CHEMISTRY COMMUNITY

KaleenaJezycki_1I

Why is this??

KaleenaJezycki_1I

Thank you so much for the continual support throughout the last two quarters!

KaleenaJezycki_1I

Test 2 grades are already on myucla.

KaleenaJezycki_1I

Rohit Ghosh 4F wrote:Yes, it does not really matter which one is T1 and which one is T2, as long as they're correctly matched with their respective K values.

I'm pretty sure T1 should always be the initial value and T2 should be the value it is changed to (the resulting value).

KaleenaJezycki_1I

I would assume so because typically they are less than 100 people and they're optional.

KaleenaJezycki_1I

I believe that the elementary steps and indications of which is the fast and slow step will be given and if the slow step isn't given then I think it will be evident with looking at the observed reaction rate at the overall reaction and then writing out the ones for the elementary steps and the rate...

KaleenaJezycki_1I

Can someone explain to me how "take home finals work" how would you turn it in?

KaleenaJezycki_1I

Althea Zhao 1B wrote:The document that Dr. Lavelle shared with us says that the final exam questions will come from the homework. Does this mean all questions will be taken from the homework, or will the format be more like the midterm?

What document are you referring to exactly?

KaleenaJezycki_1I

ASetlur_1G wrote:You add platinum when there's no solid in either the anode or cathode of the cell (like if there's only an aqueous solution). You add it to the side without a solid.

And you can add platinum because it is an inert metal and won't react with anything causing values to change

KaleenaJezycki_1I

You don't need to reverse the reaction because the equation for E^o= E^o(Cathode)- E^o(Anode) using the standard reduction potentials given in the chart. you would flip it if you wanted to add the potentials to get E^o but Lavelle said to stick to one method and stay with it, confusing when to flip ...

KaleenaJezycki_1I

Their reduction potentials give it away. Larger E (naught) = higher reduction potential = increased likelihood of reducing ; therefore, higher E (naught) species gets reduced while the lower E naught gets flipped to get oxidized. If you think about it logically, you can't have 2 reducing species in...

KaleenaJezycki_1I

Can someone please help explain to me why wmax= deltaG? If max work means that 'all' energy released is used for work with no heat transfer then does that imply that delta H =0 and therefore deltaG= -TdeltaS??

KaleenaJezycki_1I

On the "Electrochemistry and its Applications" outline (outline 5) the second bullet says "know the definition of the electromotive force and why it represents the maximum potential difference". I don't remember going over this in class.. Can someone help me with this please?

KaleenaJezycki_1I

For this problem you are asked to write the half reactions of potassium permanganate and Iron (III) Chloride. How are you supposed to know that the Iron is going to go to go from Iron 2+ to Iron 3+ I understand that Iron 3+ comes from the (III) in "Iron chloride" but how do you know that i...

KaleenaJezycki_1I

If both the species are given as "La3+/La and U3+/U" (problem 6M.11) then do you just choose which one you want to be the reducing and oxidizing agent? I don't understand this because they both would be written as reductions.

KaleenaJezycki_1I

Yes, to begin this problem you should know that the Anode is on the right (OXIDIZED) and the Cathode is on the left (REDUCED) so you need to write out the half reactions and then use appendix B to find their Standard Reduction Cell Potentials and then use the equation StandardEcell= StandardE(R)-Sta...

KaleenaJezycki_1I

its the overall change in moles that is always positive, and the equation has a negative in it so it ends up becoming a negative value, when plugged in to the standard gibbs free energy equation.

KaleenaJezycki_1I

It should be the Anode on the left (Oxidized) and the Cathode on the right (Reduced)

KaleenaJezycki_1I

It doesn't matter! Its up to you which one you use but make sure you use the correct conversions for which one you choose (2.303)

KaleenaJezycki_1I

ASetlur_1G wrote:Is it correct to say that G(not) is used at equilibrium (K value) and G is used for other conditions (Q value)?

Yes for the most part.

KaleenaJezycki_1I

Shimei_2F wrote:Because it relates the difference in Standard Gibbs Free Energy to K.

And it will allow you to connect what we are learning in Thermochemistry to acid/base equilibrium, so answering pH questions and etc.

KaleenaJezycki_1I

This is used to display the temperature dependence of K, so it is used when calculating K at different temperatures and can even be used when the question is asking for what the pH is at different temp when given an initial K value. I don't think this is derived for us on the constant sheet so it's ...

KaleenaJezycki_1I

G knot just means that it is only applicable when the elements in the equation are in their standard state since the knot denotes that it is the Gibbs free energy value at standard state. This is true, and also normally when referring to equilibrium constants (K) and equilibrium quotients (Q); Gnot...

KaleenaJezycki_1I

See the Syllabus (which was online about a month before the quarter started). :-) My office hours are W & F 4-5pm (after my last lecture). Click on image to enlarge: Office Hours.png wait Dr.Lavelle has his own office hours?? I thought only his TAs and LAs! Have you been before? Is it helpful?

KaleenaJezycki_1I

Whenever you remove something from a system it shifts toward the thing that was removed to make more of it, because when you remove something you are making less of it and as Le Chateliers principle states, the reaction will do what it needs to to reduce the effect of a force on a system.

KaleenaJezycki_1I

Will it matter on the midterm what we leave our answers in, if not specified explicitly in the problem?

KaleenaJezycki_1I

The state functions one is PDTV HUGS

I forget what he said but I think its something like when I'm Pressured and Depressed, I like to watch TV and get HUGS

P=pressure
D=Density
T=Temperature
V=Volume
H= Enthalpy
U=internal energy
G=Gibbs free energy
S= Entropy

KaleenaJezycki_1I

It is divided in to multiple steps because delta H Fusion only calculates the phase change value. But the solid first needs to heat up to 0.0 Celsius which is one Delta H value and then you must add the n*DeltaHFusion to calculate the Delta H of the overall rxn.

KaleenaJezycki_1I

Also, When is the change in internal energy zero for an irreversible expansion? Internal energy is zero when Temperature is constant because there is no energy transfer if there is no change in temperature ( Internal energy measure the heat transfer) so there is none if temperature isn't changing. ...

KaleenaJezycki_1I

Yes, I believe so and that's why it always says isothermal reversible reaction. I don't think you will see it just say reversible without saying isothermal or constant temperature explicitly stated.

KaleenaJezycki_1I

Constant temperature (isothermal) indicates that delta U is 0. Constant pressure allows you to set q equal to delta H, and the work is -PdeltaV. And internal energy=0 when the process is isothermal because internal energy is heat transfer. So if the temperature is not changing then there will be no...

KaleenaJezycki_1I

Thank you guys so much!!

KaleenaJezycki_1I

STP is 25 degrees Celsius that's why its 298K. At 0 degree celsius its 273.15K because to go from celsius to kelvin you add 273.15

KaleenaJezycki_1I

I believe their explanation was that room temperature= 298K and water vaporizes at 298K therefore you can calculate entropy. I think its similar to the problems we have had where you have to divide entropy up in to steps (since it is a state function) and you can navigate your way to the DeltaSvap o...

KaleenaJezycki_1I

I don't think so, but if it comes up, a rate just means it is per some time measurement. Ex. 26kJ per second

KaleenaJezycki_1I

For the sloped lines in a heating curve ( the solid, or liquid is heating up) for the straight horizontal lines the phase change is occurring. When calculating the sloped lines you use q=mCDeltaT but when you are at a phase change ( straight line), you use n*DeltaHfusion

KaleenaJezycki_1I

You probably won't necessarily need to know them by heart but you can logically think about them while solving the problem, ask yourself how can I make the Gibbs free energy negative and therefor more spontaneous. You do this by looking at the equation algebraically.

KaleenaJezycki_1I

The state functions one is PDTV HUGS

I forget what he said but I think its something like when I'm Pressured and Depressed, I like to watch TV and get HUGS

P=pressure
D=Density
T=Temperature
V=Volume
H= Enthalpy
U=internal energy
G=Gibbs free energy
S= Entropy

KaleenaJezycki_1I

C in Cv is heat capacity and will most likely be the heat capacity of a monoatomic gas : Cv= 3/2R

KaleenaJezycki_1I

Hi! This comes from the original equation deltaH= q+w Step1: isolate q So q=DeltaU-w Step2: To get Delta H we are assuming that the reaction is occurring under constant pressure (qp) Therefore DeltaH= DeltaU-w Step3: BUT w=-PexDeltaV so the we have - -Pex which becomes positive to get: DeltaH= Delta...

KaleenaJezycki_1I

IMG_0853 2.jpg I drew them out so that it's easier to visualize the 12 cis and the 3 trans in case anyone is also struggling like me; the above comment definitely helped me understand this problem a lot better, thank you so much! I circled the X so that it's easier to see how each molecule differs ...

KaleenaJezycki_1I

Sanjana Borle 2K wrote:Yes, in an adiabatic process q equals to zero because there is no transfer or heat between a system and its surroundings.

^^ this correct and then would imply that deltaU (change in internal energy is = w (work)) since q=0

KaleenaJezycki_1I

w as work is presented in Joules or can be kJ if the problem specifies it. W as degeneracy though does not have units because it is just the number of microstates possible.

KaleenaJezycki_1I

So like said above the first part of info (the first q stated) gives us qcal and allows us to solve for the specific heat capacity of the calorimeter. You would do this by using the same equation you stated as q=CdeltaT, but rearrange it as C= cal/delta T. Then you can use this value of C to solve t...

KaleenaJezycki_1I

Can someone please explain what makes a reaction reversible. I am just a little confused about qualifies as a reversible reaction. A reaction is reversible when it is in equilibrium with its surroundings. This occurs when the work is isothermal (at a constant temperature) and the expansion is rever...

KaleenaJezycki_1I

Are you asking for this equation : -nRTlog (V2/V1) or how he derived this?

KaleenaJezycki_1I

I'm not sure if this is the answer you're looking for, but you can't break one bond of a double bond. You have to break the whole thing and reform it as a single bond. You'll have different bond enthalpies for the same atoms bonded with a single bond versus a double bond. ^^ This is true, so you ha...

KaleenaJezycki_1I

It is negative, because bonds are being formed and the rxn is exothermic. Forming bonds is more favorable, because it doesn't require an input of energy breaking bonds does. The reaction being endothermic or exothermic in Thermochemistry is based on what is happening to the surroundings. To break b...

KaleenaJezycki_1I

On part C of this problem, why would the change in internal energy of the system be different then how much work is done in the compression? w= -Pex(deltaV) where Pex= constant external pressure delta V= Vfinal-Vinitial ( the expansion/compressiom of the system) when deltaV is positive , the intern...

KaleenaJezycki_1I

Sorry this is for 4A.1 but I didn't know where else to ask. How can we tell if a system is open, closed, or isolated? Mainly, what is the difference between closed and isolated? I got those two mixed up Micah- a closed system by definition according to the textbook "has a fixed amount of matte...

KaleenaJezycki_1I

Method 2 is the least accurate method but can be used if you are given bond enthalpies. For method 3 everything must be in a standard state and you will receive the standard reaction enthalpy. So I think if it doesn't specify to solve for the standard reaction enthalpy and just asks for the reaction...

KaleenaJezycki_1I

when a chemical equation is written and all the reactants and products are gases, do you use Kp rather than Kc? in what cases do you use Kc rather than Kp? Kc should be used normally, but the question will clarify if it wants molar concentrations or partial pressures. Therefore pay attention to the...

KaleenaJezycki_1I

A closed system cannot exchange mass with its surroundings but it can exchange energy, while an isolated system cannot exchange either. So what would be an example of a closed system and an example of an isolated system? An example of a closed system is an ice pack, like the shakeable ones that are...

KaleenaJezycki_1I

pKa and pKa are the -log of Ka/Kb. You can convert pH to Ka using 10^-ph. You can do the same with pOH by converting pOH to Kb using 10^-pOH. And Just for clarification they are related to pH because they are dissociation constants, they show how much an acid or base dissociate which then determine...

KaleenaJezycki_1I

Lavelle is going to teach us the dynamics of Thermochemistry first so that we have an understandable foundation of what is going on. Then we are going to start calculations, but ultimately everything on the syllabus will covered so just follow what is assigned, it will all be important

KaleenaJezycki_1I

When you reduce a reactant, why does the equilibrium shift in the reverse direction? When you reduce something in the reaction the equilibrium shifts towards it not away from it because now you are making less of that and therefore equilibrium will shift that way to try and reduce the effect on the...

KaleenaJezycki_1I

Adding an inert gas doesn't shift equilibrium because the inert gas doesn't react with anything in the reaction therefore it will be present in the reactants and products equally. However Pressure and and volume will change the concentrations of the system because think about having a big container ...

KaleenaJezycki_1I

delta H has a negative or positive value because it is whether a reaction is absorbing heat (breaking down molecules) or giving off heat (consolidating molecules). If you're going from a solid to gas it will be endothermic and delta H will be positive because you need to break down the solid to tran...

KaleenaJezycki_1I

What makes logical sense for me is to think, pka=-log(Ka), therefore Ka=10^-pka. Then we know Kw= Ka x Kb and so you should rearrange the equation so that Kw/Ka=Kb and now you have your Kb value! Make sure you take it slow and pay close attention.

KaleenaJezycki_1I

Hey, are there any key words or ways to find worksheets that the TAs handed out in their step up sessions? I am unable to attend most of them because I have work.

KaleenaJezycki_1I

Strong acids and strong bases completely dissociate to form ions in solution but weak acids and bases don't completely ionize therefore the reaction is reversible.

KaleenaJezycki_1I

Dina 2k wrote:if a different solvent was used, besides water, would it be included in the calculations?

I believe solvents aren't ever included in the equilibrium constant

KaleenaJezycki_1I

Was this a question assigned in the textbook??

KaleenaJezycki_1I

He'll let us know for sure, but it's all the material covered up until the Friday before the Test. So, for test 1, it will most likely be all the information presented up until this Friday, January 17. Agreed! But to answer your question I would guess no because he will probably cover that when we ...

KaleenaJezycki_1I

Also, the way I think about it is that endothermic reactions like heat because they absorb it, so more heat will help the reaction favor the products. If the reaction is exothermic, it "doesn't like heat" so it lets it go, and wouldn't want to create more products if the temperature rises...

KaleenaJezycki_1I

Where can you view modules? If you enter CCLE and click on Lavelle's chemistry class it will take you to his website where you will type in the password and then scroll down towards the bottom where it says Chemical equilibria Pre-Assessment, video, and post assessment. Lavelle has these modules fo...

KaleenaJezycki_1I

Hi! While I can't find any of his worksheets on Chem Community, it seems that he'll often use worksheets as the backbone of his workshops. Lyndon has workshops in Covel 210 on Mondays from 6-8. If you attend, I'm sure you will receive some of his practice problems. Thank You! I'd love to go to his ...

KaleenaJezycki_1I

Hi! Has Lyndon given out any worksheets yet? If so can someone please share what the key words are to find them? Thank you! ((:

KaleenaJezycki_1I

If a solid or liquid is in the reaction then it does not get represented or more likely it gets counted for as the number 1. However its important to pay attention to the fact that you must stick to the Kc equation of [products]/[reactants] so if the products are both solids or liquids then Kc will ...

KaleenaJezycki_1I

For the modules, if we were given an equation like A (g) + B (g) --> C (s), why do we write the equilibrium constant as 1/[A][B] instead of just [A][B]? I thought we were supposed to just take solids and liquids out of the equilibrium constant. It is still written as 1/[A][B] because A & B are ...

KaleenaJezycki_1I

I believe that Keq is the generalized 'equilibrium constant' but Kc and Kp are forms of Keq (they are not different). Kc refers to concentrations and Kp refers to partial pressures but they both equilibrium constants (forms of Keq).

KaleenaJezycki_1I

Homework will be due Friday in lecture but for the weeks following it will be due in discussion sections. Remember for homework you get to choose your 5 problems to turn in and each week you can turn in problems from a section that is 'relevant' to what we are learning in class.

KaleenaJezycki_1I

If the concentration of a product or reactant is changed while a reaction is in equilibrium, will the reaction then be temporarily shifted out of equilibrium? yes, changing the concentration of the reactant or products will temporarily offset the equilibrium making it shift to the right or left bec...

KaleenaJezycki_1I

sig figs of pH are counted AFTER the decimal point, and this is due to the log function. so if there are supposed to be 3 sig figs the pH in correct sig figs could be 4.567

KaleenaJezycki_1I

Sigma bonds consist of two orbitals, one electron overlap from end to end, and can rotate. Pi bonds also have two orbitals with one electron overlap, but its side by side, and they cannot rotate. In addition to this, know that a sigma bond is a single bond, a double bond has one sigma bond and one ...

KaleenaJezycki_1I

a lone pair acts as other section of electron density in hybridization, so yes they matter. A molecule with 3 bonds and 1 lone pair has 4 regions of electron density and therefore has sp3 hybridization.

KaleenaJezycki_1I

Joseph Saba wrote:Determine it by the intermolecular forces of the molecules as compared with another.

And the stronger the IM forces, the higher the melting and boiling points are because the forces are harder to break to switch in to different phases.

KaleenaJezycki_1I

In the lecture 4's final period the TA was grading the finals as they were coming in, so maybe even sooner. We won't get our physical copies back until next quarter though.

KaleenaJezycki_1I

I got the correct answers for all the parts in 6A.3, yet I wanted to double check to make sure my chemical equations for the proton transfer equilibria were correct because that wasn't in the solutions manual. a) H 2 SO 4 + H 2 O <-> H 3 O + + HSO 4 - b) C 6 H 5 NH 3 + + H 2 O <-> H 3 O + + C 6 H 5...

KaleenaJezycki_1I

Definitely attend as many step-up and workshop sessions as possible. Also join group chats that you can ask questions in, watch videos online, review notes, and fill in the learning objective outlines because then you conceptually know and can explain everything as well.

KaleenaJezycki_1I

Bronsted acids are proton donors and Bronsted bases are proton acceptors. Lewis acids and Bases have to do with non-bonding electrons.

KaleenaJezycki_1I

Coordination numbers are how many bonds (of ligands) attached to the central atom, I don't believe lone pairs count

KaleenaJezycki_1I

Mandeep Garcha 3C wrote:If it is like the midterm, I assume we will not learn anything new on the last lecture before the final.

I believe this is probably very likely, so he may use the last lecture to review but also make sure you attend as many review sessions as you can!

KaleenaJezycki_1I

It should be mostly calculations, but also you should know the quantum world photoelectric effect and descriptions of trends and so on. Its fair game to be asked to explain IM Forces and other things.

KaleenaJezycki_1I

F is more electronegative than Cl so it is less likely to give off the H+ ion. This means that HCl can disassociate easier, making it the stronger acid. This exactly explains why, but in addition HCl is a stronger acid than HF because HCl has a longer/weaker bond between the H and Cl making it easi...

KaleenaJezycki_1I

I feel like we won't be given this chart and will have to know the general trends, hopefully after a lot of practice these rules pf prefixes and suffixes will start to become routine is the goal I would assume.

KaleenaJezycki_1I

Are you guys still meeting??

KaleenaJezycki_1I

Will we have to use this equation on the test at all??

KaleenaJezycki_1I

Does anyone have any extra worksheets or resources to get more practice of the material that is going to be on Test 2?

KaleenaJezycki_1I

tonyhu wrote:Is hybridization going to be the main topic on test 2?

Hybridization will not be on the test. I would not focus on studying this until after the test, focus on the topics from 3F.4, 3F.5, and 2E-F

KaleenaJezycki_1I

205192823 wrote:So do we technically need to do chapters 2D, 2E, and 2F, since the midterm was up until 2D right?

Also section 3F.4 and 3F.5 !!

KaleenaJezycki_1I

2E.3.A asks for the molecule HCN, not NH3, is that correct? In this case you would first draw the lewis structure that is C as the central atom connected with a single bond to H on one side and a triple bond to N on the other side and N has 1 pair of lone electrons. Then the shape is Linear because ...

KaleenaJezycki_1I

Because it is ClO2+ ion there are 18 valence electrons because the + means to subtract 1 electron. Therefore draw the lewis structure with Cl as the central atom and O atoms connected by double bonds to Cl, then 2 sets of lone electron pairs on each O and 1 set of lone electron pair on the Cl. Then ...

KaleenaJezycki_1I

A central atom with four bonding regions will always be known as a tetrahedral for its domain geometry BUT if there are lone pairs attached to the central atom this will change. Eventually we will cover molecular geometries which will allow us to name molecules with lone pairs attached to the centra...

KaleenaJezycki_1I

I believe we will learn these terms on Friday in Lecture and eventually they will be what we name our VSEPR models as, because they are more specific and telling of the actual shape of the molecule.

KaleenaJezycki_1I

Because IF4- has 4 bonding sites and 2 lone pairs of electrons, it technically has 6 regions of electron density. Since there are 6 regions of electron density then the Domain geometry is Octahedral, but the Molecular geometry is Square Planar due to the 2 lone pairs. We have not yet covered this in...

KaleenaJezycki_1I

Count the bonds around the atom as 1 electron and then count each lone pair as 2 electrons (count each dot you drew individually) and you want this to add up to the number of valence of electrons of the actual element. However if this is on a test then you should show the actual calculation.

KaleenaJezycki_1I

To go from Atoms to moles you take the number of atoms and divide it by avogadros number over 1 mol then you can convert it to what every molecule you need.

KaleenaJezycki_1I

Fluorine is the most electronegative element. Electronegativity decrease down a column and across a row (right to left). Or oppositely it increases up a column and left to right across a row.

KaleenaJezycki_1I

Write a balanced combustion reaction for solid nicotine (C10H14N2). (Hint: The reaction produces N2 gas). How can we balance it when both sides don't have Oxygen? Or does it? How are we supposed to figure this out? Combustion reactions always are a compound +O2 and produce CO2+H20 So this should lo...

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