CHEMISTRY COMMUNITY

Qiu Ya Wu 4I

Will there be a time limit for the exam?

Qiu Ya Wu 4I

Will the UA sessions in Covel 210 still be going on tonight?

Qiu Ya Wu 4I

As always, homework problems are the most reliable source of practice for the exam so definitely make sure that you have done all the problems before the final!

Qiu Ya Wu 4I

Even though the assigned reading goes into this calculation in-depth, I doubt that we will have to know how to calculate it as he hasn't gone over it in lecture and there have been no homework problems that deal with the topic.

Qiu Ya Wu 4I

Usually, at least one question from the homework will appear nearly word for word on Lavelle's midterms and finals.

Qiu Ya Wu 4I

For the image above, it's good to know that only one intermediate will be formed since the reaction profile indicates a 2 step process and the intermediate will be created in the first step and used as a reactant for the second step.

Qiu Ya Wu 4I

To add on to the previous post, the presence of a catalyst will also not affect equilibrium concentrations or enthalpy!

Qiu Ya Wu 4I

How do I access Sapling Learning? I tried accessing it on a link he sent in one of his emails, but it required a payment method. The instructions said there was a way to avoid payment but I didn't see it. Upon buying the textbook for the course, you should have also received a pamphlet with a Sapli...

Qiu Ya Wu 4I

nicolely2F wrote:We will be given a sheet with all the half-reactions and standard potentials needed, though, right?

Yes, those will definitely be provided!

Qiu Ya Wu 4I

We use platinum and graphite as the electrode in our cell diagrams when there are no conducting solids present for the given half-reaction.

Qiu Ya Wu 4I

I don't believe that it is.

Qiu Ya Wu 4I

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? When presented with these kinds o...

Qiu Ya Wu 4I

In addition, a substance is in standard conditions when it has a molarity of 1M (aq), when it has a partial pressure of 1 bar (g), or when it can be considered a pure liquid or solid.

Qiu Ya Wu 4I

The Gibbs free energy of a redox reaction can be linked to its cell potential and Gibbs free energy can be interpreted as the maximum non-expansion work a specific reaction can do.

Qiu Ya Wu 4I

A general rule of thumb is that H will be +1 and O and S will be -2.

Qiu Ya Wu 4I

H+ and H3O+ are essentially the same thing so you could theoretically use them interchangeably. However, since H3O+ is more useful for when we are dealing with proton transfer, H+ would be the more efficient one to use.

Qiu Ya Wu 4I

Will test 2 cover concepts like rust/corrosion and pH meters? Some of the later homework questions deal with these topics but Lavelle has not gone over them during lecture.

Qiu Ya Wu 4I

I don't believe the cell potential for the Au+ -> Au3+ + 2e- half reaction, the one that I expected, is given in the back of the book either. I'm commenting down below so I can return to this post when more answers have been posted.

Qiu Ya Wu 4I

A word of caution: an UA told me that the book is really inconsistent with the visual diagram conventions so I would always double check!

Qiu Ya Wu 4I

Can someone please explain to me what an oxidizing/reducing agent is? From the homework problems, it seems as if the compound losing electrons is the reducing agent and the compound gaining electrons is the oxidizing agent but that sounds incorrect to me.

Qiu Ya Wu 4I

I believe Lavelle has said that he will be finished lecturing for Test 2 material after Monday next week.

Qiu Ya Wu 4I

Essentially all problems in the textbook up to what Lavelle has covered so far can be fair game!

Qiu Ya Wu 4I

Is the overall oxidation number for ozone 0? How could this occur if the oxygen atom is commonly regarded to have an oxidation number of -2?

Qiu Ya Wu 4I

viewtopic.php?f=160&t=58424

Here is one of them!

Qiu Ya Wu 4I

Seeing as the class average was about a B+ for CHEM 14A, I would not expect a sizeable curve.

Qiu Ya Wu 4I

Jessica Esparza 2H wrote:It is uniform graders. Does anyone know if it'll take about a week like last time?

Yes they should be handing back the midterm at the end of lectures about a week from now!

Qiu Ya Wu 4I

The second test will likely cover the end of outline 4 and outline 5!

Qiu Ya Wu 4I

I'm not sure about the exact details of the question, but the answers for the midterms should be posted soon on Lavelle's website complete with step by step solutions and a point breakdown!

Qiu Ya Wu 4I

Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The containers all ...

Qiu Ya Wu 4I

He has not posted it yet! But I would definitely be on the lookout as he should be uploading it soon.

Qiu Ya Wu 4I

The first law of thermodynamics is the change in internal energy = heat + work and the second law is delta S = q/T.

Qiu Ya Wu 4I

In addition, you can think of the temperature remaining the same due to all the added heat being used to break the bonds between molecules of a substance.

Qiu Ya Wu 4I

I think it would be good to remember that entropy is an extensive property!

Qiu Ya Wu 4I

He typically posts a worksheet on chemistry community! He'll probably let us know what to type in the search bar to find it in the following days.

Qiu Ya Wu 4I

An UA told me that we were going to cover material up to Outline 4. There are usually a bunch of review sessions that are held by BOTH lavelle and the UA's so definitely be on the lookout for those!

Qiu Ya Wu 4I

Enthalpy at constant pressure is referring to essentially an open system with an air pressure of 1.0 atm. With an open system, the gas has the ability to push the air on top of the beaker out of the way, therefore performing work onto it.

Qiu Ya Wu 4I

In order to use Hess's Law to solve for the change in enthalpy, you will have to know the changes in enthalpy for intermediate reactions that occur with the reactants given to form the end product.

Qiu Ya Wu 4I

Are you referring to the example dealing with the combustion of methane? If so, I don't believe that we needed to calculate the mass, but rather the change in enthalpy by adding up the sum of the standard enthalpies of formation for the products and subtracting the sum from the standard enthalpies o...

Qiu Ya Wu 4I

During the lecture, Lavelle instructed us that q(p)=delta H!

Qiu Ya Wu 4I

Yes I had that issue too! I believe it's an error on the solution manual.

Qiu Ya Wu 4I

For the purposes of this course, acid/base reactions are reversible only with weak acids or bases.

Qiu Ya Wu 4I

I think it would be a good idea for you to memorize the chemical formula just in case! It's relatively straight forward.

Qiu Ya Wu 4I

pH measures the amount of H3O+ ions produced due to the reaction. The more H30+ ions a reaction can produce, the more acidic it is. It might also be helpful to remember that pH and the concentration of H3O+ ions are inversely related.

Qiu Ya Wu 4I

To add on, this system works this way due to Le Chatelier's principle since favoring the side of the reaction with less moles of gas when pressure is applied means that there will be less molecules ultimately bouncing off the walls of the container and creating additional pressure.

Qiu Ya Wu 4I

Increasing the total pressure of the system will cause equilibrium to shift to the side with fewer moles Changing the pressure of a system will not change the equilibrium constant k itself, but it will cause a net increase in the equilibrium concentration of the side of a reaction with less moles d...

Qiu Ya Wu 4I

but can't you also use Kc for gases? so the phases don't really tell you anything but just go off of what you're given? You can also use Kc for gases since a lot of the reactions we deal with have heterogeneous equilibria. If the units for the amount of gas are in L/mol, use concentration and if th...

Qiu Ya Wu 4I

Solids and liquids aren't included in the equilibrium constant because there's no such thing as the "concentration" of a solid and liquids (solvents) can usually be expected to have nearly the same concentration on both sides of the equation so they would cancel out to 1 anyways if we divi...

Qiu Ya Wu 4I

Lavelle gives you 4 different values for the R constant on his formula sheet during tests. Whichever one you use depends on the units given in the problem.

Qiu Ya Wu 4I

None of Lavelle's lectures are recorded during the quarter with the exception of his lecture series on early chemical equilibria posted on his website.

Qiu Ya Wu 4I

I don't believe that Lavelle has gone over that topic in lecture yet but seeing as it's listed on the outline and not mentioned in the books, I'd advise you to make a habit of attending his lectures as oftentimes he likes to emphasize specific concepts about biological examples such as this that may...

Qiu Ya Wu 4I

We move elements of the equation around to solve for P and the concentration so we can convert the partial pressure of a gas to its concentration. Being able to do so will be helpful when we deal with heterogenous equilibria.

Qiu Ya Wu 4I

The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calculate the equilibr...

Qiu Ya Wu 4I

In one of Lavelle's video lectures he asserted that we will treat 1 bar as equal to 1 atmosphere for the purposes of this course.

Qiu Ya Wu 4I

Sapling learning assignments did not account for any portion of our grade last quarter for 14A!

Qiu Ya Wu 4I

Q is known as the reaction quotient and K is known as the equilibrium constant. One important thing to note is that K stays constant for a specific reaction at a specific temperature while Q does not have a predetermined value.

Qiu Ya Wu 4I

Generally, only molecules arranged in planar arrangements, such as linear, trigonal planar, square planar, and perhaps t-shaped (please correct me if I am incorrect) contained atoms that are considered to be on one plane.

Qiu Ya Wu 4I

Additionally, there are instances of acidic anions (when the reactant is polyprotic). The book goes into this in detail and there’s a chart of that lists the few times this occurs.

Qiu Ya Wu 4I

I left 30 minutes in but keep us updated on whether or not he shows!

Qiu Ya Wu 4I

I just stumbled upon this section in my lecture notes and to add on to what everyone has been saying, Lavelle clarified that the hydrated metal cation will release H+ ions to form hydronium ions with water until the overall charge of the ion becomes neutral. When this happens, any anions attached to...

Qiu Ya Wu 4I

"When copper(II) nitrate dissociates in water, it forms Cu2+ and NO3-. Cu2+ is acidic since it is a transition metal, and NO3- is neutral because its the base of a strong acid, so it's relatively weak and doesn't do anything (spectator ion)." Lavelle gave this answer when answering another...

Qiu Ya Wu 4I

2HI(aq) + CaO(s) --> CaI2(aq) + H2O(l)

Can someone explain the chemical reaction that is going on here and why CaO is a base? I understand why HI functions as an acid since it can pretty easily give off the H+ ion, but I'm not sure how these reactants form those products.

Qiu Ya Wu 4I

I think it would be helpful to memorize the charges for the common polyatomic ions since it's not guaranteed that Lavelle would provide them on the final; it could save you a lot of time with the oxidation number calculations for coordination compunds if these ions show up as ligands as well.

Qiu Ya Wu 4I

Assuming that HBr + K+(OH)- --> KBr + H2O is your intended reaction, this reaction is an example of a neutralization reaction, which you could read more about in Fundamentals J.3. The H+ ion dissociates with the Br in the presence of a metal hydroxide (KOH-) since HBr is a strong acid and KOH- is a ...

Qiu Ya Wu 4I

Bronsted acids are defined as proton donors while Bronsted bases are defined as proton acceptors. In this case, the NH3 is a Bronsted base since a H+ ion (really just a proton) could bond to the N as it has an extra unoccupied bonding site. I'm not sure if you could make the generalization that mole...

Qiu Ya Wu 4I

Can someone explain to me how molecules such as NH3 displace the water molecules bonded to a metal ion in an aqueous solution during a chemical reaction?

Qiu Ya Wu 4I

Would the edta ligand form an octahedral complex when it bonds with a metal ion since it is hexadentate and has the coordination number 6? If so, would the entire ligand have to wrap around the metal ion? Additionally, why are the points of attachment for the edta ligand only on the N atoms and the ...

Qiu Ya Wu 4I

I think the exact bond length and dissociation energy for a molecule is something that has to be experimentally determined. He might ask you to compare the bond lengths of certain molecules, but general rules concering atomic radii should be able to help you compare their lengths qualitatively.

Qiu Ya Wu 4I

Does a trigonal bypryramidal shape have bond angles of 90, 120, AND 180? I have 180 degrees written down in my notes as well but the book seems to exclude it and only states the angles of 90 and 120.

Qiu Ya Wu 4I

Can nonpolar molecules still have dipole-dipole interactions even though they have a net dipole of zero?

Qiu Ya Wu 4I

What exactly does "cylindrical symmetry around the internuclear axis" mean? I understand that it has something to do with allowing the molecule to rotate while still maintaining an overlap of the bonding orbitals, but I'm having a difficult time visualizing "cylindrical symmetry".

Qiu Ya Wu 4I

Is there any way to reason why the bond angle between NH3 is larger than the bond angle of SO3(2-)? I believe Lavelle sort of touched on why it makes sense for one to have a bond angle of 107 degrees and the other to have one of 106 degrees but I didn't manage to catch his explanation.

Qiu Ya Wu 4I

Ghadir Seder 4F wrote:Whats the first topic that lavelle lectured about after our midterm?

I believe the first lecture after the midterm on last Friday went in further detail in regards to principles of chemical bonding, more specifically induced dipole-induced dipole bonding and hydrogen bonding.

Qiu Ya Wu 4I

I think that we are expected to recognize the shapes of simple molecules up to octahedral, as Lavelle didn't go over pentagonal bipyramidal in class. I wouldn't be surprised if a question on the bond angle between a specific trio of atoms came up on the test, so memorizing those would also be helpful.

Qiu Ya Wu 4I

Yes! Lone pairs also have a stronger degree of repulsion since there's only one positive force that counteracts the energy of a lone pair, namely the nucleus of the atom to which the lone pair belongs to while bonded pairs have 2 positive nuclei in between them which act as 2 positive forces that co...

Qiu Ya Wu 4I

I think this equation was referenced by Lavelle to emphasize the importance of the distance between two bonded atoms and their charges in determining the strength of a bond and whether the resulting compound is a solid, liquid, or gas. I think the more generalized equation, the one listed on the las...

Qiu Ya Wu 4I

I believe Test 2 will test on the topics posted on Outline 4 and will include topics like induced dipole-induced dipole bonding that were omitted from the midterm and on Chapters 2E-2F, which Lavelle should be able to cover within the next three lectures.

Qiu Ya Wu 4I

I don't think Lavelle expects us to know how which molecular formula corresponds to which molecular name but I think starting to look at a list of common polyatomic ions (there's only around 10-20 of them) and studying prefixes and suffixes would be a good place to start studying.

Qiu Ya Wu 4I

I don't believe it is part of Lavelle's outline but I would recommend studying it as it's not a hard concept to grasp and can help you immensely in drawing lewis structures.

Qiu Ya Wu 4I

Thanks for the support! Good luck to you as well tomorrow :) I would also recommend double checking the location of your midterm since everyone gets split up.

Qiu Ya Wu 4I

Wavelike properties fail to be detected past 10^-15m. For reference, an electron has a wavelength of 10^-12 m and an Angstrom is 10^-10m.

Qiu Ya Wu 4I

Through my studies for the midterm, I came across the detail that passing an electric current through hydrogen gas causes electromagnetic radiation of a certain frequency to be emitted as an electron goes from a higher to a lower energy level. Given this, why does an electron, and not electromagneti...

Qiu Ya Wu 4I

Electronegativity follows the same general trend as ionization energy, increasing as you go up and to the right!

Qiu Ya Wu 4I

I believe you have mistakenly replaced indium with tellerium in your final answer. The correct answer is In<Sn<Sb<Se, which you should have arrived at based on your thought process if you didn't switch up the two elements

Qiu Ya Wu 4I

Angstrom is a non-SI unit that is preferred in calculating bond lengths; one angstrom is equivalent to 10^-10 m. I believe it would be wise for you to memorize the conversion between angstrom and meters as this is an unit that will probably show up repeatedly in future chemistry courses.

Qiu Ya Wu 4I

Threshold energy and ionization energy both have to do with the minimum energy required to remove an electron from an element but threshold energy refers to the energy needed to remove an electron from a metal (photoelectric effect) while ionization energy has to do with the energy needed to remove ...

Qiu Ya Wu 4I

Noble gases are the least reactive and most stable out of all the elements in their period, but I'm uncertain as to whether this puts them at a lower energy level since their valence electrons are still filling the p subshells, which are higher in energy than the s subshells. Fulfilling hunds rule c...

Qiu Ya Wu 4I

I think this week was more focused on building upon prior concepts in the Quantum World unit as we have barely delved into the new unit so I would do my homework on the questions in Outline 2! However, if you'd like to move ahead I'm sure the questions on Outline 3 are fair game as well.

Qiu Ya Wu 4I

A triple bond is most stable since the bonds have shorter lengths, thereby holding the electrons more tightly together.

Qiu Ya Wu 4I

I believe that it would just be far more reasonable for these atoms to gain/lose electrons to fulfill the 1s shell rather than gaining all those excess electrons to fill the entire 2nd shell.

Qiu Ya Wu 4I

The element with the lowest ionization energy is the central atom since it takes the least amount of energy for an electron to detach from the atom. This means that it can more readily form bond(s) with other atoms.

Qiu Ya Wu 4I

Writing out the d block elements' electric configurations would help you immensely in counting their valence electrons! Just remember to only count electrons in the outermost shell. The electron configuration of Zinc is formally [Ar] 3d¹⁰4s², but you should only focus on the electrons in the outermo...

Qiu Ya Wu 4I

I didn't realize that the homework problems list specifically told us to skip this problem (1E.21 c) so I went ahead and tried to figure out the electron configuration of tantalum and arrived at Xe 4f7 5d10 6s2, which is far from the correct answer. I'm curious as to whether there's a fundamental pr...

Qiu Ya Wu 4I

Since there are two possible electrons that can have the same n,l, and m quantum numbers, we use +1/2 and -1/2 spin to distinguish them. For that reason, there can only be 2 spin states.

Qiu Ya Wu 4I

The ground state can also be described as the lowest possible energy level that the atom can occupy and can be represented in a hydrogen atom when n=1 as -hR.

Qiu Ya Wu 4I

I think those 3 equations basically cover the fundamentals of quantum mechanics, but there are several other equations that form the intermediate steps of those equations such as c=λv, E=hv, E=pc, p=mv, E(n)=-hR/N^2, λ=h/p, and E(k)=1/2mv^2 that would be helpful to keep in mind.

Qiu Ya Wu 4I

In his lecture today, Lavelle emphasized that the plane the electron is found in is arbitrary and different textbooks associate different l values with different x,y, and z planes.

Qiu Ya Wu 4I

I believe the 4d orbital has a higher energy level than the 5s orbital, but not the 5p orbital. The graph I linked below might be helpful. https://webs.anokaramsey.edu/chemistry/ ... iagram.PDF

Qiu Ya Wu 4I

My TA actually handed out a copy of equations that Lavelle provides on the test sheet. For Test 1, the only relevant formula is that of Avogadro's constant. I imagine it will be much more helpful for tests later in the year as it includes a lot of fundamental constants and equations from the quantum...

Qiu Ya Wu 4I

My TA specifically referred us to review H7, L35, M9, and M15 during our discussion as they were considered the more complicated problems of the bunch. I would look over them before the test just in case!

Qiu Ya Wu 4I

The test covers topics beyond what was covered in the Audio-Visual focus topics! I believe a comprehensive list of concepts it will test us on are bullet pointed on Outline 1.

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