CHEMISTRY COMMUNITY

AKhanna_3H

Jared Khoo 1G wrote:Will the final still account for the 180 points on the syllabus or will it be worth less?

He said in an email that it is still 180 points but it will be short.

AKhanna_3H

For this question how can you tell which metals are the most strongly reducing?

AKhanna_3H

Will we be able to get partial credit for answers on the final if it is electronic?

AKhanna_3H

Could someone explain part b of this question? I understand that the slow step of the reaction determines the rate but how do you replace the intermediate in the rate law using the other steps in the mechanism?

AKhanna_3H

I think they are cancelled but we still need to email our TA our week 10 homework.

AKhanna_3H

Mariah wrote:
Rosa Munoz 2E wrote:No idea. We're all waiting on Lavelle's email

We won't have to be on campus right?

Since it's a take home test we most likely won't have to be on campus, just need access to wifi.

AKhanna_3H

The questions on the 14A final were fairly even in terms of material from the whole quarter, so I would assume it will be the same for 14B.

AKhanna_3H

For part c of this question, it asks what the effect of raising the temperature on the rate constants. What are the general trends of raising the temperature for endothermic and exothermic reactions?

AKhanna_3H

I think there will be an announcement in class tomorrow if you are referring to Lyndon's review packet

AKhanna_3H

The graph will be linear with a slope of -k

AKhanna_3H

I do not believe that we will need to know the derivations. I would only think that we would need to if it is explicitly stated on the outline sheets.

AKhanna_3H

My TA confirmed that it is an error in the solution manual because there should only be 1 e-, so your answer is correct!

AKhanna_3H

When do we include these in a cell diagram?

AKhanna_3H

The second page of outline 4 and all of outline 5. I usually do all of the practice problems on the outlines to prepare for the tests and I find that every topic is covered.

AKhanna_3H

If not told, you can figure out which is which by calculating what would make the overall cell potential positive. You could find the individual cell potentials for each half reaction, and then determine which would make E(cathode) - E(anode) a positive value.

AKhanna_3H

They can be on either side, the equation just needs to be balanced

AKhanna_3H

Test 2 will only cover the second page of outline 4 and all of outline 5.

AKhanna_3H

I'm not sure if you can use this logic with every problem, but I think you would determine which is which by calculating what would make the overall cell potential positive. So you could find the individual cell potentials for each half reaction, and then determine which would make E(cathode) - E(an...

AKhanna_3H

Whatever was not covered on the midterm, so the second page of outline 4

AKhanna_3H

Oxidation is the loss of electrons, so the oxidation number increases. Reduction is the gain of electrons, so the oxidation number decreases.

AKhanna_3H

The second page of outline 4 and all of outline 5

AKhanna_3H

Assume pressure is 1 atm and temperature is 273 K

AKhanna_3H

Solids and liquids are not included in equilibrium constants. Only gases and aqueous solutions are included.

AKhanna_3H

If the system is at equilibrium, you can replace Q with K in the equation.

AKhanna_3H

Yes, this equation can be used for STP.

AKhanna_3H

A phase change is when something goes from a solid to liquid (fusion), liquid to gas (vaporization), solid to gas (sublimation), or the reverse of these. In terms of equations to use, I assume you are talking about finding the q value, or amount of heat, associated for that phase change. In this cas...

AKhanna_3H

Only include gases and aqueous solutions. Disregard solids and liquids.

AKhanna_3H

For this problem, the solutions manual uses delta S = nRlnT2/T1 to solve for change of entropy. Why do they use this formula, because I thought the formula was nClnT2/T1, and C would be 5/2R since it is constant pressure?

AKhanna_3H

In general the subscripts are just indicating volume and pressure. This is similar to saying Cv and Cp as heat capacities at constant volume and constant pressure.

AKhanna_3H

Additionally, if the pressure increases the reaction will shift towards the side of the equation with less moles to counteract the change. If the pressure decreases the reaction will shift towards the side of the equation with more moles.

AKhanna_3H

How would you explain why the cis crystal would have a higher entropy than the trans isomer? Also what does residual entropy mean and is it different than entropy? Thank you!

AKhanna_3H

I had the same question, but I found the answer in an endorsed post from Dr. Lavelle, if you scroll up to the announcements of this section it should be there.

AKhanna_3H

What exactly do we need to know about bomb calorimeters? Is there a specific formula/concept that corresponds to using a bomb calorimeter?

AKhanna_3H

Subscript p refers to constant pressure and subscript v refers to constant volume.

AKhanna_3H

This question would use the heat capacity formula q = nCdeltaT. You would solve for q of copper and q of water by setting them equal to each other and assigning a negative sign to the q of water (calorimeter). You can set them equal to each other because the heat lost by one reaction is gained by th...

AKhanna_3H

I think the book is just using it as an example of any variable to show that delta means "change of." X is a placeholder for other variables such as U.
On page 244 of the textbook it says the symbol delta X means a difference in the property X.

AKhanna_3H

I believe it is because we are assuming an ideal gas, in which there are no intermolecular forces, so we only consider kinetic energy.

AKhanna_3H

Internal energy is represented by delta U. Q represents the heat entering or exiting the system.

AKhanna_3H

I believe it usually depends on the information given. For example, if you are given the bond enthalpies then it would be best to use that method versus a different one.

AKhanna_3H

State functions can be added or subtracted because it does not matter what path it took to get from the initial value to the final value.

AKhanna_3H

How does increasing the pressure affect the reaction? Are reactants or products favored?

AKhanna_3H

pKa + pKb = pKw. Therefore pKa + pKb = 14. 14 - pKb = pKa, and 14 - pKa = pKb.

AKhanna_3H

No, test 1 will cover up to last Friday's lecture (1/17).

AKhanna_3H

Last quarter for 14A with Lavelle, I did all the practice problems on the syllabus for the topics we would be tested on and I found that to be very helpful!

AKhanna_3H

If more reactants are added (increasing the number of moles), the reaction will "shift right" meaning more products will be formed to offset that change. Now that there are more reactants available, more products must form to keep the reaction in equilibrium. If reactants are removed (decr...

AKhanna_3H

There's no study guide, but for 14A with Dr. Lavelle I found it was very helpful to do all the practice problems on the syllabus for the sections we would be tested on. For test 1 I believe those are the first two sections.

AKhanna_3H

Q and K are both measured by the ratio of products over reactants, but K represents that ratio at equilibrium while Q can represent that ratio at any point in the reaction.

AKhanna_3H

I really appreciated that there were a lot of examples and we went through each in detail.

AKhanna_3H

During your week 3 discussion

AKhanna_3H

Le Chatelier's Principle explains how chemical reactions shift to minimize the effects of a change. For example, if more reactants are added, the reaction will shift "right" and more product is formed. If reactants are removed, the reaction will shift "left" and less products wil...

AKhanna_3H

Kc refers to concentrations and Kp refers to pressure, so (aq) would correlate to Kc and (g) to Kp

AKhanna_3H

What room can we pick up our 14A finals from? And can we start getting them this week or next week?

AKhanna_3H

When is the first homework assignment due? I know they are usually due in discussion sections but is that also true for week 1?

AKhanna_3H

Yes the material is cumulative but will focus on material after the midterm.

AKhanna_3H

This question asks whether the following oxides are acidic, basic, or amphoteric: a. BaO b. SO3 c. As2O3 d. Bi2O3
I understand the definitions of acids, bases, and what it means to be amphoteric, but how do you know what each oxide is?

AKhanna_3H

AX4 is for tetrahedral molecules. Square planar molecules have four bonding regions and two sets of lone pairs, or AX4E2.

AKhanna_3H

What email is it? Is there anyway you can send a screenshot because I cannot find that email

AKhanna_3H

Does someone have a screenshot of the table he sent us I can't seem to find it in my email? Thanks!

AKhanna_3H

I believe the exam is cumulative but will emphasize topics after the midterm.

AKhanna_3H

These are the room assignments he posted on his website, hope this helps!

AKhanna_3H

After the review session on Friday!

AKhanna_3H

I think anything from the coordination compounds and acid and base structures on the syllabus should be ok!

AKhanna_3H

The formula gives us (OH2) which indicates aqua, if it was (OH), that would be hydroxido

AKhanna_3H

Besides the 50% required to get a C-, Dr. Lavelle does not determine the grade cutoffs for an A, A-, B+, etc. until after the final, meaning you may not have to get the standard 93% to get an A in the class. It all depends on the overall scores at the end.

AKhanna_3H

Dr. Lavelle explained that the configurations should be written in order of energy level, so 3d would come before 4s.

AKhanna_3H

Since lone pairs count as a region of electron density, I believe they would count towards hybridization. For example, in a water molecule, the oxygen has two lone pairs and two covalent bonds, and would have a hybridization of sp3.

AKhanna_3H

Dr. Lavelle said in a previous post that the seesaw is a topic covered in 14B and we do not need to explicitly know this for the final.

AKhanna_3H

large Ka/small pKa = strong acid
small Ka/large pKa = weak acid

AKhanna_3H

According to a previous post, Dr. Lavelle said that we would not have to calculate one from the other, but it is important to know that when you put an acid in a solution with a pKa less than the pH of the solution the acid will dissociate.

AKhanna_3H

Ba and Br have the highest difference in electronegativity according to periodic table trends, therefore the bonds in BaBr2 are primarily ionic

AKhanna_3H

I believe these are all different names for the same force!

AKhanna_3H

Hydrogen bonds form because hydrogen has a partially positive charge, and hydrogen atoms form hydrogen bonds with extremely electronegative atoms with partially negative charges. These atoms are Fluorine, Oxygen, and Nitrogen.

AKhanna_3H

If I went through the solutions and feel as if I should have received points that I did not get, is there a way to do a regrade request?

AKhanna_3H

Final grades are not assigned until the end of the quarter once the averages are determined. Just try to get as many points as possible throughout the course.

AKhanna_3H

Material after the midterm to what we have learned just before the test

AKhanna_3H

The class is not curved and letter grades are not assigned to tests and midterms. At the end of the quarter Dr. Lavelle will create the cutoffs for A/A-/B+ etc. depending on what the end points are. This means that to get an A in the class you may have to get a different percentage than the standard...

AKhanna_3H

Combustion reactions always have O2 as a reactant and H20 and C02 as products.

AKhanna_3H

Aluminum does not have an expanded octet. Since it is a group 3 atom it sometimes violates the octet rule by having less than 8 valence electrons when bonded.

AKhanna_3H

Since we have not talked about shapes yet in lecture I would say you probably do not have to worry about the shapes of Lewis structures. Once we learn it then you will have to take shape into account.

AKhanna_3H

Na and Cl independently are less stable than when they are bonded because they have incomplete octets as ions. They bond together to achieve a lower energy state and are more stable.

AKhanna_3H

Electronegativity is a measure of the tendency of an atom to form a covalent bond. Fluorine is the most electronegative atom on the periodic table, meaning it has the highest tendency to form a covalent bond. Since Oxygen is close to Fluorine, it also has a relatively high electronegativity. Electro...

AKhanna_3H

Dr. Lavelle said that these are the same thing, just different words for the same concept!

AKhanna_3H

Ions are drawn separated from each other because in ionic bonds, electrons are not shared like in covalent bonds. Rather, electrons are donated or accepted. Therefore, there are no shared electron pairs, and no need to draw single, double, triple bonds between two atoms.

AKhanna_3H

Are the review sessions for the midterm still happening tonight even though classes are cancelled?

AKhanna_3H

The least electronegative atom goes in the center. Electronegativity increases as you go across the periodic table and decreases as you go down the periodic table.

AKhanna_3H

Dr. Lavelle said in lecture that the formal charge of an atom indicates a gain or loss of electrons when forming a covalent bond. Calculating formal charges is helpful in drawing the best possible Lewis structures and making sure that the overall charge of the molecule is represented in the Lewis st...

AKhanna_3H

He started by finding how many valence electrons Sulfur and Oxygen had. Both have 6, and since there are 4 Oxygens present, there are a total of 32 electrons, so your Lewis structure should include 32 electrons. First he drew the diagram with Sulfur in the center and 4 Oxygens each with a single bon...

AKhanna_3H

My TA said that you do not need to know how to do this. I believe he said there is no way to figure it out just from reading a problem, but he definitely said we would not have to do this on a midterm/test. Hope that helps!

AKhanna_3H

The equation for this is on the formula sheet so you don't have to memorize it but you will most likely have to apply it to problems.

AKhanna_3H

You might have to double check, but I believe the tests/midterms/finals are similar to the homework problems which involve calculations, so it is unlikely that you would have to derive an equation on a test. Hope this helps!

AKhanna_3H

A nodal plane by definition is a plane where the probability of finding an electron is 0. This means there are no planes for the s-orbital where the probability of finding an electron is 0.

AKhanna_3H

I think that as long as you understand that +1/2 indicates a positive spin and -1/2 indicates a negative spin for the fourth quantum number, you should be good!

AKhanna_3H

I also believe Dr. Lavelle said that it absorbs all radiation.

AKhanna_3H

Yes it is a constant.

AKhanna_3H

I usually start by figuring out what variables I know and then finding an equation that has the unknown variable in it, filling in all the known variables that apply to that equation.

AKhanna_3H

As an electron gets farther away from the nucleus, the "pull" of the nucleus decreases in strength. Therefore the easier it is for an electron to jump to a higher energy level the farther away from the nucleus it is.

AKhanna_3H

You have to post 5 times by Sunday at 11:59 p.m.

AKhanna_3H

There is no course reader, the only required material is the textbook which also comes with a solution manual.

AKhanna_3H

Could someone please explain how to approach problem M.5? Thanks!

AKhanna_3H

In general, you would use the full number and then round to the correct number of significant figures as the last step of your calculations to get your final answer. For the most accuracy, avoid rounding any numbers in your calculations until the final answer.

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