CHEMISTRY COMMUNITY

Philip

Would we need to know electrolysis for the final?

Philip

I think the main way we use this equation is to find the new equilibrium constant based on a change in temperature

Philip

I think it's to show that energy is release or loss

Philip

You raise e by both sides of the equation

Philip

Extensive depends on the amount while intensive doesn't. It's important because it tells us which constant or which equation to use like specific heat capacity vs heat capacity, etc.

Philip

It symbolizes the equilibrium constant of the reaction

Philip

Can anyone please explain to me why when it is an isothermal reversible expansion, we can assume that internal energy is 0 and q = -w? Thank you Isothermal means the temperature is constant and so the internal energy doesn't change so the change is 0. If change in internal energy is 0 then 0 = q + ...

Philip

THANK YOU SO MUCH DR. LAVELLE!!!!!!

Philip

I think it is used when there's no solid that was explicitly said in the problem.

Philip

I think he curves up depending on the class average at the end of the quarter

Philip

As well as doubling the mass of the cathode electrode will it increase or decrease the cell potential

Philip

Also, if water is added in the cathode solution would the cell potential increase or decrease?

Philip

A concentration cell was constructed with two electrodes containing ZnSO4 (aq) at 25 degrees C. The cathode concentration is 3.0M and the cell potential 0.0866V/
Calculate the concentration of the anode solution

Is LnQ going to be the anode concentration over cathode or cathode over anode?

Philip

Given that delta H reaction = 161 kJ/mol and K = 8.43 x 10^-12 for the reaction at 25 degrees C. Calculate K at 125 degrees C. Assume that delta H reaction and delta S reaction remain constant over this temperature range.

Idk what I did because somehow I ended up with a new K value of 6.808 x 10^-96

Philip

Van't Hoff Equation is used to calculate the new equilibrium constant based on temperature change

Philip

SeO4 2- (aq) + Au (s) = Au 3+ (aq) + SeO3 2- (aq)

I was confused with the reduction half-reaction
I thought it would be 2e- + SeO4 2- + H+ = SeO3 2- + OH-

Im assuming Im wrong since I put H+ was I supposed to put H2O instead?

Philip

Also what R are we using?

Philip

Do we need to convert RT/nF * lnQ into 0.0592/n log Q?

Because I decided not to convert during one of the problems on the test as I forgot the conversion rate and I got the wrong answer even when I think my calculations were right. So is it necessary to use this conversion?

Philip

2Ag+ (aq, 0.10M) + Cu (s) = 2Ag (s) + Cu 2+ (aq, 0.20M) Standard E cell is 0.460V

Can someone solve this pls.

Philip

Oops the Lithium half-reaction has standard E = -3.040V

Philip

Also I need to find the standard Gibbs Free Energy, do I just use -nFE(standard)?

Philip

The half-reactions are
Ce 4+ (aq) + e- = Ce 3+ (aq) Standard E = 1.44V
Li+ (aq) + e- = Li (s)

How do I know which one is the cathode and which one is the anode for me to use standard E cell = standard E cathode - standard E anode????

Philip

In a cell diagram, do we always use Platinum if nothing else is stated to be used?

Philip

So in a concentration cell, is the anode always the one with the lower concentration?

Philip

This is very beautiful. Thank you so much Lavelle for everything you've done and continue to do for your students :)

Philip

I think it's either/or. If you end up with a C you pass or if you end up with 250 points you pass the class. Last quarter I had 444/500 points and ended with an A- so he does kind of curve but we won't know until they find the average points out of 500 of the class

Philip

Using the stoichiometric ratios and creating an ice table you should be able to calculate the molar concentrations

Philip

Thank you for trying to lighten up the mood

Philip

To stay focus I usually take a couple of breaths and try my best to only think about the task at hand and ignore my surroundings

Philip

His latest update still didn't tell us how we are turning in the final

Philip

Use an ice table and any available information like the pKa or pKb as well as any equilibrium constants would be needed to solve such a problem

Philip

I heard some people's take-home final is taken over a large window of time to accommodate for everyone but the tests are still designed to take the same amount of time. The only difference is to scan and upload our answers I guess. I hope we get an update soon

Philip

How are you guys going to be studying for the final I'm planning to look over the study guide Dr. Lavelle sent out, do the endgame worksheet Lyndon posted, and review my notes/ do practice hw problems. Also some UAs released another set of practice problems! https://lavelle.chem.ucla.edu/forum/view...

Philip

How are you guys going to be studying for the final

Philip

How will we turn in the final??

Philip

His latest email said that it'll be a take-home final now and he'll post the test on the website

Philip

When are the answers going to be posted?

Philip

Are we still going to have a review session on Friday?

Philip

Whenever we balance the half-reactions, how do we know whether we need to add an H+, OH-, and/or H2O on what side of the reduction or oxidation half-reaction?

Philip

So in a concentration cell, is the anode always the one with the lower concentration?

Philip

I'm confused about the relationship between Boltzmann's constant and the gas constant.

Philip

Then explain the graph of pressure vs volume of the reversible and irreversible expansion?

Philip

What is the difference between isothermal reversible expansion vs irreversible expansion?

Philip

How does sig figs factor in calculating K then?

Philip

The total change in entropy is 0 if the system is isothermal and reversible expansion. The entropy change of the surrounding is 0 if the system is isothermal and irreversible expansion.

Philip

We calculate the last step because the change of entropy is a state function and we only care about the initial and final state of the reaction. In this case, we want the entropy change of the water evaporating at 85 degrees so we need the water to heat up and change phase and then bring the temp of...

Philip

One mole of COBr2 was injected in a 1L flask at a certain temperature. The equilibrium mixture was then analyzed and found to contain 0.304 moles of CO.
Calculate the concentration of each species at equilibrium.

Philip

2NO + O2 = 2NO2

Why would decreasing the volume of a system increase the partial pressure of NO2?

Philip

Pressure times Volume = moles of gas times the gas constant times the temperature

Philip

When calculating K, why are there no units

Philip

It would either underline N or O or it'll be written as NO2 or ONO (and the first element is the one that's bonded)

Philip

It is platinate because the compound is an anion

Philip

How can you tell a ligand is a polydentate? And what are examples of anionic ligands, how are they different from anions? A ligand is polydentate if it binds to the metal in two or more places, because it has two or more lone electron pairs. For example EDTA is a polydentate. They are different beca...

Philip

So the name for [Fe(OH)(OH2)5]Cl2 is pentaaquahydroxidoiron(III) chloride. But how did they get the charge on iron? And why is it chloride if there are two chloride, shouldn't it be dichloride? Since there is two chlorine it has a -2 charge so the coordination compound has an overall 2+ charge (Also...

Philip

Only if the metal coordination compound is an anion

Philip

Based on their electronegativity, i believe

Philip

amphoteric metal oxide

Philip

Which would be the stronger acid HClO or HClO2? I know that you first look at bond length and then anion strength but how would you figure this one out?

HClO2 is stronger because of how there's more oxygen and a higher electron pulling ability, which delocalizes the electron

Philip

How do you know if the solution will result in OH or H

Philip

How is the pH of a solution is related to its hydronium ion and hydroxide ion concentrations?

Philip

how can carbon dioxide lead to respiratory acidosis?

Philip

Do we need to know ligand names for the final

Philip

Yep always

Philip

I am confused on how to use Bis, Tris, Tetrakis, Pentakis

Philip

What is chelating?

Philip

It happens with polar molecules with N, O, F, elements that have lone pairs that attract Hydrogen

Philip

What's an oxidation number

Philip

What is a ligand?

Philip

So I was wondering why for T shape the two electron pairs are like right next to each other in the trigonal planar part of the trigonal bipyramidal

Philip

I missed the lecture can someone summarize what hybridization is

Philip

What's a dipole

Philip

So the more electronegative elements are more likely to get the electron?

Philip

Elements like Xenon can have 12 electrons. Is 12 the max or what for elements with octet exceptions.

Philip

Are there other elements that can have 12 electrons like Xenon?

Philip

How come Xenon can have 12 electrons

Philip

Hund's Rule states that each suborbital will be filled with electrons of parallel spins
Pauli's Exclusion Principle states that you can't have the same spin for paired electrons

Philip

Why does oxygen have lower ionization energy compared to nitrogen

Philip

I'm confused about the difference between the two

Philip

What's a dipole?

Philip

What are the octet exceptions?

Philip

I believe it's only for covalent bonds

Philip

Wait I dont understand how a molecule like SO4 has a negative charge or NH4 with a positive charge

Philip

Multiply 60W with 1s to convert it to Joules
Now use the speed of light equation and energy equation to get Energy = planks constant times speed of light over the wavelength. You will get the energy per photons
Then you divide the energy emitted with the energy per photon to get the number of photons

Philip

1.1 Lines in the Balmer series of the hydrogen spectrum are observed at 656.3, 486.1, 434.0, and 410.2 nm. What is the wavelength of the next line in the series?

Philip

You calculate by finding the formal charge, the more atoms with 0 formal charge the better. We also have to consider the electronegativity of the element

Philip

I think it is safe to assume that it will be used in one dimension

Philip

s-block metals have lower ionization energies compared so they tend to form cations since they are more willing to give electrons away, so they are more reactive.

Philip

When do we use this equation for?

Philip

I know how to get the third quantum number but like what does this number tell us about the electron?

Philip

Where did the 4pi come from

Philip

Plancks Constant my guy

Philip

When is Rydberg's equation used?

Philip

Do photons have mass?

Philip

What was the standing wave animation/picture that was shown in class

Philip

How come this wave equation can't be applies to light since light is massless but the equation was derived from the speed of light equation C= wavelength times frequency.

Philip

Whats the length of a bond?

Philip

It should be fine

Philip

To prepare a fertilizer solution, a florist dilutes 1L of 2M NH4NO3 by adding 3L of Water. The florist then adds 100mL of the diluted solution to each plant. How many moles of nitrogen atoms will each plant receive?

Philip

Help balance equation pls

Fe2O3 + CO = Fe3O4 + CO2

and

Fe3O4 + CO = Fe + CO2

Philip

Help cant solve
5g of KMnO4 is dissolved in 150mL. If 20mL of the solution is removed and placed in a 250mL what is the concentration?

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