CHEMISTRY COMMUNITY

Julia Lee

Do you guys know what he said he's gonna call his review sheet?

Julia Lee

Does anyone know how to solve the very last question (labeled Question #1) on Yekan's slides for week 8? It's the one on half life but idk what equation he used to solve for the number of days.

Julia Lee

Does anyone know if Karen posted worksheet 9 yet?

Julia Lee

If something has a positive cell potential, it is likely to be reduced. If it has a negative cell potential, it is likely to be oxidized.

Julia Lee

If an element is a good reducing agent, it has a high reducing power. This means that it is what is getting oxidized in a reaction, which also means it has a low (negative) E value. The opposite is true for oxidation.

Julia Lee

I'm pretty sure you leave it out.

Julia Lee

Can someone please explain #4 on the electrochem worksheet? I don't understand why the answer is Ag+ not Fe2+

Julia Lee

On quiz 3 do we have to know just Galvanic/Voltaic cells or electrolytic cells as well?

Julia Lee

Yes, especially know that max work = change in G = -nFE
I believe Professor Lavelle went over this in lecture Friday as well.

Julia Lee

if the two ions in the cathode portion are both aqueous, why do we separate them with a comma rather than a solid line when writing the cell diagram?

Julia Lee

So, just to clarify, if there is not solid in the cathode portion of the cell diagram, we have to add Platinum to it? Can anyone explain why we must do this?

Julia Lee

Does anyone know if it matters whether to use H+ vs H3O+ when writing redox reactions?
I think in the textbook it says to write H+ instead.

Julia Lee

Does anyone know why the solutions manual assumes the temperature is 298K (roomtemp) for the Gibbs Free Energy calculations even if we are not specifically told in the problem?

Julia Lee

So is there no worksheet for this week?

Julia Lee

Yea, I don't think he's finished making it yet. It will probably be posted this weeked.

Julia Lee

In a Reversible process, the pressure is not constant (but Temp is constant). For reversible processes use the equation w= -nRTln(V2/V1). In an irreversible process, the pressure is constant and thus the temperature changes. For irreversible processes, use the equation w= -P(change V). In a reversib...

Julia Lee

Most of the time, they are provided on the constants and equations sheet. You can check the sheet on his website to see if it is on there. Usually the one on his website reflects what is given to us during the tests & midterms.

Julia Lee

Wait, did Lavelle go over isometric in class? I only recall hearing about isothermal

Julia Lee

"enthalpy (H), is the sum of the internal energy of the system plus the product of the pressure of the gas in the system times the volume of the system."

Julia Lee

Does anyone know what a path function is? Is it just the opposite of a state function?

Julia Lee

Wait so what are extrinsic and intrinsic properties than? Are how are they different than extensive and intensive properties?

Julia Lee

Can someone explain to me what qp is? Professor Lavelle was going over it in lecture but I'm still a little confused.

Julia Lee

Yea, I'm pretty sure that in lecture he said that something dying means that it goes to equilibrium.

Julia Lee

Hey,

Do any of you guys know whether we should use bar or atm when calculating the partial pressures of gases?
My TA said to always convert to bars but a UA said that Lavelle prefers atm.

Julia Lee

Make sure to know Le Chatelier's principle and how a reactions reacts in response to a change in pressure/volume, concentration, temperature, etc

Julia Lee

Yes, the volume would just be a constant.

Julia Lee

thanks! That helps a lot :)

Julia Lee

Can someone please explain to me how number 4 part d and number 5 are solved for the the Chemical Equilibrium worksheet?

Julia Lee

Hi guys,

Does anyone know whether polyprotic acids and bases will be on this upcoming exam because the last couple of homework problems involve polyprotic acids and bases but we haven't covered it in class yet.

Julia Lee

This is what Professor Lavelle posted previously on this topic: "When K is smaller than 10-3 then X is much smaller than the initial concentration, [I], and therefore: [I] - X is approximately equal to [I]. Note: X is not zero. But X is much smaller than [I] and therefore the difference is appr...

Julia Lee

Ka times Kb= Kw = (10^-14)
pKa +pKb = 14

Julia Lee

As someone new to Lavelle I would like to ask, how well do the lectures prepare us for the midterm and final ? Is watching the modules absolutely necessary to ace this class or do the lectures go over all the topics well enough ? Also, how rigorous are the tests (not the final and the midterm the o...

Julia Lee

Rachel Yoo 1F wrote:Kp is for partial pressure with units like atm, bar, torr, etc. Kc is for concentrations and will have mol/L for units

Do you know how we would convert between these different units for partial pressure or if it would be necessary?

Julia Lee

Since Kc uses concentrations which are approximations, I know that we do not include mol/L units in our calculations. For Kp and partial pressures, do we leave out the units as well? Yes, I believe you can leave out units for both. Although when doing calculations using Partial Pressures, it may be...

Julia Lee

Would anyone be able to inform me of what we covered in lecture today 11/14? I wasn't able to make it. Thanks in advance! Yea, we covered Acids and Bases Equilibria in lecture today. We reviewed basics on acids and bases from last quarter and then we learned about the Autoprotolysis constant (Kw). ...

Julia Lee

Resonance stabilizes anions by delocalizing their negative charge. By creating a more stable resulting anion, the relative acidity will increase. Dr. Lavelle stated during lecture that the two things that make an acid a strong acid is: 1. the acid loses H+ easily and 2. the resulting anion must be s...

Julia Lee

Professor Lavelle went over in lecture that Alkali metals(group 1) oxides and hydroxides as well as Alkali Earth metal(group 2) oxides and hydroxides will be strong bases. Some examples he gave of these were Li2O, NaOH, Na2O, KOH, CaO, Ca(OH)2, Mg(OH)2. A lot of strong acids have an element from the...

Julia Lee

Yes, that is correct.

Julia Lee

When do we use bis-, tris- etc. vs di- tri-, etc? You use bis-, tris-, tetrakis-, pentakis-, etc when the name of the ligand already has a di-, tri-, tetra- inside of it. For example, ethylenediamine already has di inside of the name, so you would say bisethylenediamine, rather than diethylenediami...

Julia Lee

Nitro is NO2 (nitrogen linked to metal) while nitrito is ONO (oxygen is linked to metal)

Julia Lee

When does the roman numeral come into play, basically how do you determine what roman numeral to place on a compound? The roman numeral is used to state the oxidation state of the transition metal. It can be figured out by using all the other charges in the coordination compound since you know the ...

Julia Lee

No, I don't think so.

Julia Lee

So, for example, if a molecule is sp^2 hybridized, than its hybridization will have 3 degenerate sp^2 hybridized orbitals and one leftover unhybridized 2p orbital. This unhybridized p orbital will account for pi bonds in the molecule since pi bonds are not hybridized.

Julia Lee

I believe diamagnetism is when a molecule has no unpaired electrons and thus is not attracted to a magnetic field. The opposite is true for paramagnetism, in which the molecule is attracted to an outside magnetic field due to its unpaired electrons.

Julia Lee

This is simply due to the period number of Carbon.

Julia Lee

Yes. Lone pairs definitely do count as areas of electron density. If you look at a hybridized orbital, the paired electrons in an orbital represents the lone pairs in a molecule.

Julia Lee

Im guessing it has to do with the distortion of bond angles in a molecule due to lone pair repulsion.

Julia Lee

Yes, dipole-dipole interactions only occur between two polar molecules who have partial charges.

Julia Lee

How can you tell whether the compound is polar or nonpolar based on the shape of the Lewis structure? You can tell by drawing in dipoles on all bonds. If the dipole directions do not cancel out completely in a molecule, it is considered polar. A nonpolar molecule will have the same atoms around it ...

Julia Lee

Yes, all molecules will have London Dispersion forces because it is due to the random distortion of charge and all molecules have an electron cloud and a positively charged nucleus.

Julia Lee

The difference in electronegativity, the amount of bonds, and the melting/boiling point can also tell you whether a bond is strong or not

Julia Lee

the chart in the textbook is actually really helpful. As long as you can visualize it, it will be easy to remember the shapes and bond angles.

Julia Lee

No, I believe that ionic compounds are extremely polar molecules so even if they do show some covalent character, they will always be polar.

Julia Lee

Sigma bonds have an end-to-end interaction allowing bound atoms to rotate. They are always the first bond formed in a molecule and are the strongest bond due to the max amount of overlap. Pi bonds have a side-by-side interaction and do not allow bound atoms to rotate. They have e- density on each si...

Julia Lee

I believe intermolecular interactions, bond strengths & lengths, VSEPR, molecular shape & structure, sigma & pi bonds, and hybridization are all the topics that are going to be covered on test 3.

Julia Lee

Pi bonds are usually weaker than sigma bonds even though they are more rigid and do not allow bonded atoms to rotate. This is because for sigma bonds, molecules interact end to end linearly while pi bonds interact side-by-side, so there is much less overlap when you are looking at a pi bond.

Julia Lee

If you draw in the dipole moments (with the arrows) for all elements within a molecule and all dipole moments cancel each other out, than the molecule is nonpolar. If the dipole moments do not cancel each other out, than the molecule is polar. Also professor Lavelle described it in lecture that if a...

Julia Lee

Yep, that is correct. All angles will be slightly less than 90, 120, and 180 due to the lone pair repulsion.

Julia Lee

Why is Hydrogen bond shape not 90 degrees but 109 degrees I didn't understand that part. This is because in reality, molecules exist in 3 dimension, not 2. So in 3D, a molecule such as CH4 will try to maximize the distance between each bond, which will lead it to have 109.5 degrees between each bon...

Julia Lee

Yep, hydrogen bonding is a dipole-dipole force that is stronger than induced-dipole but weaker than the ion-dipole force.

Julia Lee

Does anyone know if we will need to know how to identify between lewis acids and bases for the midterm? I feel like we only briefly covered it in lecture.

Also, does anyone know general tips on how to identify between acids and bases when given a compound or molecule?

Julia Lee

kellyzhang1210 wrote:when we draw resonance structures, if it has a net overall charge of -2, do we have to bracket the drawing and write subscript -2?

Yes, that is correct

Julia Lee

I think that Lavelle said in lecture that generally, the lower electronegative element will be in the middle of the structure and then the other elements will usually form bonds around it. Also, Hydrogen only can bond once so it is never in the middle of a molecule.

Julia Lee

Bound atoms are more stable because they have a lower potential energy. If atoms are freely moving, they have a greater potential energy and thus are less stable.

Julia Lee

Hi, is the review session in Young Hall where our lectures are or is it CS24?

Julia Lee

The link says page not found.

Julia Lee

Im pretty sure that the degeneracy of a 3p orbital would just be 3 since 3px, 3py, and 3pz all have the same energy level in a multi-electron atom.

Julia Lee

I'm not really sure about why d is false but for part a, I recall that lavelle briefly mentioned that since UV light has a lower wavelength, therefore a higher frequency and energy than visible or infrared lights, most metals will emit light when a UV light is shone on it. Most metals need this high...

Julia Lee

Do any of you know if we need to know Coulomb's Law and Effective Nuclear Charge for the test? I know Lavelle gave us the equation in lecture Friday but we haven't really done much with it yet.

Julia Lee

Would we need to know Coulomb's Law and Effective Nuclear Charge? I know Lavelle gave us the equation in lecture Friday but we haven't really done much with it yet.

Julia Lee

Hey guys,
I was just wondering whether or not spin counted as being a part of an orbital. In the textbook questions, I don't think they were counted but im unsure as to why they aren't.

Julia Lee

Just to clarify, the Einstein Equation and the Photoelectric Effect describe particle behavior while the Debroglie Equation is used to describe wave behavior?
Also these equations the Uncertainty Principle px= h/4pi and E= -hR/n^2 describing energy levels work for both wave and particles?

Julia Lee

Hey guys,

So just to clarify, we cannot use the DeBroglie equation for light/photons since this is only applicable to things with resting mass?

Julia Lee

Hey guys, I'm really confused about the units that we use in the Quantum World. So if you're given the wavelength in nm, should we convert it to meters before solving the problem? Also what are the units for Energy? I know that energy can be given as Joules, eV, cal, and Watts. So if we are given on...

Julia Lee

So during lecture Professor Lavelle stated that this equation could only be used for Hydrogen atoms. Does this mean there are separate equations for other atoms that we will have to know or will we only be solving questions for H atoms for this class?

Julia Lee

Hi, can someone help me figure out how to solve L.35 part one of the homework question? A 1.50-gram sample of metallic tin was placed in a 26.45 g crucible and heated until all the tin had reacted with the oxygen in air to form an oxide. The crucible and product together were found to weigh 28.35 g....

Julia Lee

Hi, can someone help me figure out how to solve part b of M.5?

The question asks: The reaction 6CLO2 + 2BrF3 -> 6CLO2F + Br2, is carried out with 12 mol ClO2 and 5 mol BrF3.

Estimate how many moles of each product will be produced and how many moles of the excess reactant will remain.

Julia Lee

Hey, do any of you guys know whether there is a way to convert from Fahrenheit to Kelvin and vice versa without converting to Celsius first?

Julia Lee

Hey, do any of you guys know what the problem is telling us if it says that there is a combustion of whatever molecule? If we were writing a chemical equation for that would it just be whatever molecule + O2 ?

Julia Lee

For all addition, subtraction, multiplication, and division, the number of decimal places in the result should be the same as the smallest number of decimal places in the data/question. When rounding, if the last digit of the number is >5, round up. If the last digit is <5, round down, and if the la...

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