CHEMISTRY COMMUNITY

Emil Velasco 1H

I agree I think we just have to wait for more information, but I assume it will still be 3 hours.

Emil Velasco 1H

For this problem, when it asks for one sixteenth or one fourth, we change the numerator (e.g. to 16/[A]o).
What's the math behind this?

Emil Velasco 1H

I think we need to know about rust for the corrosion section

Emil Velasco 1H

The cell diagram always has the anode on the left and the cathode to the right to demonstrate this, so the electrons would move from the anode to the cathode

Emil Velasco 1H

I think we just need to know the half reaction for rust.

Emil Velasco 1H

Both the oxidation and reduction half reaction would have the same number of electrons transferred between them, so this would be your n.

Emil Velasco 1H

Look for the number of electrons being transferred between the half reactions

Emil Velasco 1H

cathode is where reduction occurs and the anode is where oxidation occurs

In a cell diagram, the anode is on the left side while the cathode is on the right.

Emil Velasco 1H

For each reaction that is spontaneous under standard conditions (that is, K . 1), write a cell diagram, determine the standard cell potential, and calculate deltaG for the reaction: (a) 2NO32(aq)18H1(aq)16Hg(l)S ~~For the cell diagram, why would the right side only be balanced with Platinum vs the l...

Emil Velasco 1H

w refers to the number of possible states/possible orientations

Emil Velasco 1H

Gibbs Free Energy being at zero signals that the reaction is at equilibrium

Emil Velasco 1H

My TA said that something like this equation was just a way of mathematically showing that heating an endothermic reaction favors products vs heating an exothermic favors reactants

Emil Velasco 1H

Electrons flow from the anode to cathode usually so I don't think there's an exception

Emil Velasco 1H

Positive voltage = spontaneous reaction
Negative voltage = nonspontaneous reaction

Emil Velasco 1H

My TA mentioned how oxidation is related to the anode because both started with vowels while the cathode is with reduction because both started with consonants.

Emil Velasco 1H

5 posts constitute one week

Emil Velasco 1H

Van't Hoff allows us to find K at different temperatures from Gibb's since K changes when the temperature does

Emil Velasco 1H

Gaining electrons is reduction (going for negative) and losing electrons is oxidation (going for positive)

Emil Velasco 1H

Spotaneity is determined by both as presented in the chart above, but either could be used in order to see whether a reaction is spontaneous or not

Emil Velasco 1H

You can find the units used on the equation sheet

Just look for what units the problem gives you and what you are trying to get. Using R with the right units allows you to cancel out the things you don't need in order to get what you want

Emil Velasco 1H

It's also important to note that reversible does the most amount of work.

Emil Velasco 1H

Irreversible uses w=-Pex * deltaV

Reversible uses w=-nRTln(V2/V1) (Does the most work)

Usually the problem will be explicit in whether a reaction is reversible or irreversible

Emil Velasco 1H

For isothermal, there is no change in temperature therefore there is no change in internal energy

Emil Velasco 1H

Cv is constant volume and Cp is constant pressure

Emil Velasco 1H

I don't think the midterm itself is curved

Emil Velasco 1H

Delta H stands for Change in Enthalpy

H - Enthalpy
Delta - Change in

Emil Velasco 1H

Choosing which R to use depends on what units you are trying to cancel out in order to solve for your specific answer.

Emil Velasco 1H

Most of these variables will be given in the question in order to solve.

There was also a list put up with some useful terms that describe whether some things are constant, like "isothermal" for constant temperature or "isochoric" for constant volume.

Emil Velasco 1H

I think for all intents and purposes they represent the same idea.

Emil Velasco 1H

Thank you!

I think we will need to know these terms for the test in order to interpret problems

Emil Velasco 1H

Do they represent the same value or no?

I looked some stuff up and what I've seen has varied

Emil Velasco 1H

When you convert a gas to mols, they said you turn it from Liters to Mols through the conversion factor of:

1mol/22.4

but I'm not entirely certain if this is accurate or not

Emil Velasco 1H

pKa + pKa = Kw (autoprotolysis constant) = 14

This equation can be flipped around respectively to find a value you need.

Emil Velasco 1H

Le Chatelier's Principle applies whenever a system is "disturbed" in the sense that reactants or products are added/removed.

Emil Velasco 1H

Increasing and decreasing temperature changes the value of K because it acts as either a product or reactant (exothermic or endothermic respectively)

Emil Velasco 1H

Adding heat to an exothermic reaction favors reactants because heat is a product, so thereby increasing the product, it favors the formation of reactants

Emil Velasco 1H

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it.

Emil Velasco 1H

Only include (aq) and (g) in your equilibrium, as solids and liquids/solvents like H2O are not.

Emil Velasco 1H

I always use Khan academy

Emil Velasco 1H

K the point of equilibrium while Q is a reaction quotient by which the reaction is not at equilibrium yet

The value of Q relative to K can give you clues towards which way the reaction is going

Emil Velasco 1H

I think it's just a given concept but not necessarily set in stone for identification purposes

Emil Velasco 1H

You use Kp unless it specifically asks for Kc

Emil Velasco 1H

I believe Kc deals with Equilibrium Constant concentrations while Kp deals with Equilibrium Constant partial pressures

Emil Velasco 1H

Tanmay Singhal 1H wrote:I'm confused on why water isn't counted in the K/Q equation.

Water is not counted because water is a liquid

Solids and liquids are not included in the equilibrium constant expressions (K=P/R)

Emil Velasco 1H

When Q=K, then the reaction is at equilibrium

Emil Velasco 1H

K = Kc = Kp

They are just different notations for whatever phase your equation is dealing with (e.g. gas w/ pressure)

Similarly, K = Q = Qc = Qp

Emil Velasco 1H

If Q does not equal K or vice versa, then I believe you would have to solve for either respectively. If Q is the same value calculated, then the reaction is at equilibrium

Emil Velasco 1H

The ideal gas law assumes that conditions of measurement are perfect, but in the experimental sense, they aren't.

Emil Velasco 1H

While liquids do not have a defined concentration (molarity), aqueous solutions do.

Emil Velasco 1H

Both work as their respective units of measurement, mostly dealing with gasses and pressure

Emil Velasco 1H

R is the gas constant, should be found on the equations sheet

Emil Velasco 1H

Maddie wrote:Will he give us the actual electronegativity values on the tests though?

We won't be getting electronegativity values, so we have to know the trend on the periodic table.

Emil Velasco 1H

Anokhi Patel 4G wrote:what exactly is london dispersion?

London dispersion is another name for Van der Waals forces, which is essentially really weak and temporary polarizations occurring due to the random movement of electrons in a molecule. It is the weakest intermolecular force and may occur on all molecules.

Emil Velasco 1H

Having a triple bond in CO fulfills the octet rule for Carbon has Carbon would want to have an octet.

Satisfying the octet rule precedes Formal charges

Emil Velasco 1H

Intermolecular strengths are: Ion-dipole, H-bond, Dipole-Dipole, Ion-induced dipole, Dipole-induced dipole, and London Forces

Emil Velasco 1H

Elements after the 3rd period may have expanded octets due to their access to the 3d subshell.

Emil Velasco 1H

Doesn't matter where you start as long as the overall FC of the molecule matches what is given or is at the most favorable FC which is 0.

Emil Velasco 1H

You try to make the formal charge 0 where possible as long as the octet rule is satisfied. If not, you aim for the lowest energy structure possible that satisfies the octet rule, which involves having the lowest number of formal charges, especially with the central atom.

Emil Velasco 1H

Usually any element under the 3rd period may have an expanded octet due to having the whole of the d-block possible in their electron configuration

Emil Velasco 1H

Resonance structures essentially combine into a resonance hybrid. Each resonance structure describes how possible delocalized electrons may form bonds.

Emil Velasco 1H

When you draw Lewis structures, you just try to get the lowest energy structure possible, typically with a 0 formal charge where possible. If not, I think you just make the entire charge of the atom match what is given.

Emil Velasco 1H

These four elements C, N, O, F follow the Octet guideline as they do not have access to the expanded octets found with the d block

Emil Velasco 1H

I think you use De Broglie's for any time you are given any values toward the variables for conversions between them.

Emil Velasco 1H

Once 4s is filled, it has a higher energy than the 3d orbital, so the electrons removed are from 4s, the outermost shell.

Emil Velasco 1H

I think we just need to know how the concept relates to whatever question is being asked as opposed to actually naming them.

Emil Velasco 1H

Flourine has the highest ionization energy, as it requires the most energy in order to lose an electron.

I believe Noble gases are excluded in this case but I'm not too sure.

Emil Velasco 1H

"Degenerate" is just a term used to describe the spdf orbitals having the same energy; This applies to a single-electron atom like Hydrogen.

I'm not sure if this was mentioned in lecture but I know for sure that it was mentioned at a review session

Emil Velasco 1H

Khan Academy and the module were extremely helpful in understanding the topic!

Emil Velasco 1H

Khan Academy's article was really helpful in explaining the building-up principle.

Emil Velasco 1H

I don't think we have to know the actual equation but rather just the general trend of Ionization Energy in the periodic table.

Emil Velasco 1H

For part c, when n=2, it has 2s and 2p are valid orbitals

in which 2s contains 1 subshell orbital (mL=0) and 2p contains 3 subshell orbitals (mL=-1,0,+1)

Emil Velasco 1H

E = hv is used to solve for the energy of an electron.

Sometimes you are not given v (frequency) therefore you must use c = λν, substituting the v in E=hv for v = c/ λ:

so E = hc/ λ

Emil Velasco 1H

The speed of light is constant at 2.998x10^8 m.s^-1

Emil Velasco 1H

h is Planck's constant but h-bar is h/2pi

Emil Velasco 1H

n levels are just the levels of energy for an electron in which n is a quantum number (n=1,2,3, etc.). When electrons increase in energy, the n increases.

Emil Velasco 1H

I think all the equations are given to us, but we just have to know when to use them.

Emil Velasco 1H

Photons do not have mass, only momentum.

Emil Velasco 1H

We use 10 for delta V

Emil Velasco 1H

I used 5.00 value for delta v

Edit: Do not use 5.00 value for delta V:

Lavelle addressed this in his solution manual so we use 10 as delta v
https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf

Emil Velasco 1H

I think we get an equation sheet

Emil Velasco 1H

Helps a lot to memorize when you're doing practice problems but if you forget, there's always a cheat sheet he puts on the test for us to look at with all the constants!

Emil Velasco 1H

Studying chem has shown me a lot of funny jokes

He He He

Emil Velasco 1H

I'm also really rusty but so far I think doing the practice problems he has on his Course Outlines (from the 14A website) have been extremely helpful in getting exposed to practice problems. His modules have also helped me a ton in understanding some things I haven't touched up on since 4 years ago!

Emil Velasco 1H

I think there's a limit to how far an atom can be from the nucleus before it is lost as a "free electron."
I'm honestly not entirely sure though.

Emil Velasco 1H

Online it says that he was able to derive this constant from experimental measurements from black-body radiation.

Emil Velasco 1H

h = Planck's constant (6.626*10^-34 J*s)

It'll be given to us on the front sheet of a test with all the constants, I think

Emil Velasco 1H

The speed of light (3. 10^8 m/s) will always be a constant.

Emil Velasco 1H

The detectors sense that the electrons had shifted to other points as opposed to a single point due to diffraction, which is demonstrated through the electron's wave-like properties.

Emil Velasco 1H

Also I believe wavelike properties are only demonstrated by objects that are extremely small.

While light does exhibit wavelike properties, the equation cannot be applied towards it.

Emil Velasco 1H

My TA said the test would be graded the same day so the grades might be up on ccle?

Emil Velasco 1H

(a) How would you prepare 1.00 L of 0.50 M HNO3 (aq) from “concentrated” (16 M) HNO3 (aq)?

(b) How many milliliters of 0.20 M NaOH(aq) could be neutralized by 100. mL of the diluted solution?

I'm not entirely sure how to begin solving this problem

Emil Velasco 1H

I think you round the answer's sig fig to the smallest number at the calculation

Emil Velasco 1H

Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number. I don't think we need to memorize the number for the test, I think Lavelle mentioned having a front sheet on tests with ...

Emil Velasco 1H

Personally I use two to three decimal places but I feel like in test, we should use all of the decimals for extra accuracy in our calculation

Emil Velasco 1H

Would they ask "How many significant figures are in this number?"

I think I'm just confused about how this would be used practically in a problem?

Emil Velasco 1H

I think we just use the ones called for by the problem

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