CHEMISTRY COMMUNITY

Joseph Lee

pH really only factors in the H+ concentration while the pKA will look at the entire equilibrium reaction.

Joseph Lee

Horrible!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Cannot wait for general chemistry to be over.

Joseph Lee

You actually don't balance H+, you balance the OH- (a good tip of balancing is make sure that the OH- is double the H20 amount)

Joseph Lee

You have to write out the half reactions but if you want to remember really easily

RE-duction has electrons on the side of the RE-actants.

Joseph Lee

When writing in shorthand I believe that you separate all on one side of a salt bridge with a solid line and the salt bridge is a double solid. I don't really understand where the commas play in to be honest though...

Joseph Lee

It's the same thing! Just make sure that you are sure of the units that are being used, n usually refers more to molarity and concentration while m usually refers to mass, which would be in grams. As long as the units for the specific heat matches, you are good.

Joseph Lee

Extensive property describes something that is affected by the amount of something. Enthalpy and entropy are examples of extensive properties. Electrical potentials are not extensive.

Joseph Lee

They are the same thing as each other! Galvanic = Voltaic

Joseph Lee

You can calculate G or you can look at the components of G, which are the enthalpy and the entropy and the temperature.

Joseph Lee

The steam is at a much higher temperature, and has much more energy than water, and thus can cause much more severe burns.

Joseph Lee

Water can be held at 100 degrees C without turning into its gaseous form. It can then be turned into gas with the addition of more heat (enthalpy of vaporization).

Joseph Lee

It'll be pretty much the same exact thing as last quarter! Online and on zoom.

Joseph Lee

Bomb Calorimeters are isolated systems and have their own heat capacities! That latter part took me a while to figure out.

Joseph Lee

Work: neg = work done by system, pos = work done on system
Gibbs Free Energy: neg = spontaneous, pos = not spontaneous
Enthalpy: neg = exothermic, pos = endothermic
Potential: neg = not spontaneous, pos = spontaneous

If there are any that I missed let me know!

Joseph Lee

It's just the number of (moles of) electrons

Joseph Lee

It's just that you use H+ ions instead of OH- ions to balance the half reactions!

Joseph Lee

The negative sign is always there! Just make sure that you put the right volumes where they're supposed to be! The final should always be above the initial

Joseph Lee

I also remember that a lot of the times that we use this reaction, we're talking about how the increase of temp in one system affects the other. Example: when you add cold water to hot water and want to see the final temperature you have to use the qc=-qh equation.

Joseph Lee

Think of it in the direction that you're moving, vaporization moves upwards since its getting hotter, which means that the enthalpy is positive.

Joseph Lee

Whenever pressure comes into play, make sure you're using the 0.08206 with atm, but if not, it is usually referring to 8.314 value. Just make sure to look at the units and seeing if they properly cancel each other out. I know it seems like a lot of work but it does help make you gain confidence.

Joseph Lee

The oxidizing agent is in the reduction reaction, which means that the compound that gains electrons is the oxidizing agent (because it technically oxidizes the other half reaction).

Joseph Lee

Yeah haha every person I know got that email, I'm not sure what it is but I guess just don't click on it?

Joseph Lee

You manipulate K! So however the equation is "multiplied" that is the exponent that you apply to the K value. In this case, assume that multiplying something by a negative flips it.

Joseph Lee

Anode is Oxidized, Cathode is reduced! if you need something to think, just remember that the vowels stick together. Also Reduced starts with R which is why it is on the RIGHT side of the R-L equation

Joseph Lee

Anode is Oxidized, Cathode is reduced! if you need something to think, just remember that the vowels stick together. Also Reduced starts with R which is why it is on the RIGHT side of the R-L equation

Joseph Lee

They'll specify for you if it is basic or if it is acidic but just know that for acidic, add as many water molecules as oxygen you need on one side, and then just balance the other side with H+ ions. For basic solutions, add twice as much OH- that you need on the side that doesn't have enough oxygen...

Joseph Lee

Think of it like equilibrium, if I add something to one side, the other side is going to have a boost in production, and the concentration for the reactants on the same side will be lower in comparison.

Joseph Lee

Yeah you're right, we only really use them for ideal gases, and they also must be monatomic too since diatomic is 7/2R and 5/2R instead.

Joseph Lee

Polyethylene is a solid!

It's basically like explaining that ice or rock has a lower entropy than water vapor or air, the gas is more "disordered" and thus has a higher entropy

Joseph Lee

You just look at the atoms attached to it and set the charges = 0 (or whatever the charge of the molecule is)

MgO2 would be like (x) - (2*O2) = 0

and we know O2 = -2, so Mg's oxidation number must be 4

Joseph Lee

It honestly is just kind of what it sounds like, reversible would usually be done in an isolated system where nothing can leave or be added and so everything stays the exact same as it is initially, whereas irreversible can also be like in this environment, but usually is less efficient and faster.

Joseph Lee

n stands for the number of moles but for electrochemistry, it stands for the amount of electrons used up in each half reaction

Joseph Lee

It ALWAYS helps me to look at the units of the calculation and see what I should be having as a result, it shows me which numbers I can plug into where, which has shown me which equations I should use to calculate problems.

Joseph Lee

Inert is just a filler gas that doesn't really react, and thus doesn't contribute anything to the reaction

Joseph Lee

I always found it just the easiest to see the reactant of the reduction (oxidizing agent) and the reactant of the oxidation (reducing agent). It's just an opposite thing.

Joseph Lee

If you decrease the volume, the reaction with more moles will start working overtime, and thus the reaction that produces less moles will actually have an increase. Vice versa

Joseph Lee

Thanks! I keep on forgetting how affecting the concentrations will make differences, so this broke that concept down really well!

Joseph Lee

an SHE is basically just what you use to find the voltage/potential of a specific reaction. You use it with another half reaction because it will make it so that you only have to focus on the one you're looking for (in like a laymans term)

Joseph Lee

Yep! If delta G is negative, that means there's an excess of energy that can be used, which means that it was spontaneous, and because of the equation G=-nfE, E must also be positive for it to be spontaneous

Joseph Lee

Ka is the actual constant and pKA is the negative log of that

Joseph Lee

This is because if you set up your icebox, you will find that the initial concentration of the reactant usually gets 'x' subtracted from it to show how it was used up during the reaction toward equilibrium. That is why when you find the final equilibrium concentration, you have to add the amount tha...

Joseph Lee

the first midterm is said to be on wednesday, feb 2nd

Joseph Lee

No you omit H20 in the ICE tables because it is almost always in excess and so it will not contribute to the reaction's concentrations

Joseph Lee

-log[Ka] = pH

-log[Kb] = pOH

-log[Kc] = pH or pOH (depends on whether it is a weak acid or base reaction

Joseph Lee

Only the ones that are both aqueous as reactants AND as products can we say are "fully dissociated" and we use in the constant calculation

Joseph Lee

Yep! When the reaction quotient is the same thing as the equilibrium constant, then the reaction is at equilibrium.

Joseph Lee

Le Chatelier's principle is pretty simple overall, it just describes that in a closed system, manipulation to a part of the reaction (whether forward or backward) will somehow affect another aspect, since nothing can really be added or taken away in that reaction.

Joseph Lee

Q refers to the overall reaction quotient BUT does not refer to the equilibrium constant. Think of Q as K, but without having actually gotten to equilibrium, thus the number that you get wouldn't be the equilibrium constant. Since this is the case though, it can be calculated at any point in the rea...

Joseph Lee

Also a tip if you've already worked through it or not, make sure that the (2x) is squared, so it should be 4x^2 or (2x)^2 rather than just 2x^2. Hope this also helps

Joseph Lee

You could have a different number in front of the hybridization, but since we're really only dealing with group 2 most of the time, you don't really need to add it in front. It's just more for specificity.

Joseph Lee

Well technically CH2FCOOH is also a weak acid too, so we're all talking about in terms of weak acids. However, the Flourine in CH2FCOOH delocalizes the electrons further so that in the conjugate base, when the H is taken off, the structure is more stable and its electrons are delocalized more.

Joseph Lee

With pKa, it's similar to pH in the sense of its trends. The lower the pH and pKa, the stronger the acid and higher the [H3O+] for pH and higher the [Ka] for pKa.

Joseph Lee

I'm not exactly sure this time around but apparently in years prior, our TA told us that it was 30 6-point questions and was out of 180 points. For us, it's out of 140 but I'm assuming that we might also have around 30 questions that are mixed with 4 and 8 points? Or maybe 25. It could very well be ...

Joseph Lee

The conjugate acid of a base, is for example NH3. If NH3 were to be put in a reaction with water, it would form NH4+ and OH-. The NH4+ is a conjugate acid, since it is the acid that forms from the base NH3 in water.

Hope that makes sense!

Joseph Lee

Hello! Ligands are simply just things that bind to a central atom. They are just used as ligands because they may have multiple binding sites and also because they are full molecules. Mostly though it's just jargon.

Joseph Lee

The hybridization of BeCl2 is SP

Joseph Lee

Sigma bond = single bonds

Pi bonds = anything thats more than that.

AKA

Single bond = 1 sigma bond
Double bond = 1 sigma bond + 1 pi bond
Triple bond = 1 sigma bond + 2 pi bonds
Quadruple bond = 1 sigma bond + 3 pi bonds

Joseph Lee

I love french onion soup. I will die for it. Literally.

Joseph Lee

you just use the logarithm equation he gave us in class today! make sure you use the negative though since we're taking the log of a concentration which is really small, so it would be at a negative power.

Joseph Lee

Bigger atoms = more electrons = stronger LDF because that's how they interact.

Joseph Lee

F is the most electronegative, and so they would attract the electrons the most, meaning that they have the most negative charge within the molecule.

Joseph Lee

Most of the time it depends, if we are talking about hypervalent models, then you try to go for many different combinations, but still try to minimize formal charges. With regular octet structures you try to make it so that the central atom does not have any formal charges. A good rule of thumb is j...

Joseph Lee

Ionic bonds form through positively and negatively charged ions. Thus, because it is just by that rule, it is easier to create networks of ionic bonds. This lattice is overall stronger than the covalent bonds, and is harder to break.

Joseph Lee

A will almost always be one, so it is just denoted by A since there is no point in writing A1.

X denotes the amount of bonding pairs on the central atom.

E denotes the amount of lone pairs on the central atom.

Hope this helps!

Joseph Lee

Halides are just the second to last group (column), right before noble gases, in the periodic table.

Joseph Lee

To add on, the bent shape is created because of its tetrahedral properties, so you can think of bent to have that similar shape. Pretend you were to take off two molecules in a tetrahedral shape, no matter where you did it, it would look like a bent molecule.

Joseph Lee

Yep, all molecules have London Dispersion Forces, and can then have different ones like dipole-dipole or ionic or etc.

Joseph Lee

I'm unsure, I think it might be similar to how the midterms are administered, but I also remember that the final is being taken at the same time by everyone, so it might be online on zoom. Probably just email or ask your TA though, they should be able to give you the best answer.

Joseph Lee

You honestly don't know accurately so you kind of just have to use your intuition about what you already know about those atoms according to their nuclear charge and radius.

Joseph Lee

I dressed up as wet floor sign and poured water on the floor with my squirt guns/water bottle. Incredible costume. Got many compliments.

Joseph Lee

This sounds stupid, but work with someone who will keep you accountable while using a modified version of the pomodoro method. Set a timer for each other and don't speak, and then talk for a bit, and then set another timer. If I stick to it, it always works for me and I feel like I get a lot of work...

Joseph Lee

More electrons usually mean that there will be more van der waals forces, which creates a stronger and more tightly compact atom/molecule. That's why the larger atoms with more electrons tend to be solids.

Joseph Lee

I don't know if you remember the example he gave, but N2 is a really good one that represents induced dipole-induced dipole bonds.

Joseph Lee

Hello! We covered this in lecture today, but shorter bond lengths mean that there is a stronger attraction, while longer ones usually tend to mean that they are weaker. Also double bonds are rarely broken for reactions, while longer and single ones are. And don't forget, electron electron repulsion ...

Joseph Lee

You can just think of any resultant anion as an acid "A to A" and cation to base (no mnemonic for that but it's just there). Other than the extent of that though, you don't really have to memorize the lewis acids and bases.

Joseph Lee

I get that it's a little confusing, but most of the times, in an equation, you refer to the amount of electrons that are lone pairs. Also they kind of just call it that because it's almost always found as pairs (if they weren't it'd be pretty unstable like how it would be in a radical).

Joseph Lee

It is simply referring to the electron within an atom with resonance. You can't really "localize" it, which is why it's called that

Joseph Lee

In the same way, a hydrogen bond is technically a dipole-dipole bond, but just especially between hydrogens. The concept remains the same though, if that helps you visualize it in your head.

Joseph Lee

Stop because all I remember was that he said that the amplitude is directly proportional to the intensity AND THATS IT :-|||||||. I think amplitude squared is light intensity though

Joseph Lee

ionization energy is simply how much energy it will take to remove an electron from an atom. Most of the time, in the cases of non-metals, it will be harder to take away an electron, mostly because they will try to gain one to fill their valence shells. This is all except for oxygen, between Nitroge...

Joseph Lee

the only other degenerate ion would be He+ and that is because there is similarly only one electron in that atom, while still in the level one shell

Joseph Lee

Don't worry too much, we'll all probably be notified in the near future through email! Or you can just ask your TA in the discussion if he hasn't posted it by then

Joseph Lee

Hey! just use the equation frequency = R((1/nfinal^2)-(1/ninitial^2)), and remember, frequency is speed of light/wavelength!

Joseph Lee

I also agree with what everyone's saying, I would also just add that if you need any of these constants, or just need somewhere to find them, I would use the constants equation sheet that they gave us. it is all on there!

Joseph Lee

I believe the correct answer to the question is UV-A light, because longer wavelength is less energy. The smaller the wavelengths get in the EM spectrum, the more dangerous and hazardous they are to organic things because of their higher ionization energy. This means that a longer wavelength (UV-A) ...

Joseph Lee

Yeah, you would want to divide Avogadro's number!

Joseph Lee

It's just different based upon whether you're using the equation with c/lambda, or if you are setting it simply equal to lambda, because if you divide the 3.289e-15 constant by the speed of light, you should find the other constant value!

Joseph Lee

Yeah, agreeing with everyone else, you would find the value of E_5 and E_2 separately with the same equation, and then you would be able to subtract E_5 from E_2 and it would give you the answer!

Joseph Lee

Kinda, the reason why it says to treat it as a particle is so that you divide the mass of the diatomic hydrogen by avogadro's number to find the final mass of ONE particle. Then you just have to make sure to convert that number into kg from g, and then you can plug it into lambda=h/(mv). Hope this h...

Joseph Lee

I don't know if this actually clarifies anything because I'm probably in the same boat as you are, but wouldn't representing energy graphically be the same, just with two variables? Instead of sketching only wavelength and frequency, you would represent them interacting with each other, which is wha...

Joseph Lee

Also! I don't know if anyone posted this already but make sure you remember that because of the equation E=hv, wavelength is INVERSELY proportional to the energy. Same with frequency. The longer the wavelength, the smaller the energy and vice versa. This goes the same as with frequency.

Joseph Lee

Hello! Going off of the previous answer, you also should use the equation [c/(lambda)]=[R(1/(n final)^2)-(1/(n initial)^2)]. That was kind of a disgusting equation but I swear it works! Also make sure to convert to the correct units. You should get the answer n=3, if you need further help just let m...

Joseph Lee

This isn't exactly an answer, more of another question.

What do the n values mean when we say they're jumping and dropping certain levels? Like what does n1, n2, n3, n4 actually mean? Or is this unimportant for us to know about?

Thank you!

Joseph Lee

In terms of significant figures, you always want to take into account the smallest amount of significant figures a number will have in an equation. For example, 3.0m x 1.45678m = 4.37034 = 4.4 m^2 Why is this 4.4m^2 instead of 4.37034m or 4.37 m ? Looking at the 3.0, we can see there are 2 signific...

Joseph Lee

Hi Ashley! It feels so surreal actually typing this out, knowing that you might respond, while also believing that it could just get lost in the sea of all the other thirsty pre-meds who similarly (and shamelessly) need any help they can get. It seems so daunting and hard all the time, how do you c...

Joseph Lee

I have been in this class for a few days now but I thought it would be cool to write a letter of appreciation at the beginning, and then redo it for my final community post as well. To be quite frank, I thought the class would be so difficult to get to know someone's teaching style and personality, ...

Joseph Lee

I'm a little lost on how this works, can someone explain how enrollment works in "non-orientation" style. Also, is it an acceptable thing to do 14b and 7a at the same time along with 30b and a cluster? Just wondering, thanks!

Joseph Lee

Hi Ashley! It feels so surreal actually typing this out, knowing that you might respond, while also believing that it could just get lost in the sea of all the other thirsty pre-meds who similarly (and shamelessly) need any help they can get. It seems so daunting and hard all the time, how do you co...

Joseph Lee

OK THIS IS GONNNA BE GOOD (I saw it on Reddit somewhere long time ago)

A photon walks into a hotel and the front desk manager asks it, "do you need any assistance with your luggage?"

the photon responds, "no, I'm travelling light"

Joseph Lee

Hey All! I'm unsure if someone has said this already, or if this even relates, but a trick I do know in the kitchen is when it comes to preparing... (drumroll) ONIONS! It's incredibly easy to prevent the onslaught of tears, all you have to do is place a wet paper towel on your cutting board while yo...

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