which ones we need to know but I do know that the text book has a section on nomenclature on page F29 if you want to study those :)

Cavalli_1H

I think its best to be as accurate as possible throughout the problem and then give your answer in sig figs at the end

Cavalli_1H

if the problem doesn't specify what the chemical formula I think for now you can probably just look it up. I think we might get to what each name means if you're not sure yet

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