CHEMISTRY COMMUNITY

Katie Le 3K

q is heat. h is enthalpy

Katie Le 3K

In an endothermic reaction, heat is a reactant. In a exothermic reaction, heat is a product.
Just treat heat as a product or reactant depending on reaction type and apple Le Chatelier's principle.

Katie Le 3K

When Ka value is 10^-5. If you are unsure, always double check using percent ionization. If its above 5% you cant use the shortcut

Katie Le 3K

Yes they are synonymous.

Katie Le 3K

does anyone have good diagrams/images for cp and cv calorimetry? the video recording is too blurry to take a picture and i wasn't sure which ones online would be good.

Katie Le 3K

Yes you can use it w both equations.

Katie Le 3K

Water can donate either a proton or accept a proton!

Katie Le 3K

There will be a higher conc of hydronium ions in acidic solutions.

Katie Le 3K

It stays the same because all of the energy is being used to break bonds and not used for kinetic energy.

Katie Le 3K

The steam would burn at 100 C compared to water at 100 C because steam has more energy than water at 100C. That energy transfer from the steam to hand releases heat.

Katie Le 3K

There are no exceptions to this rule

Katie Le 3K

Total pressures is the sum of all partial pressures in rxn.

Katie Le 3K

A better way to remember is that K changes w/ temperature.

Katie Le 3K

In today's lecture, Dr. Lavelle says that if [H3O+] < 10^-7 its neutral because of autoprotolysis.

what is autoprotolysis

Katie Le 3K

They are all K constants meaning they calculate the same thing (equilibrium constant)
the subscripts denote the type of equilibrium constant it calculates.
Ka, Kb, Kw, Kc, and Kp are K of acid, base, dissociation constant of water, concentration, and partial pressure respectively.

Katie Le 3K

Based on if the rxn is endo or exothermic, we can use temperature to find which side the rxn favors

Katie Le 3K

same thing!

Katie Le 3K

You use the ICE chart. If you click feedback, Sapling should provide one for you.

Katie Le 3K

H2O in liquid form is not included along w/ solids.

Katie Le 3K

You would normally be given the concentrations or pressures. If you are given concentrations, its Kc. If you are given partial pressures, its Kp

Katie Le 3K

Yes. It only slightly favors it. you cannot make a strong statement about the favor unless its greater than 10^3

Katie Le 3K

Both are calculated the same way. Kc uses concentration Kp uses pressure.

Katie Le 3K

Cumulative w focus on topics we spend longer time on.

Katie Le 3K

1 mmole = .001 mole

Katie Le 3K

some ta's review it in office hours or you have to email them to set up a specific appointment

Katie Le 3K

Read the textbook and do the problems assigned in the outlines. ALso, going to the UA sessions are really really helpful. I feel like they explain concepts really well

Katie Le 3K

The charge outside the bracket (2-) represents the overall charge of the molecule. Thus, the charges of the atoms inside the brackets should total up to 2-

Katie Le 3K

will the final have partial credit like midterm 1?

Katie Le 3K

In lecture he called this pentaammine - chloro - cobalt (II) chloride dihydrate

I'm confused on the chloride and dihydrate outside of the ligand brackets.

Why is Cl chloride and not chloro and why is 2h2o dihydrate instead of diaqua?

Katie Le 3K

I like them a lot. I feel like I solidify my understanding of the Lavelle's lecture and you can ask them questions. They also give you practice problems that are very helpful imo. Highly rec going to Hannah's or Justin's sessions.

Katie Le 3K

Its everything we have learned (cumulative)

Katie Le 3K

Thank you so much!

Katie Le 3K

there shouldnt be any time conflicts with chem14b lecture

Katie Le 3K

O2 is in excess for combustion problems. i think its just something we assume unless explicitly stated otherwise

Katie Le 3K

In terms of application, de broglie can be used on any object as it has mass as a variable. Whereas e=hv is for energy of a photon.

Katie Le 3K

Isoelectronic means that two things have the same amount of electrons. An example would be that Ag 3+ and Mg 2+ are isoelectronic.

Katie Le 3K

Yea, i think its the myucla date because our final is going to be longer than our midterms so i dont think it'll fit into our 50 min discussion sessions

Katie Le 3K

i do some low impact hiit workouts from youtube when im watching tv. paula b has some really good ones. they're not too hard but it helps when you've been sitting at your desk the whole day :)))

Katie Le 3K

i watch youtube or play video games :)))

Katie Le 3K

A helpful way is it draw out the lewis structures of the molecules and see which one has lone pair electrons. The one with lone pair electrons is the Lewis base.

Katie Le 3K

To know which one gives the most contribution, you have to look at the formal charges. the lewis structures with atoms whose formal charge is 0 or close to 0 are the most contributing

Katie Le 3K

You'd look to see if the formal charge of the molecule would be 0 because it's more stable/more likely to happen.

Katie Le 3K

Its basically just an unpaired electron so it'd look like a dot next to the element.

Katie Le 3K

It's like an extra step to verify you drew it correctly. Like if it was Na-, if your total charge ended up being -1 that'd be good.

Katie Le 3K

no! you should be able to determine the difference in electronegativity between them though.

Katie Le 3K

Hi, a lewis acid will accepts electrons while a lewis base will donates these electrons. the way i figure out is making lewis structures for the two molecules and comparing which one would be receiving an electron and which one gives an electron. as a general tip, molecules with +1,+2,+3, or any + m...

Katie Le 3K

The negative and positive refers to the charge. You can find it out by finding the formal charge of each element and just adding them all together.

Katie Le 3K

I also feel that way for some of my midterms but I think we can make it up during the next two finals!!!

Katie Le 3K

I think if not asked for it directly in the question, it's safe to assume its at equilibrium.

Katie Le 3K

Orbitals are math functions that describe the position of an electron using the quantum numbers.

Katie Le 3K

Yea the group number corresponds with the number of valence electrons.

Katie Le 3K

How come the hydrogen in CH20 doesn't have 8 filled valence electrons like C and O

Katie Le 3K

sorry if this is dumb but in Prof Lavelle's lecture, he was drawing a picture of the Lewis structure of Cl and said " we know that cl has 7 valence electrons" and then drew dots. but like how do i find out the valence electrons of cl? am i supposed to memorize it?

Katie Le 3K

The 4s shell has less energy than 3d so electrons fill the lesser energy shell first.

Katie Le 3K

De broglie wavelength is used when you have a mass and velocity. Whereas the other wavlength equations deal w frequency.

Katie Le 3K

No.Gamma rays have the shortest wavelength. Wavelength and frequency are inversely proportional. When wavelength decreases, frequency increases which also increases energy.

TLDR
Long wavelengths = shorter frequency = less energy
Short wavelengths = longer frequency = more energy

Katie Le 3K

In Prof. Lavelle's lecture, he writes

N, Z=7 1s^2 2s^2 2px^1 2py^1 2pz^1

I understand that its 2p^3 but how do I figure out the different px py pz?

Katie Le 3K

P is momentum. On our formula sheet, it says p = (mass)(velocity)

Katie Le 3K

On our formula sheet, if you look closely, the italicized v is frequency and the normal v is velocity.

Katie Le 3K

Yes Lyman ends with n=1. Balmer ends with n=2

Katie Le 3K

Yes you're correct. It's easier if you take notice of what units you need to get your answer.

Katie Le 3K

If the energy of a photon doesn't "match with" (less than) the work function, it just passes through the metal.

Katie Le 3K

Debroglie equation: wavelength = constant/(mass)(velocity)

Does the equation have a set unit like it always has to be in kg? and does velocity always have to be m.s^-1

Katie Le 3K

depending on the problem, itd be given to you or you have to find out. youre best bet would be to understand coneptually what the threshold means so that when a question asks you about it without outright telling you you'd know. also, threshold is not constant it depends on what substance it is

Katie Le 3K

Lyman is uv light and the energy level is 1 while balmer is visible light and the energy level is 2

Katie Le 3K

quanta is used to describe small units that are discrete so photon is quanta

Katie Le 3K

Yes in terms of the wave model amplitude is related to intensity of light and number of photons

Katie Le 3K

Intensity is in simpler terms the number of photons in light. so increasing intensity means adding more photons

Katie Le 3K

I keep a lot of decimals in my equation answers and only round at the end of your multistep equation.

Katie Le 3K

You can look up a diagram called "Stoichiometry Island" on Google and it will help you figure out what formulas/constants you need to use to find your answer. Avogadro's # is used when you want to go from moles to atoms or molecules and vice versa.

Katie Le 3K

I think he was saying that those processes have similar reactions. For example, I believe they all involve O2 as a reactants and CO2 and H2O as the product.

Katie Le 3K

Molarity = moles/volume. Does 'v' have to be in liters or can it be in other units like ml?

Katie Le 3K

I use sig figs at the end of a multistep equation. I think it's supposed to help with the accuracy of your final answer.

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