CHEMISTRY COMMUNITY

Daniel Toscano 1L

k = A exp( -EA/RT )
this shows how it can be changed

Daniel Toscano 1L

according to k = A e^( -EA/RT ), if T increases, k increases and if T decreases, k decreases

Daniel Toscano 1L

We're going to have to wait until he emails us.

Daniel Toscano 1L

Our TAs will eventually email us to tell us what to do.

Daniel Toscano 1L

We are going to have to wait until Lavelle/TA's email us explaining what's going down. Maybe they'll email us the tests back?

Daniel Toscano 1L

I think he will send an email tonight regarding at least lecture tomorrow

Daniel Toscano 1L

I think we could use either, but Pt(s) is more commonly used

Daniel Toscano 1L

the anode, which in this case would be Au(s) as it is a solid conductor, should be on the left while its aqueous form, Au 3+(aq), should be on the inside.
The correct order is Au(s)|Au3+(aq)||

Daniel Toscano 1L

I think it's the anode because it is being oxidized from Cu (s) to Cu2+ (aq), and the anode is always oxidized.

Daniel Toscano 1L

Pt or another inert conducting metal solid is used when there is not an inert conducting metal solid in the equation.

Daniel Toscano 1L

The moles (n) refers to the moles of electrons being transferred.
You'll need to balance the half-reactions in order to find the moles of electrons (n).

Daniel Toscano 1L

Yeah, he'll announce soon in lecture

Daniel Toscano 1L

The last part of thermodynamics (the part that was not on the midterm) and electrochemistry

Daniel Toscano 1L

I feel like we would be told if it is an acidic or basic solution.

Daniel Toscano 1L

I think it depends on the UA and what type of session is it (workshop, step-up, drop-in)

Daniel Toscano 1L

the last bit of thermodynamics and electrochemistry

Daniel Toscano 1L

The reducing agent is the substance that causes another substance to be reduced in a redox reaction. The reducing agent itself is then oxidized.

Reducing agent: gets oxidized, causes another agent to be reduced
Oxidizing agent: gets reduced, causes another agent to be oxidized

Daniel Toscano 1L

this website sums up some rules:
https://www.thoughtco.com/rules-for-assigning-oxidation-numbers-607567

Daniel Toscano 1L

Oxidation numbers are related to the charge in that you use the charges to find the oxidation numbers. Primarily, we use known oxidation numbers in a molecule, such as H2O, where we know the oxidation number of O is-2, so each H should be +1, meaning the oxidation number of the molecule will be 0, a...

Daniel Toscano 1L

A galvanic cell is used to produce electricity.
also, a galvanic cell is also known as a voltaic cell.

Daniel Toscano 1L

at top left, go to:
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Daniel Toscano 1L

A charge buildup in the anode solution means that electrons will no longer transfer from anode to cathode. The salt bridge is used to prevent this charge buildup by neutralizing the anode solution.

Daniel Toscano 1L

When a system does work

Daniel Toscano 1L

Well, we know the initial concentrations of N2 and O2, and since we are not told anything about N2O, we assume its initial concentration is zero. N2 and O2 must decrease by some amount, which will become the concentration of N2O at equilibrium. Since the stoichiometric coefficient of N2 is 2 in the ...

Daniel Toscano 1L

Any scientific calculator is fine

Daniel Toscano 1L

I used q=mΔHfus and rearranged to ΔHfus=q/m
but the question says that half of the ice cream melted meaning ΔHfus=q/(0.5m)
And I think enthalpy is usually in kJ/mol, but it depends on what is given in the problem and what is asked for.

Daniel Toscano 1L

">>" means much greater
The entropy of a gas is much greater than the entropy of a liquid, which is greater than the entropy of a solid.

Daniel Toscano 1L

It is a closed system because there will be no exchange of matter, only heat. However, it is not isolated as there can be an exchange of heat.

Daniel Toscano 1L

also, be aware that if it just says "an external pressure of [blank]" then it will be constant

Daniel Toscano 1L

The cutoff is Sunday at 11:59 pm every week I believe.

Daniel Toscano 1L

∆U= (U final-U initial)= change in internal energy

Daniel Toscano 1L

for breaking a bond, the sign of delta H would be positive as energy is required (endothermic). This is because of the fact that bonds don't break spontaneously, so in order to break it energy is required

Daniel Toscano 1L

the universe is just getting infinitely more disordered as time goes by

Daniel Toscano 1L

I think we'll receive it in our next discussion session. That's how it worked last quarter in 14A with Lavelle at least.

Daniel Toscano 1L

When work is done on a system, it is positive. When work is done by a system, it is negative

Daniel Toscano 1L

Also, make sure to include the sign unless specified not to.

Daniel Toscano 1L

collisions are ignored and treated as elastic.

Daniel Toscano 1L

The only real difference is that qp occurs under constant pressure and qv occurs under constant volume.

Daniel Toscano 1L

I'd say use J unless kJ is asked for. It also might depend on the sig figs of the final answer.

Daniel Toscano 1L

I believe smaller than 10^-3

Daniel Toscano 1L

Do the homework problems assigned to us so far for chemical equilibrium and acid-base equilibrium. This is what the test will cover.

Daniel Toscano 1L

look at the posts you made and count the posts made in January 2020, which are your post so far this quarter

Daniel Toscano 1L

I agree with the last user's post in that it is best to round to the number of given sig figs at the very end. When dealing with pH however, the sig figs are typically calculated differently (calculated in the way of a logarithm) which I believe is 3 sig figs usually. For pH, the sig figs in the gi...

Daniel Toscano 1L

no, only what we covered in chemical equilibrium and acids and bases

Daniel Toscano 1L

do problems from the textbook to help prepare. Chemical equilibrium and acids and bases are what will be on the test.

Daniel Toscano 1L

Another way to see it is that Ka+Kb=Kw, which is 14. If ka increases, then Kb must decrease in order to be equal to 14. If Kb increases, then Ka must decrease in order to be equal to 14.

Daniel Toscano 1L

I think it depends on what is given.

Daniel Toscano 1L

Yes you can. ICE tables are really useful for chemistry in general.

Daniel Toscano 1L

Just make sure you post 5 times per week. Those posts can consist of questions asked and/or replies to other people's questions.

Daniel Toscano 1L

I'd like to add on that the equilibrium constant for Cl2 is smaller than the equilibrium constant of F2, meaning the reactant is more favored in the Cl2 chemical equation.

Daniel Toscano 1L

if you are still having trouble understanding, I would recommend looking at the 4th module on the 14B webstie (Chemical Equilibrium Part 3 Video Module) or youtube.

Daniel Toscano 1L

I don't think it matters, just as long it is in accordance with the balanced chemical equation.

Daniel Toscano 1L

We only include gases (g) and aqueous (aq) substances in calculating equilibrium constants.

Daniel Toscano 1L

Q is just ratio of the products and reactants when not in equilibrium, but is calculated the same way as K.

Daniel Toscano 1L

We only omit compounds when they are explicitly liquid or solid. Everything else we include in calculating K and Q.

Daniel Toscano 1L

cis means the same ligands are on the same side while trans means the same ligands are across from each other, separated by the central atom.
The terms tell us about the compound's geometry

Daniel Toscano 1L

Amphoteric means that a molecule can act as either an acid or a base. Amphiprotic describes a molecule that can donate or accept a proton. Water is a good example of an amphoteric molecule that is also amphiprotic. Also, although an amphiprotic molecule is always amphoteric, an amphoteric molecule i...

Daniel Toscano 1L

to add on, be aware of polydentate ligands bonded to the metal as they also contribute to the coordination number. For example, if a metal is only bonded to 1 bidentate ligand than the coordination number would be 2 as the ligand is bonded to the metal 2 times

Daniel Toscano 1L

To add on, at some point, LDF can be stronger than some other intermolecular forces if the molecules is large

Daniel Toscano 1L

We won't be using ICE table until 14B.

Daniel Toscano 1L

Either one is acceptable.

Daniel Toscano 1L

I don't think so as I don't recall Prof. Lavelle going over it in lecture

Daniel Toscano 1L

Finish up new material wednesday, review friday

Daniel Toscano 1L

You can try asking people who have taken the class before and see if they have any past exams and are generous enough to give them to you.

Daniel Toscano 1L

From a scale of 1-10, with 10 being the most difficult, I'd say this class was a 7.5. It is difficult as I only had a limited background with chem and feels really accelerated, but it is manageable if you seek help (review sessions, UA workshops/step-up, PLF sessions, looking up concepts).

Daniel Toscano 1L

I would assume it would be the same questions for each lecture.

Daniel Toscano 1L

Maybe try doing practice problems in test-like situations under a time constraint so you can be more used to actual test-taking.

Daniel Toscano 1L

There is a test bank at the CPO office in SAC.

Daniel Toscano 1L

There will most likely be several review sessions for the final like the ones that we had for the midterm. Lavelle said they were still working on reserving rooms for it last week, so he'll probably tell us about it this coming week 10.

Daniel Toscano 1L

Bronstad acid and bases have to do with protons, while Lewis acids and bases have to do with electrons

Daniel Toscano 1L

-ido and -o mean the same thing, it's just that -ido is now the "correct" version to use

Daniel Toscano 1L

If you have discussion this week, then this week. If not, then next week most likely.

Daniel Toscano 1L

The next time we see our TA's I believe

Daniel Toscano 1L

A bronsted acid donates a proton
A lewis acid accepts an electron pair
A bronsted base accepts a proton
A lewis base donates an electron pair

Daniel Toscano 1L

We won't be posting any more video modules, unfortunately. If you need more help understanding the topic, step-ups and UA workshops are your best bet

Daniel Toscano 1L

My guess is that the TA's will give back test 2 next time we see them

Daniel Toscano 1L

I think generally for small molecules, hydrogen bonds are the strongest, then dipole-dipole, and London dispersion forces as the weakest. However, as the size of the molecule increases, London dispersion forces can dominate over other forces. I'm not sure if ion-dipole forces are considered an inter...

Daniel Toscano 1L

You always want to choose the most stable resonance structure, which in this case would be the first lewis structure.

Daniel Toscano 1L

I think only intermolecular forces affect melting/boiling points.

Daniel Toscano 1L

Polarizing power increases going up and to the right on the periodic table
Polarizability increases going down and to the left on the periodic table

Daniel Toscano 1L

I think a double bond will make the molecule more polar, say in C=O compared to C—O, as the C=O has a π bond. But for NO3-, the resonance hybrid structure would have it's partial charges cancel out, resulting in a nonpolar molecule.

Daniel Toscano 1L

I think it'll be everything after the midterm up until this Friday.

Daniel Toscano 1L

If the element is in the 3rd row or under in the periodic table, then it can have an expanded octet as the third row has access to the d-block, which can hold ten more electrons if needed.

Daniel Toscano 1L

It'll be most safe to write out every resonance structure

Daniel Toscano 1L

Can confirm, 5 times a week

Daniel Toscano 1L

There are several equations you can use.
The one Lavelle showed us was: formal charge=valence electrons of atom-(lone pairs electrons +shared electrons/2) or FC=Ve-(L+S/2)
I personally like using: formal charge=valence electrons of atom-(bonds + dots) or FC=Ve-(B+D)

Daniel Toscano 1L

You're right. I see it as an atom with a small atomic radius holds its electrons more closely and is more willing to take electrons from others, while an atom with a large atomic radius holds its electrons more loosely, so its easier to take an electron away from it. Also, keep the periodic trends o...

Daniel Toscano 1L

I remember Lavelle saying that we only need to know the s-block, p-block, and the first row of the d-block (3d).

Daniel Toscano 1L

c= λv and E=hv apply to light (photons). I think De Broglie's (λ=h/(mv)) applies to particles (electrons), as do Heisenberg's and Schrodinger's equations.

Daniel Toscano 1L

I think the ones already posted are the only ones that are going to be posted.

Daniel Toscano 1L

I think these 2 are the only ones we need to know for Chem 14A.

Daniel Toscano 1L

We will get an equation sheet with a list of conversions we need with the test, as well as a periodic table, so you don't really have to memorize them.

Daniel Toscano 1L

Wesley explained it very well. Then, once you have the mass percentage of each element, you can do the rest of the problem normally.

Daniel Toscano 1L

I'd assume It wouldn't matter whether you did the problems with pen or pencil.

Daniel Toscano 1L

I don't think so. They are not in the objectives listed in Outline 1: Review of Chemical & Physical Principles. I have a feeling it'll be more like the first 4 learning modules we did.

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