CHEMISTRY COMMUNITY

Jesalynne 2F

LOL this definitely helped lighten the mood

Jesalynne 2F

I think that Lavelle makes the final and the midterm and the TAs make the tests.

Jesalynne 2F

I think he'll use a similar grading scale. The syllabus just says that the cut off for a C- is 50% and nothing in the emails has indicated that the grading scale would be changed.

Jesalynne 2F

Hey guys, I've been finding it really hard to focus with everything that has been going on. Does anyone have tips on how to stay focused? I've been trying to study and it has been hard with all the updates for next quarter and the stress from that. Any tips would be appreciated! Thanks in advance. :)

Jesalynne 2F

My TA just had us email our week 10 homework to her. :) You can probably do the same.

Jesalynne 2F

Most likely we'll have to turn in the final online. :)

Jesalynne 2F

I like going through the homework problems to practice doing problems and going through the worksheets from discussion. I like to attend the review sessions that go over the topics I am not understanding or have questions about. Drop-in sessions or office hours would be a good resource if you had sp...

Jesalynne 2F

I think it would be okay for you to assume that the cathode is one the right and the anode is on the left.

Jesalynne 2F

The number of electrons should be balanced on both sides. You can multiply to get them to equal each other.

Jesalynne 2F

This is what I found for the review sessions days and times: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Final_Review_Sessions_14B.pdf

Jesalynne 2F

For a first order reaction the graph has -k slope and the graph is linear. The reaction rate is proportional to one of the reactants concentration.

Jesalynne 2F

It would probably be helpful to know how to derive it, but you would probably be okay just knowing the equations relationships.

Jesalynne 2F

I would think examples that we are expected to know would be in our notes or possibly from a homework question. For 14A the biological examples that we got on exams were covered in class.

Jesalynne 2F

For homework 9 I would think you can do homework from the topics that are going to be on test 2 in order to get some more practice in (2nd and 3rd laws of thermodynamics 2nd page and electrochemistry), or you can do homework from kinetics.

Jesalynne 2F

Test 2 will only cover from the midterm up until the material we covered before kinetics.

Jesalynne 2F

There are no extra credit opportunities. In 14A for Lavelle extra credit wasn't offered and it's not in the syllabus, so I assume there won't be any opportunities for extra credit.

Jesalynne 2F

A conjugate base will have one less proton than the acid and the conjugate acid will have one more H+ than the base.

Jesalynne 2F

The cathode is where reduction occurs and the anode is where oxidation occurs. I don't think it necessarily matters what side of the diagram it is on, but the anode is usually on the left side of the diagram and the cathode is on the right side.

Jesalynne 2F

When delta G is negative the reaction is spontaneous, but when delta G is positive the reaction is not spontaneous. When delta G is equal to 0 then the reaction is not spontaneous because it is at equilibrium.

Jesalynne 2F

Test 2 won't cover material that we'll learn this coming week. The test will cover material from after the midterm, which is the second page of outline 4 and outline 5.

Jesalynne 2F

In order to see which way the reaction will shift you would count the coefficients.

Jesalynne 2F

Cp and Cv are used in finding the heat capacity. Cp is for constant pressure and Cv is for constant volume.

Jesalynne 2F

There is not a curve, but in order to pass the class with a C- you need at least a 50% for your overall grade.

Jesalynne 2F

At constant pressure deltaH will be equal to q and at constant pressure it is for a phase change.

Jesalynne 2F

Yes, this can be used. You would need to plug in the standard temperature and pressure (273 K and 1 atm).

Jesalynne 2F

We will get the same equation sheet that is on his 14B website.

Jesalynne 2F

You will want to use the constant that has the units that apply to the problem you are solving; you will want the units to cancel to give you the unit you want your answer to be in.

Jesalynne 2F

If the pressure is increased the reaction would want to go back to equilibrium, so the reaction will shift to the side with fewer gas particles. If the pressure were to decrease then the reaction would go towards the side with more gas particles.

Jesalynne 2F

For a reverse reaction the value of K would be 1/K which is the inverse.

Jesalynne 2F

I believe that will be included, but like others have said before the midterm will cover content from the the first outline all the way up until the first page of outline 4. The content all the way until this past Friday's lecture will be included.

Jesalynne 2F

Yes, I believe your line of thinking is correct. :) That is what I have in my notes.

Jesalynne 2F

I am pretty sure you are correct and the answer should be 28 J. I found an old post on chemistry community and that was said to be the correct answer. Also, in my solution manual (old one but the same question) the answer is 28 J. Older post with this question: https://lavelle.chem.ucla.edu/forum/vi...

Jesalynne 2F

Like others have said, you would use the quadratic formula when you have x squared and you need to find the value of x. I found this to be helpful: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equil...

Jesalynne 2F

P is pressure, V is volume, n is the number of moles, R is the gas constant (it'll be given to us on the equations and constants sheet), and T is temperature.

Jesalynne 2F

If Q is greater than K, then the reaction will go towards the reactants. If Q is less than K then the reaction will go towards the products.

Jesalynne 2F

They were used as an example in lecture, so we won't be expected to draw them.

Jesalynne 2F

If the pressure is increased the reaction will go towards the side with fewer gas particles. If you decrease the pressure the reaction will go to the side with more gas particles.

Jesalynne 2F

This helped explain it for me: http://scienceline.ucsb.edu/getkey.php?key=1322 More energy is released in a phase change from a gas to a liquid (steam would turn to liquid once it touches skin) compared to boiling water touching skin because it doesn't undergo a phase change (less energy released). ...

Jesalynne 2F

For water to go from a gas to a liquid more energy is required. When the gas turns to a liquid on skin more energy is released than boiling water hitting skin because the boiling water doesn't undergo a phase change. This explains it further: http://scienceline.ucsb.edu/getkey.php?key=1322

Jesalynne 2F

I find that the Organic Chemistry Tutor really helps, and he does practice problems in the videos too. If you wanted more practice the problems in the book might help since you can check the odd numbered ones in the solution manual.

Jesalynne 2F

K is used when the reaction is at equilibrium and Q can be used for other random times in the reaction. Q can be compared to K to see which direction the reaction will go.

Jesalynne 2F

When Q<K you have more reactants, so more products form.

Jesalynne 2F

Since K is less than 10^-3 more reactants are at equilibrium and the reaction sits to the left.

Jesalynne 2F

The R constant will be provided on the "Constants and Formulas" worksheet which can be found on the 14B class website and will be provided on tests and midterms, so we will not have to remember it. The constant can change depending on what units it is in, but different unit forms are also ...

Jesalynne 2F

I believe in lecture Lavelle said that test 1 will be outline 1 and 2, which is chemical equilibrium and acids and bases.

Jesalynne 2F

K_p is used when dealing with gases, it is the equilibrium constant calculated from the partial pressures.

Jesalynne 2F

I doubt we'll have to memorize any K values. If anything we'll be given that information if it is required to solve a problem.

Jesalynne 2F

I believe we will be tested on outline 1 and outline 2 (or at least parts of outline 2 depending on how far we get). He does let us know what we'll be tested on, but if anything your TA should know too. :) I believe the TAs make the tests so homework problems might not be on the test but they'll be ...

Jesalynne 2F

It depends on the TA I think. Last quarter my TA graded on correctness but others graded on completeness.

Jesalynne 2F

Test 1 will be given in your discussion section during week 3.

Jesalynne 2F

I think these are all/the majority of the transition metals with Latin names (this applies when they are in anionic complexes):
Iron - Ferrate
Copper - Cuprate
Lead - Plumbate
Silver - Argentate
Gold - Aurate
Tin - Stannate

Jesalynne 2F

Thank you so much this is really helpful!

Jesalynne 2F

I think at the review session they said the answer was C=O because the the atomic radius of oxygen is smaller so it'll form a stronger bond.

Jesalynne 2F

You do not need to remember the mass of an electron since it is one of the constants that will be given on the formula sheet provided. The formula sheet will the same one from the midterm.

Jesalynne 2F

I think for pH sig figs you count the sig figs after the decimal point, at least that's what I remember hearing from a review session. I found an old post that might answer your question better: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=790

Jesalynne 2F

There was an email sent out that said review sessions would begin December 3rd, but the rooms and times haven't been announced yet, they will be announced Monday in class.

Jesalynne 2F

The final is cumulative and good review would be homework problems, tests, the midterm, and past final questions.

Jesalynne 2F

It should probably be posted in the next few days, but my TA already input grades so when grades are input probably depends on the TAs.

Jesalynne 2F

Single bonds are sigma bonds, in double bonds there is a sigma and pi bond, and in triple bonds there are two pi bonds and one sigma bond.

Jesalynne 2F

Based on the midterm there will probably be more calculation problems, but conceptual problems will be on the final as well.

Jesalynne 2F

Intermolecular forces affect the melting points, so the stronger the intermolecular force the higher the melting point and vice versa.

Jesalynne 2F

Electronegativity increases up and to the right of the periodic table. It also helps to remember that fluorine is the most electronegative element so electronegativity increases in the direction of fluorine.

Jesalynne 2F

The two terms are synonymous, so you can use either one. :)

Jesalynne 2F

If you're asked to give the quantum numbers for an atom or an ion you can write out the electron configuration of it and from there you can easily find out the quantum numbers.

Jesalynne 2F

Since lone pairs repel the other bonds around the central atom the bond angle between bonds will decrease since they arrange themselves to be away from the lone pair(s).

Jesalynne 2F

When determining the molecular shape and bond angles do the Lewis structures have to be drawn as accurately as possible?

Jesalynne 2F

I am not sure about “taking up space,” but lone pairs have a high repulsion force so they distort the bond angles and force the bonding pairs in the molecule closer together.

Jesalynne 2F

We may not be asked specific questions on periodic trends like we were on the midterm, but the topics we will be tested on rely on knowledge that comes from the periodic table. Since the test will cover material after the midterm we will be focusing on outline 4 and a little bit on outline 3 (things...

Jesalynne 2F

The number of significant figures you put your answer in is based on the question, so the least amount of significant figures in the question is used.

Jesalynne 2F

The majority of the test will probably focus mainly on outline 4 (molecular shape and structure) and a little bit of material from outline 3 may be on there too since things like London forces, dispersion forces, etc. were covered after the midterm I believe.

Jesalynne 2F

Yes, you are correct. :) Electronegativity increases up and to the right of the periodic table.

Jesalynne 2F

Iodine exists as a solid at room temperature because the strength of London forces are in line with iodine's large electron cloud and polarizability. I can't explain it that well, I'm sorry! But this article might be more helpful: https://socratic.org/questions/elemental-iodine-is-a-solid-at-room-te...

Jesalynne 2F

The greater the number of electrons there are and the greater distance of electrons from the nuclear charge, the less control the nuclear charge has on charge distribution, therefore there is an increased polarizability of the atom.

Jesalynne 2F

You should be fine doing homework from outline 3, since I don't think we've covered material from outline 4 yet. :)

Jesalynne 2F

The magnetic quantum number (m_l) is based on l, the angular momentum quantum number, and ranges from -l to l. So, if l=1 then m_l=-1,0,1.

Jesalynne 2F

Shorter bonds are stronger than longer bonds. The strength for three types is triple bond>double bond>single bond, so the stronger bonds are shorter.

Jesalynne 2F

Afbau states that the lower energy levels must be occupied before the higher ones can be filled and Hund’s rule states that the orbitals must be filled with one electron before they can be paired.

Jesalynne 2F

I think the midterm will be free response/open ended questions. If there are any multiple choice questions there will probably only be a few.

Jesalynne 2F

You would write the noble gas that comes before the element you are trying to write the electron configuration number then write the electron configuration for additional electrons in the regular way. I found watching videos helped me more than reading explanations so that might help you too! This o...

Jesalynne 2F

This is false because Zeffe is affected by the number of electrons in an atom because the electrons are shielded from the full attraction of the nucleus. This occurs because the electron electron repulsions work against the pull of the nucleus.

Jesalynne 2F

Thank you! Do you have any recommendations for how to review how to write the shorthand configuration?

Jesalynne 2F

For the midterm will we have to know how to write the shorthand electron configuration of an element?

Jesalynne 2F

When we draw the resonance structures do we have to draw out all of the possible ways or is a resonance hybrid sufficient enough on its own? Or would we have to draw all of the structures plus the hybrid?

Jesalynne 2F

I'm pretty sure you can do problems from both since we covered both sections. Like someone said before it might be beneficial to do problems from the chemical bonds section to get more practice on those problems since it'll be on the midterm.

Jesalynne 2F

I think one of the suggested ways to prepare for an exam was to work through the assigned homework problems. I would do those problems and study with someone else so we could ask each other questions and teach each other.

Jesalynne 2F

Is there an easy way to memorize the regions with the corresponding values? Do you use any mnemonic devices?

Jesalynne 2F

The answer would be d, because the photoelectric effect was explained to have electromagnetic radiation and it’s composed of photons that each have fixed energy that equals to h*v.

Jesalynne 2F

I think you would use the wavelength you got from part c and find where it is on the electromagnetic spectrum. There is a figure and table in 1A.2 Electromagnetic Radiation that you can refer to.

Jesalynne 2F

There is a constants and equations sheet posted on the website and I think that is the one we will be given on exams.

link: https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf

Jesalynne 2F

Hertz is cycles per second and it can be written as 1/s or s^-1

Jesalynne 2F

I don't think sig figs were really important for this test, but if they were to grade based on that you would just base your sig figs off the values given to you in the question. I hope this helps :)

Jesalynne 2F

I think you use the least amount of significant figures based on the values of what is given in the question, but I would definitely check out the post mentioned post to make sure. :)

Jesalynne 2F

Just to clarify, we are going to be expected to know the equations we have been given in class regarding light, energy, etc. right? Just asking because on the test they did give us an equation sheet with most of the equations.

Jesalynne 2F

The energy threshold won’t be enough to create the photoelectric effect but the energy will be conserved. The energy might be reabsorbed or refracted.

Jesalynne 2F

I just want to make sure I'm understanding your question :) are you asking what happens if the photon doesn't have enough energy to remove the electron?

Jesalynne 2F

I'm guessing if there are any questions in the homework like that then it'll be considered fair game. There is review in the textbook which would probably help with this or other resources like khan academy really help.

Jesalynne 2F

I heard Dr. Lavelle say during lecture that they are due Sunday night by 11:59pm

Jesalynne 2F

You wrote the correct prefixes for each conversion :) and I think to be safe you should know them in order to convert during tests, midterms, etc. in case it is required. Also, Dr. Lavelle mentioned that in chemistry we won't be using the larger units, like giga, often.

Jesalynne 2F

In order to find the total mass of the tin oxide you would use the total mass of the crucible and the product (28.35 g) and subtract that by mass of the crucible (26.45 g) to get the mass of the product formed. 28.35 g - 26.45 g = 1.90 g In the question they gave you the mass of tin (1.50 g Sn) so t...

Jesalynne 2F

Should I just use significant figures in my final answer or should I use them throughout the entire process leading up to my answer?

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