CHEMISTRY COMMUNITY

Kandyce Lance 3E

I think you meant to write 2HD (g)--> H2 (g)+ D2 (g) When you increase the pressure of the system, you expect the reaction to favor the side with the less moles of gas to relieve the pressure (Le Chatelier's principle). However, in this case, there are 2 moles of gas in the reactants and 2 moles of...

Kandyce Lance 3E

Victor Qiu 1C wrote:I think the values are:

1 atm = 101325 Pa = 101.325 kPa = 1.013 bar = 760 torr

What did you use to get those values?

Kandyce Lance 3E

Marylyn Makar 1B wrote:Hi! Yes the denominator would be 1

and what would it be if they were gasses?

Kandyce Lance 3E

What key words should we look for in order to determine if we should be using Ka and Kb? This concept caused me a few issues with the homework In the homework, you'd need to use Ka when solving for a weak acid, and Kb when solving for weak bases. You solve for one by dividing 1x10^-14 by the other....

Kandyce Lance 3E

Hi Lexy! This personally how I went about solving this problem: 1. Since Kb is given to you in this problem and the constant for Kw is known as 1.0 x 10^-14, I solved for Ka using the equation: Ka x Kb = Kw. 2. Once you calculate the value for Ka, you should notice that it is significantly small; t...

Kandyce Lance 3E

Ken_Cheng_2A wrote: $\Delta G = \Delta H^{\circ} - T\Delta S^{\circ},$ is the formula that directly relates Gibbs free energy to enthalpy and entropy.

How can we find deltaS if its not given?

Kandyce Lance 3E

Alysa Rallistan 2G wrote:The problem will explicitly state it or you could be shown the values

Are there any "intermediate" time reactions?

Kandyce Lance 3E

Shally Li 2C wrote:Rate laws are determined experimentally, so they will be given. You cannot determine rate law from chemical equation unless it is an elementary reaction.

what do you mean by elementary equation?

Kandyce Lance 3E

Nathan Mallipeddi 2H wrote:I believe enzymes may be both homogeneous and heterogeneous. There are many enzymes there are heterogeneous in various biological contexts.

Do you have any examples of heterogeneous enzymes?

Kandyce Lance 3E

How often does it update? If its been updated for Midterm 2 i don't have to worry about it for the final right? Usually you don't have to update it too often I believe, but to be safe I would if there's an update. ok and do we need to look for updates? or when we open the lockdown browser it well p...

Kandyce Lance 3E

Nick Pascua 2L wrote:Hello,

The electromotive force (EMF) is not always equal to the maximum potential difference, but when it is equal, the current flow is cut off and no energy is passing through.

If no energy is passing through does that mean it's also at equilibrium?

Kandyce Lance 3E

Jessie Hsu 1C wrote:Yes! And for reference standard conditions refer to 1M or 1ATM at 298 K

If at least one of these arent like you said we assume the reaction isn't occurring in standard conditions?

Kandyce Lance 3E

DMaya_2G wrote:The voltage of the cell is connected to the concentrations, which is seen by the equation E = E* - (RT/Fn)lnQ. Both Q and E are concentration-dependent.

What do we need to do when we don't know E*?

Kandyce Lance 3E

Faith St Amant 3D wrote:The dot in between the Fe2O3 and 3H2O (Fe2O3∙3H2O) indicates that they form one compound, so the stoichiometric coefficient in front of the iron applies to the entire term. Hope that clears things up:)

Thank you so much for clearing that up!! I wasn't sure what that dot was for

Kandyce Lance 3E

Can someone also explain the order we should short hand notations when writing the full reaction of salt bridge questions?

Kandyce Lance 3E

How often does it update? If its been updated for Midterm 2 i don't have to worry about it for the final right?

Kandyce Lance 3E

What about 14BL? Its closed and im not sure if there is a waitlist or not. Do i have to wait another quarter tot ake it?

Kandyce Lance 3E

Bella Townsend wrote:In general short reactions favor kinetic control, while long reactions favor thermodynamic control.

This is really helpfull and straightforward thank you!!

Kandyce Lance 3E

Make sure to treat yourself a little!! Midterms can be stressful :)

Kandyce Lance 3E

Im eating dinner rn, having that food so not my favorite food ever but my favorite Thai dish is chicken Pad Thai

Kandyce Lance 3E

No problem, better late than never right? lol. Thanks so much for still responding :)

Kandyce Lance 3E

I think these jokes are sodium funny. In fact, I slapped my neon that one!

Kandyce Lance 3E

Also make sure to have your signs correct before doing e^()!! I made that mistake when solving this problem and got a drastically different answer.

Kandyce Lance 3E

While solving a problem, I think having all of the quantities in similar units is a must. So, I like to convert joules to kilojoules or vice-versa before starting the calculations so that it becomes easier to solve the problem without making mistakes. And if you write and cancel out your units only...

Kandyce Lance 3E

Awesome , thank you!!

Kandyce Lance 3E

For the constant pressure, why do we multiple 7/2?

Kandyce Lance 3E

Is isothermal just another way of saying no change and that's why it can also be referred to as reversible?

Kandyce Lance 3E

Kandyce Lance 3E wrote:Is that same reason why even of we get a negative calorimeter constant we change the sign no matter what?

To clarify I mean because calorimeters absorb heat?

Kandyce Lance 3E

Is that same reason why even of we get a negative calorimeter constant we change the sign no matter what?

Kandyce Lance 3E

I have a follow up question for that problem, after getting my values for q, why are q and deltaU

Kandyce Lance 3E

Gicelle Rubin 1E wrote:I know it's a bit repetitive hearing the same thing but a state function means that, in order to determine its value, we only need both the initial and final state.

and then we also subtract final minus initial right?

Kandyce Lance 3E

Crystal Pan 2G wrote:When bonds are formed, energy will be released which would make it exothermic. When bonds are being broken, energy is required to break them, which means it is endothermic.

Does that also mean more energy is needed to break vs form reactions or is it dependent on specific chemical reactions?

Kandyce Lance 3E

Are step up sessions available during holidays since they are semi-unofficial?

Kandyce Lance 3E

I feel the most frustrating is when I do my calculations only to find none of the options match.

Kandyce Lance 3E

If we were on campus would we be using calorimeters in discussion or possibly Chem14BL?

Kandyce Lance 3E

Hi Lexy! This personally how I went about solving this problem: 1. Since Kb is given to you in this problem and the constant for Kw is known as 1.0 x 10^-14, I solved for Ka using the equation: Ka x Kb = Kw. 2. Once you calculate the value for Ka, you should notice that it is significantly small; t...

Kandyce Lance 3E

Would remembering the strong acids and bases be helpful for the midterm? or would the elements be specified in the questions similar to out hw

Kandyce Lance 3E

For this problem, are [OH-] and [BH+] interchangeable ?

Kandyce Lance 3E

What key words should we look for in order to determine if we should be using Ka and Kb? This concept caused me a few issues with the homework

Kandyce Lance 3E

Hi! First we need to note that the chemical reaction for a weak acid is: HA(aq) + H20 (l) <-> A-(aq) + H3O+(aq), Ka = [HA]/[A-][H3O+] = .00474 Next, we need to set up our ICE table: HA <-> A- H3O+ I .159 0 0 C -X +X +X E .159-X X X Once you solve for X, put X/.159 to find the percent ionization. Ho...

Kandyce Lance 3E

I agree with the replies above; one thing to note is that Kw is only 10^-14 when the temperature is at 25 degrees Celsius. Is there a constant value for Kw at other temperatures that we will be using in chem? Or is Kw at 25 degrees Celsius the only constant we know so if the example given isn't at ...

Kandyce Lance 3E

705340227 wrote:Also, the exothermic/endothermic properties of the reactions determines how the temperature is going to affect K.

Do you mean affecting the K value as it being larger or smaller? I have in my notes that reaction properties affect K values for temperature as well but I'm not sure how exactly

Kandyce Lance 3E

Can someone specify how we know when to assume the change in X is negative or positive when using the Ice Box method please? I ran into some trouble on the homework a few times because I had the wrong signs for X.

Kandyce Lance 3E

You are right in that Kc is used when molarities/aqueous solutions are involved and Kp is used for gases/partial pressures. However, if you were to use the ideal gas law you could convert those molarities to partial pressures and find the respective Kp value. The same goes for converting partial pr...

Kandyce Lance 3E

Does someone mind explaining what to do witht he reverse of that question ^? Like when you end up with two negative answers. Or is that typically a red flag and the work should be checked?

Kandyce Lance 3E

If a reaction is endothermic than it requires heat to get to the products so adding heat is favoring the products. If a reaction is exothermic, that is saying the same thing as the reverse reaction is endothermic so increasing temperature favors the reactants. So because reactions can be reversed, ...

Kandyce Lance 3E

If a reaction is endothermic than it requires heat to get to the products so adding heat is favoring the products. If a reaction is exothermic, that is saying the same thing as the reverse reaction is endothermic so increasing temperature favors the reactants. So because reactions can be reversed, ...

Kandyce Lance 3E

Nathan Lao 2B wrote:Basically, an inert gas is any of the noble gases. It's considered "inert" because most of the noble gases do not react.

Thank you!! I didn't realize it was just another word for "noble". Thought it was a completely different concept lol

Kandyce Lance 3E

I believe the formula for converting Kp to Kc is

Kp= Kc(RT)^ delta n

i'm not entirely familiar with this concept however, so anyone feel free to correct me if i'm wrong

Kandyce Lance 3E

What is an "inert gas" and what makes certain gases inert? Professor Lavelle used this term in lecture and I'm not familiar with it

Kandyce Lance 3E

Kandyce Lance 2L wrote:are we expected to know all the exceptions for the final? or is it fine if we know how to find EC?

Would it be a better idea to try and learn them all anyway?

Kandyce Lance 3E

are we expected to know all the exceptions for the final? or is it fine if we know how to find EC?

Kandyce Lance 3E

The atoms in the molecule with the highest electronegativity will pull the electrons more, creating a negative dipole at that atom. And since that atom is pulling electrons, other parts of the molecule will have a positive dipole since electrons are being pulled away from them. To draw the arrow, t...

Kandyce Lance 3E

Kandyce Lance 2L wrote:So Lewis and Bronsted acids/bases are only opposites or different from each other in the context we are defining a molecule?

In terms of the bronsted definition being focused on protons instead of electrons?

Kandyce Lance 3E

So Lewis and Bronsted acids/bases are only opposites or different from each other in the context we are defining a molecule?

Kandyce Lance 3E

Daniela_Martinez_3B wrote:The organic chemistry tutor on youtube has a great video on sigma and pi bonds that really helped me visualize them!

Do you mind sharing the link to the video that helped you?

Kandyce Lance 3E

reva_bajjuri wrote:so for the above ethylene structure are all of the hydrogens in the same plane?

Yes thats correct!

Kandyce Lance 3E

I noticed that acid rain has a range of pH levels but in some cases its as acidic as beer but i don't believe it ranges above that, either way does that mean acid rain isn't painful/harmful on skin? the name is intimidating but is it only as effective as spilling beer on skin maybe?

Kandyce Lance 3E

105289321 wrote:If an atom can donate more than one H+

Do you have an example of this?

Kandyce Lance 3E

Praneetha Kakarla 1E wrote:Just to add onto what Mikayla said, something that helps in figuring out conjugates when looking at a chemical reaction is knowing that conjugates differ by one proton (like NH3 & NH4+).

That makes so much sense thank you!!

Kandyce Lance 3E

Ryan_Kien_1L wrote:I personally think that it depends on your definition of acids and bases (ie. Bronsted-Lowry, Lewis, Arrhenius). So the first thing you'd need to do is identify which definition you're looking for.

Do you mind writing out those definitions please?

Kandyce Lance 3E

Olivia Smith 3B wrote:A quick way to figure out hybridization is to count all of the electron density areas, subtract by one and that will be the exponent if you will of the hybridization.

I use this trick too, but I'm not sure why we subtract one, can you explain that a bit please?

Kandyce Lance 3E

Sejal Parsi 3K wrote:Thought there are dipole moments happening between atoms in a molecule, they can cancel out, making the molecule non polar.

Yes! that's true

Kandyce Lance 3E

David Liu 3B wrote:like lavelle said in lecture, I feel like it's important to note that the "normal" elements we use generally follow the trend, but any element that has access to the d orbital past period 3 can generally overcome the octet rule

Ok great, thank you!

Kandyce Lance 3E

Is it possible to have two different resonance structure that are equally "most beneficial"? For example moving the position of a double bond has the same exxfect for each position bc they dont affect formal charge? Just the position of the charges?

Kandyce Lance 3E

Oxidation numbers, also called oxidation states, are the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. An oxidation number can be assigned to a given element or compound by following the following rules: - The oxidation number of a ...

Kandyce Lance 3E

I have an additional question relating to bond angles, For two molecules with the same shape (like an AX_3 for example), will all the bond angles be the same? Or will they change depending on the individual elements? I understand bond angles with be slightly different with lone pairs vs no lone pai...

Kandyce Lance 3E

I was having some trouble drawing lewis structures recently because I would often find myself with (usually 2) extra electrons. After I had already filled the outer elements to 8. It was in a recent lecture that Dr. Lavelle put the lone pairs on the elements in the middle and I never thought to do ...

Kandyce Lance 3E

I was having some trouble drawing lewis structures recently because I would often find myself with (usually 2) extra electrons. After I had already filled the outer elements to 8. It was in a recent lecture that Dr. Lavelle put the lone pairs on the elements in the middle and I never thought to do t...

Kandyce Lance 3E

I have an additional question relating to bond angles, For two molecules with the same shape (like an AX_3 for example), will all the bond angles be the same? Or will they change depending on the individual elements? I understand bond angles with be slightly different with lone pairs vs no lone pai...

Kandyce Lance 3E

I have an additional question relating to bond angles, For two molecules with the same shape (like an AX_3 for example), will all the bond angles be the same? Or will they change depending on the individual elements?

Kandyce Lance 3E

These responses are a bit mixed but I agree, it would be safest to memorize the basic bond angles in the common geometric shapes and planars

Kandyce Lance 3E

Jordanmjones13 wrote:Do you know if the problems will specifically tell us how many significant figures to use?

I believe you use the lowest number of sig figs gives from numbers in the question

Kandyce Lance 3E

Since ice is less dense than water, it floats but in alcohol it sinks so is that because alcohol is more dense than ice and also alcohol also takes a very long time to freeze, is this because of the density, or it it caused by hydrogen bonds?

Kandyce Lance 3E

He subtracted 1 electron because the ammonium had a positive charge. This means the ammonium had to lose 1 electron to be positively charged. Thank you! I went back to my notes and I missed where it said -Cation: remove 1e- for each +1 charge -Anion: add 1e- for each -1 charge In case anyone else h...

Kandyce Lance 3E

My question has more to do with orbitals as a concept, but on a recent lecture Professor Lavelle states that "An orbital is a math function with three quantum numbers: n,l,m" I was a bit confused because I thought orbitals were work functions, not math functions...are they both the same t...

Kandyce Lance 3E

Ammonium, NH₄⁺
N- 5e-
O- 1e- x 4 = 5
then add
5 + 4 = 9
but in this example we ended up with 8e-

In the Ammonium example from lecture why did Dr. Lavelle subtract 1 to get 8e-? I thought we were just adding..

Kandyce Lance 3E

From lecture, Dr. Lavelle used this example to show that removing the 2nd e- will always take more energy Cu(g) --> Cu^+(g) + e-(g) l_1 = 745.1 kJ.mol^-1 Cu^+(g) --> Cu^2+(g) + e-(g) l_2 = 1955 kJ.mol^-1 (almost 3x harder) Where is the formula to find the ionization energy? Or is the ionization for...

Kandyce Lance 3E

From lecture, Dr. Lavelle used this example to show that removing the 2nd e- will always take more energy

Cu(g) --> Cu^+(g) + e-(g) l_1 = 745.1 kJ.mol^-1
Cu^+(g) --> Cu^2+(g) + e-(g) l_2 = 1955 kJ.mol^-1 (almost 3x harder)

Where is the formula to find the ionization energy?

Kandyce Lance 3E

SahajDole_1G wrote:The 4s shell has a lower energy level than 3d, which is why the 4s shell fills first

So basically, the takeaway from this question is that it doesn't necessarily matter the number being filled in the shell but the energy level?

Kandyce Lance 3E

Yes you can have the same 3 quantum numbers since each orbital can hold two electrons. Thus, two electrons in the same orbital would have the same first three quantum numbers but have a different spin state. This is just a clarifying question, but with the last 2e- on the same orbital, one will spi...

Kandyce Lance 3E

My question has more to do with orbitals as a concept, but on a recent lecture Professor Lavelle states that "An orbital is a math function with three quantum numbers: n,l,m" I was a bit confused because I thought orbitals were work functions, not math functions...are they both the same th...

Kandyce Lance 3E

Kandyce Lance 2L wrote:Can someone clarify expand on why there can be no more than 2e- per orbital?

Does it have to do with not being able to have the same 4 quantum numbers? or are those two topics unrelated?

Kandyce Lance 3E

Can someone clarify expand on why there can be no more than 2e- per orbital?

Kandyce Lance 3E

Can someone explain why there's an inverse relationship between the certainty of momentum and position for electrons? Based on these responses i understand that as the uncertainty for position goes up, uncertainty in momentum will go down and vice versa but additionally is there anyway the level of...

Kandyce Lance 3E

I also have a question regarding orbitals. From my notes in a previous lecture i have it written that when n=2, l=1 ml=-1 that the electron is in "a 2px state" and i went back and rewatched that portion of th electure but i dont understand what the "px state" is referring to. Doe...

Kandyce Lance 3E

I forgot to mention that after i would use E=n^1-n^3 and lambda=h/m*v? This is my process when solving this equations so I'm not sure if my calculations are wrong, or if my general set up is. Any guidance is very much appreciated!

Kandyce Lance 3E

Calculate the wavelength, in nanometers, of the spectral line produced when an electron in a hydrogen atom undergoes the transition from the energy level n=3 to the level n=1. for this question we assume that equation is set up as E=3 is 1/8hR and E=1 is 1/2hR? because that's how i set up this probl...

Kandyce Lance 3E

I'm not sure if i have this written wrong but i was going through some notes and i noticed i have debroglies equation written as lambda = hc/p but im not sure where the speed of light comes in. does someone mind explaining that?

Kandyce Lance 3E

What was the original metal used in the photoelectric effect? Is that a known fact and is it copper which is why it's used in most of the videos on it, or is copper just a more familiar stand in for the actual metal used?

Kandyce Lance 3E

In the Atomic Spectra video we had to watch, in the key concepts it says that Rydberg's constant is 3.29x15^15s^-1 but at another point in the video Prof says its 3.29x15^15 Hz. Can someone explain the difference between the units, or why there is no difference? I believe that Hz is a derived SI un...

Kandyce Lance 3E

I noticed in a previous lecture when prof was going over the equations like E=hv or c=λv the letter "v" was written with a bit of a curve. Is this intentional so we know that this V is referring to frequency and not velocity as it would in other equations, or is that just prof's handwriting?

Kandyce Lance 3E

When regarding temperature, do we not say something is 273 /degrees /Kelvin, as we would with Celcius and Farenheit? We leave out the "degrees"?

Kandyce Lance 3E

From the atomic spectra video, the Borh's Constant equation En=hR/n^2, I don't understand why the value of n being a large number would make En a small number. If I were to plug in real number would this concept become more clear?

Kandyce Lance 3E

In the Atomic Spectra video we had to watch, in the key concepts it says that Rydberg's constant is 3.29x15^15s^-1 but at another point in the video Prof says its 3.29x15^15 Hz. Can someone explain the difference between the units, or why there is no difference?

Kandyce Lance 3E

I went to a workshop and someone asked this question, and the UA ended up saying that the molar mass should have been given because there would have been no way for us to find it. I ended up pressing the give up button on that one. I was able to find the theoretical yield but couldn't for the life ...

Kandyce Lance 3E

This is just a short anecdote but in sophomore year of high school I tried learning the "Periodic Table Song" by ASAP Science and I still haven't learned the full thing. I know up too 104 before it gets to fast and I can't keep up. T-T I hope one day I can do the whole thing.

Kandyce Lance 3E

For the people that have utilized the step up sessions and online resources, how helpful are the sessions in comparison to other resources? Is there an overall preference that works for the set up of this class, or would it just depend on the individual.

Kandyce Lance 3E

I also had trouble determining how to approach this question, but this thread was very helpful. I think it was really key to understand how to use the grams of products given to find the mass and moles of C, H, and O. From there, the rest of the problem was generally straight forward! I actually ha...

Kandyce Lance 3E

How do I register or join a step up session online? See my class website at: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/Chem14UA_PL_ALL.pdf 40 hours per week. Click on the zoom link for those you want to attend. Organized and Easy :-) Just to clarify, we don't actually have t...

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