CHEMISTRY COMMUNITY

Mhun-Jeong Isaac Lee 1B

Yes as the above comments have stated, I believe it is best to use the equation involving Q. There were many times Dr. Lavelle advised against using some methods the book suggested.

Mhun-Jeong Isaac Lee 1B

I may be wrong but I believe the above comment might be inaccurate. The reducing agent has a reducing power because it is reducing another atom and the oxidizing agent has an oxidizing power because it oxidizes another atom. Correct me if I am wrong.

Mhun-Jeong Isaac Lee 1B

Raising both sides of the equation to the exponent of e will cancel the ln. You then solve for one of the K values.

Mhun-Jeong Isaac Lee 1B

Responding to an above question, yes it is possible for a cell potential to be negative. That’s why in galvanic cell problems, it is important to make sure it is positive or else it is not a galvanic cell.

Mhun-Jeong Isaac Lee 1B

Adding on, many questions deal with how temperature affects Gibbs free energy. For example, determining the temperature when the reaction changes from spontaneous to nonspontaneous is in other words finding the temperature when Gibbs free energy changes from a negative value to a positive value. So ...

Mhun-Jeong Isaac Lee 1B

Yeah a lot of people get it mixed up with the total moles of reactants and products but it is the electrons transferred. Always make sure it is the number of electrons after you balance the half-reactions and make sure the electrons cancel out.

Mhun-Jeong Isaac Lee 1B

The porous disk serves essentially the same function as a salt bridge. Both allow ion transfer so that the two solutions stay neutral.

Mhun-Jeong Isaac Lee 1B

Adding a salt bridge or porous disk allows ion transfer (two solutions stay neutral).

Mhun-Jeong Isaac Lee 1B

Yes for example if we look at the problem Dr. Lavelle gave in class: 8H+ + (MnO4)- + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O, Mn is reduced from +7 to +2.

Mhun-Jeong Isaac Lee 1B

To further complement the above responses, know that W = -PdeltaV is used to calculate work done by expansion against constant P. So since isobaric means constant pressure, this equation would be used.

Mhun-Jeong Isaac Lee 1B

Lyndon in his review session said that in this class, we can pretty much assume that isothermal means reversible.

Mhun-Jeong Isaac Lee 1B

Adding onto the above responses, just remember that reversible does maximum work and is always at equilibrium. In this class, reversible will be pretty much synonymous to isothermal.

Mhun-Jeong Isaac Lee 1B

A nice way to visualize is this: when you are decreasing the volume you are increasing the pressure. When you apply pressure to something, it would want to move to a place more open to lessen the pressure. This is the case for reactants and products experiencing increases pressure. The side with mor...

Mhun-Jeong Isaac Lee 1B

The only time when a change of pressure will have an effect is when the volume changes. A decrease in volume creates an increase in pressure. However the addition of inert gas does not change the volume and it does not react with the present reactants or products.

Mhun-Jeong Isaac Lee 1B

As the above responses have stated, K is the only factor that causes a change in K. Changes in elements like pressure, volume, or moles creates a Q which is temporary.

Mhun-Jeong Isaac Lee 1B

This is how Dr. Lavelle explained it. Positive delta H signifies that it is endothermic which means energy is being put into the system. Negative delta H is exothermic which means energy is leaving the system. In this way, you can rationalize the positive and negative better as gain and loss of ener...

Mhun-Jeong Isaac Lee 1B

Phase change from solid to liquid to gas requires energy in order for the bonds to be broken. Therefore, they are endothermic.

Mhun-Jeong Isaac Lee 1B

It helps to take a look at the phase change graphically. You would see that there is a lot more energy involved as the steam condenses to liquid. This heat energy, which is significantly greater than the energy liquid water holds, is being absorbed by the skin causing severe burns.

Mhun-Jeong Isaac Lee 1B

Looking at PV=nRT you can see that pressure and volume are inversely related. An increase in pressure results in a decrease in volume. And a decrease in pressure results in an increase in volume.

Mhun-Jeong Isaac Lee 1B

Look at how many mols are on both sides of the equation. If the pressure increases, the equilibrium shifts towards the side with less mols.

Mhun-Jeong Isaac Lee 1B

I am sure you would only look at aqueous and gases.

Mhun-Jeong Isaac Lee 1B

For me personally, I found that paying close attention to his lectures and doing most of the homework problems really prepared me for the tests, midterm, and final. A huge help is also Lyndon Bui's, the TA, review sessions. They are very thorough and refresh your memory on everything that was covered.

Mhun-Jeong Isaac Lee 1B

Yeah use K. Whenever you are confused as to which unit to use, look at the constant values in the equation and use the units that will cancel out with them. In this case of PV = nRT, R uses K.

Mhun-Jeong Isaac Lee 1B

Yeah just to confirm the above responses, Dr. Lavelle hasn't gone over that equation so I don't think we have to know that one. For now at least.

Mhun-Jeong Isaac Lee 1B

Lyndon said that when writing the symbols, it doesn't matter the order of the ligands. However, for the letter names, alphabetical order is necessary.

Mhun-Jeong Isaac Lee 1B

Dr. Lavelle has used chloro in his lecture notes so that would be a safe bet.

Mhun-Jeong Isaac Lee 1B

For example [Ni(CN)5]3- has a negative overall charge so you would add -ate to the end of nickel.

Mhun-Jeong Isaac Lee 1B

^I'm not too sure about that but I know that when drawing out the Lewis Structures, Dr. Lavelle wants the ligand bonded to the central ion to be written so that the atom with lone electron pairs is connected to the bond line. For example in the lewis structure for [NiCl2(NH3)4] . 2H20, it would look...

Mhun-Jeong Isaac Lee 1B

A chelation is a process in which a polydentate ligand bonds with a metal ion, forming a ring. The complex produced from this is called the chelate and the polydentate ligand is the chelating agent. More information I found was from this website: https://chem.libretexts.org/Textbook_Maps/Inorganic_C...

Mhun-Jeong Isaac Lee 1B

So for example, we have [NiCl2(NH3)4] . 2H20. Everything inside the square brackets is inside the coordination sphere. Ligands directly attached to central ion make up the coordination sphere.

Mhun-Jeong Isaac Lee 1B

Single bonds involve one sigma bond and double bonds involve one sigma and one pi bond. The importance of a pi bond is that it restricts rotation while sigma bonds do not.

Mhun-Jeong Isaac Lee 1B

Another way to understand it better is to have a visual of it. The unhybridized orbitals morph to become new hybridized orbitals which have been experimentally observed.

Mhun-Jeong Isaac Lee 1B

Yes you would only look at the regions around the central atom, not the bonded atoms.

Mhun-Jeong Isaac Lee 1B

Remember to name the shape of the molecule using position of only bound atoms (bonding electron pairs only). However, the molecular shape is determined by both lone pairs and bonding pairs because of repulsion.

Mhun-Jeong Isaac Lee 1B

Reiterating an above response, for many of the shapes, lone electron pairs causes angles to decrease. In that instance, you only need to know that the angle is less than an established value. For example, for trigonal pyramidal, you just need to know that the angle is less than 109.5 degrees. You wo...

Mhun-Jeong Isaac Lee 1B

So for example, in C2H2Cl2, C is bonded to Cl. The Cl would be more negative because it has a higher electronegativity, it wants electrons more than the C. Thus, the C would be more positive. These are the positive and negative dipole moments.

Mhun-Jeong Isaac Lee 1B

Lone pairs matter! The steric number is the amount of lone pairs and bonds the central atom has and so the steric number might be the same for multiple molecules but the shape of the molecule could be very different depending on the amount of lone pairs the atom has. For example, H2O has a steric n...

Mhun-Jeong Isaac Lee 1B

I'd say do the homework problems that relate to the information you learned in the most recent lecture, and maybe a few from previous lectures. It's possible to be docked off points for not including homework covering current material (I know from experience).

Mhun-Jeong Isaac Lee 1B

Hi in the lecture notes it said:
Repulsion strength: lone-lone pair > lone-bonding pair > bonding-bonding pair
Can anyone clarify what this means?

Mhun-Jeong Isaac Lee 1B

Just a reminder too that there are some exceptions in these trends like C, N, O, F. Make sure to look out for those.

Mhun-Jeong Isaac Lee 1B

Another way to look at it is how my TA defined them:
electron affinity = how much an atom "wants" an electron
electronegativity = polarizability, attracts electron in a bond

Mhun-Jeong Isaac Lee 1B

So electron affinity is how much the element wants an electron. The reason why the order for increasing electron affinity is N<C<O<F instead of the intuitive C<N<O<F is because C wants to reach a half-filled subshell, or 3 electrons out of the 6 electrons in the p subshell. Half-filled and completel...

Mhun-Jeong Isaac Lee 1B

Ionization energy is the energy required to take an electron away from an atom. In other words, a higher ionization energy signifies that it is harder to strip an electron away. It gets higher as you move from the bottom left to the top right of the periodic table because of higher proton counts and...

Mhun-Jeong Isaac Lee 1B

The anion is larger than the neutral atom because as stated above, the proton number stays the same but the electron number increases. So, while the positive attraction stays the same, the negative charge increases. This causes repulsion among the electrons which increases the size. However, if the ...

Mhun-Jeong Isaac Lee 1B

Just to add on to the above responses, as you go from the bottom left to the top right of the periodic table, the atomic radius generally gets smaller because there are less energy levels as you go up and more protons as you go to the right. More protons means that there is a stronger positive attra...

Mhun-Jeong Isaac Lee 1B

Test 2 will cover Quantum world but only up to Friday's lecture inclusive. Any material from Week 4 won't be on this test.

Mhun-Jeong Isaac Lee 1B

Dr. Lavelle gave the values red = 700 nm and violet = 400 nm in class lecture. So I would assume these numbers to be pretty reliable.

Mhun-Jeong Isaac Lee 1B

Just another reminder too is that Herz = s^-1. I find it helpful to convert Hz to s^-1 so that if units are being multiplied or divided, it's easier to see how things cancel out.

Mhun-Jeong Isaac Lee 1B

Saw a chem mod reply to someone saying we use nu. It's basically just a cursive v.

Mhun-Jeong Isaac Lee 1B

Yes, Lavelle said that the mass is given. So it is safe to assume that the mass will be on the constants sheet for any tests/exams.

Mhun-Jeong Isaac Lee 1B

Yes, what the two above have mentioned is correct. Also, Lavelle said in lecture that we will be mostly focusing on ultraviolet rays, visible light, and infrared rays in class so we don't have to worry about the others too much.

Mhun-Jeong Isaac Lee 1B

I would just like to underscore the importance of visualization as the previous response has stated. Before converting, I find it very helpful to compare the size of both units. For example, if I were to convert meters to kilometers, I would first realize that a kilometer is a larger unit than a met...

Mhun-Jeong Isaac Lee 1B

Allow me to reaffirm the statements of the above responses. I have physical evidence of Dr. Lavelle approval of the use of 6.022*10^23 for Avogadro's number in my notes that I have taken on the first lecture day.

Mhun-Jeong Isaac Lee 1B

Fascinating. Yes, based off of the work you have shown, it appears to to me that there should indeed be four sig figs. I believe the solutions manual at times chooses to disregard sig figs, so I wouldn't stress about it too much. I hope this response of agreement eases your conscience.

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