CHEMISTRY COMMUNITY

DesireBrown1J

For those who already took 14 BL, what advice would you have for the labs? Unfortunately, I will have to do the virtual lab next quarter but I would like to know what was the most useful information from 14A and B that helped you in BL.

DesireBrown1J

Thank you Dr. Lavelle, I really appreciated all the resources you created for this class, such as the workshops and step up sessions. Not many professors take the extra time to provide more resources for students.

DesireBrown1J

Thank you for all your help in chemistry 14A and B. I really appreciate all the hard work you put into making the worksheets and review sessions. They were really helpful.

DesireBrown1J

Deleting the first 50 posts is unnecessary and is tedious. Your TAs will be able to see when the posts were made and will count the 50 that are during this quarter towards your grade. :)

DesireBrown1J

The homework problems at the end of every focus section are the most helpful because they combine lots of topics into 1 problem like the test. (i.e. 4.21, 4.43, 6.43) Would you recommend the ones in sections 5 and 6? Just for clarification which sections were the most helpful related to the Test 2?...

DesireBrown1J

chari_maya 3B wrote:Lyndon's reviews!!

Is his worksheet available now?

DesireBrown1J

I know that Lyndon will have a worksheet for his final review sessions, but are there any other UAs or TAs who do the same? If so, where can I access and print out their worksheets?

DesireBrown1J

One easy way that I remember that the oxidation will be at the anode and reduction at the cathode is through Ox-An (for oxidation-anode). That helped me remember it because it reminded me of the Roxanne song since it sounds like the name. Kinda silly but useful.

DesireBrown1J

Do I have to pay to access Sapling Learning?

DesireBrown1J

How do I access Sapling Learning?

DesireBrown1J

The homework problems at the end of every focus section are the most helpful because they combine lots of topics into 1 problem like the test. (i.e. 4.21, 4.43, 6.43)

DesireBrown1J

Thank you! I didn't realize I made that small mistake!

DesireBrown1J

Why is Cl₂ the oxidizing agent when it actually gains electrons? Shouldn't it be the reducing agent in that case?

DesireBrown1J

Why is n moles of electrons transferred instead of the number of electrons transferred? How do we convert it into moles if they are electrons?

DesireBrown1J

Where in the textbook does it talk about the Nernst Equation? I can't seem to find it.

DesireBrown1J

Does Lyndon have a practice worksheet for Test 2?

DesireBrown1J

This is what I plugged into the equation G = -RTlnK + RTlnQ

delta G=(-(8.314 J*K^-1*mol^-1)(1200K)(ln(6.8))-((8.314J*K^-1*mol^-1)(1200K)(ln(7.38)))

However, my answer was completely off and was not close to the solutions manual.

DesireBrown1J

I am doing the reading for 5G.3: "The Origin of Equilibrium Constants" in Outline 4. It states that the two approaches are kinetics and thermodynamics. We discussed the thermodynamics approach on Friday after the midterm but we did not talk about the kinetics approach. Do we need to know t...

DesireBrown1J

My final answer was pOH=12.5. Is that correct (for those who got full points)?

DesireBrown1J

(a) Calculate the heat that must be supplied to a copper kettle of mass 400.0 g containing 300.0 g of water to raise its temperature from 20.0 C to the boiling point of water, 100.0 C. (b) What percentage of the heat is used to raise the temperature of the water? (See Table 4A.2.) How do I solve th...

DesireBrown1J

For which problems on the equation sheet will we ever use R=8.314*10^-2 L*bar*K^-1*mol^-1?

DesireBrown1J

On page 251, the textbook says "The heat capacity of a sample of a substance is calculated from its mass and its specific heat capacity by using C=m*C s ". I'm confused on what exactly the book is trying to say with this because mass cancels out anyways in this equation since C s =C/m. C=m...

DesireBrown1J

There are other types of work but we only need to worry about expansion work for the midterm. Here is a table of other types of work that was in the textbook on page 245.

types of work.JPG

DesireBrown1J

Cavalli_1H wrote:hess's law can also be applicable to gibbs free energy for the reason of it being a state property

How is it explained and applied to Gibbs free energy?

DesireBrown1J

Why is delta H always q but q is not always delta H? What exactly does he mean by that?

DesireBrown1J

What was the little saying to remember the state functions other than entropy and enthalpy? The HUGS and TV one?

DesireBrown1J

Where exactly in the textbook does it talk about isobaric reversible reactions?

DesireBrown1J

I know that Lyndon usually posts a practice worksheet for his midterm/final review sessions and he often names it after some type of food (such as marshmallow for his Chem 14a final review session). Has he posted the review worksheet for his review session next week?

DesireBrown1J

Where in the textbook do they talk about degeneracy and which homework problems are related to it?

DesireBrown1J

Just to clarify, all biological systems are closed systems?

DesireBrown1J

The equation for change in entropy is delta(S)=q rev /T. As temperature increases, the change in entropy will decrease because temperature is in the denominator. Exothermic and endothermic have to do with changes in temperature but in this case, temperature is remaining constant (from what I underst...

DesireBrown1J

Jeremy_Guiman2E wrote:You do use w = P * A * D!

w = 2 atm * (0.015 m)² * 0.2 m * pi
w = 2.8274 * 10^-4 m³ * atm

Then, you can multiply the answer by 101,325 Pa to convert from atm to Pa. Once you have your answer in m³ * Pa, it is equal to that amount in joules (J).

Where did you get 0.015m from and pi from?

DesireBrown1J

I see that everyone is saying C is either a closed or isolated system. For clarification, the textbook solutions states that it is an isolated system. It's an isolated system because nothing is being exchanged with the environment in the bomb calorimeter. In a closed system, energy can be exchanged ...

DesireBrown1J

You need to make an ice table for the reaction of NH3 reacting with H2O. Once you solve for the equilibrium concentration of OH-, you can find pOH (pOH= -log[OH-]). Then you can convert pOH to pH (pH + pOH = 14). Percentage protonation is calculated by doing ([NH4+]/[NH3]initial) x100% How are we s...

DesireBrown1J

A researcher fills a 1.00 L reaction vessel with 1.84 x 10 -4 mol of BrCl gas and heats it to 500 K. At equilibrium, only 18.3 % of the BrCl gas remains. Calculate the equilibrium constant, assuming the following reaction is taking place. 2BrCl(g) ⇌ Br2 (g) + Cl2(g) A. 19.5 B. 8.39 x 10-5 C. 4.98 D....

DesireBrown1J

18. You are studying the following unbalanced reaction at high temperatures: NH3 (g) ⇌ N2 (g) + H2 (g) In one of your experiments at 500K the measured partial pressures are: NH3 0.887 bar H2 0.168 bar N2 0.0561 bar a) Determine the equilibrium constant for this reaction at 500 K. A. K = 3.38 x 10-4 ...

DesireBrown1J

Although there is no practice test or study review for Test 1, I highly recommend completing all of the homework problems to make sure you can answer and understand all of them and make sure you can explain all the concepts in the outlines. I also recommend going to UA sessions because they provide ...

DesireBrown1J

I was wondering about this too. The book gives 3.2 x 10^-12 as the answer because it multiplies 3.1 by 10^-3, which I think implies that it has something to do with units. However, the units of 3.1 are mol*L^-1, which are the same units the values in the other parts had and those values weren't mul...

DesireBrown1J

I used (1.0 x 10^-14)/3.1 but my answer was also 3.2 x 10^-15. Also, when I multiplied 3.1 with 3.2 x 10^-15 to see if my calculations are correct, I get 1.0 x 10^-14.

DesireBrown1J

You do not have to convert them to partial pressure. You can use Kc=[R]/[P] to solve for this problem by plugging in Kc from the Table 5G.2 and [HI] is 2.21 x 10^-3 mol/L and [I2] is 1.46 x 10^-3 mol/L to solve for the equilibrium molar concentration of H2. If you completed 5I.1, it follows the same...

DesireBrown1J

Do sig figs matter in this one? I did 3 sig figs for the equilibrium molar concentration because Kc had 3 sig figs, yet the solutions manual answer was in 2 sig figs.

DesireBrown1J

Yes, K_P applies to gases with partial pressures and K_C is for aqueous solutions or gases with molar concentration.

DesireBrown1J

I am confused because today I was supposed to have my discussion at 9am with TA Kevin Chandler in Rolfe 3134 because that's on the study list and on the office hours sheet I printed out in the beginning of this week. Yet, when I walked in the classroom, it was a different TA, a woman, and I assumed ...

DesireBrown1J

PO2/PO3 will be different because the ratio of the reactant to the product is different at equilibrium point for different amounts of starting reactant. Only (PO2)^3/(PO3)^2 or (PO3)^2/(PO2)^3 are guaranteed to be the same because they are the equilibrium constant and the inverse of it. For c, woul...

DesireBrown1J

What exactly is the ideal gas constant in R? When I looked it up, I realized that there are two different ones to use. How do we determine which one to use based on what information is given to us in a problem?

DesireBrown1J

I wrote my answer for part a as K=[C 2 H 4 Cl 2 ] 2 [H 2 O] 2 /[C 2 H 4 ] 2 [O 2 ][HCl] 4 but the textbook has it in terms of partial pressures because they are gases. This is also how we had to write it when doing the modules. If I do not write it in terms of partial pressures on the exams or homew...

DesireBrown1J

Will we have the same TAs for next quarter for the most part? If so, is there a list of which TAs are teaching the discussion sections?

DesireBrown1J

I got the correct answers for all the parts in 6A.3, yet I wanted to double check to make sure my chemical equations for the proton transfer equilibria were correct because that wasn't in the solutions manual. a) H 2 SO 4 + H 2 O <-> H 3 O + + HSO 4 - b) C 6 H 5 NH 3 + + H 2 O <-> H 3 O + + C 6 H 5...

DesireBrown1J

Look at which ones have the higher electronegativity difference on a central atom and which ones have more oxygens attached to the central atom.

DesireBrown1J

If a molecule has more H atoms compared to another molecule with fewer H atoms, would the one with more H atoms be considered a weaker acid because it is less likely that it will be completely deprotonated?

DesireBrown1J

So, a greater electronegativity means that the acid is stronger?

DesireBrown1J

So, electron-withdrawing leads to the release of H+ ions because cations has high electron-withdrawing and pull the electrons towards it, which then results in the release of H+ to form H₃O+? And all this makes it an acid?

DesireBrown1J

For this problem, how do we write the net ionic equations for I^- to cancel out?

DesireBrown1J

Can someone explain to me what I did wrong for this problem?

a) M=0.025 mol HCl/0.200 L =0.125 mol*L^-1
pH=-log(0.125)=0.903?
But the solutions manual says 1.6

DesireBrown1J

The chemical equation is not balanced(The I2 should be just I^-(aq)). After correcting this, writing the net ionic equation, the I^- ions will cancel out and the species left are NH4+,H2O,H3O^+,NH3. Since the proton donator is NH4+, NH4+ is the bronsted acid. Why would it be NH 4 + as the acid inst...

DesireBrown1J

Do we need to know about the Arrhenius acids and bases? I saw it in the textbook but I do not remember him mentioning it in class.

DesireBrown1J

Does anyone have any good tips and tricks for memorizing certain things for the exam? Such as the naming for coordination compounds

DesireBrown1J

I got the correct answers for all the parts in 6A.3, yet I wanted to double check to make sure my chemical equations for the proton transfer equilibria were correct because that wasn't in the solutions manual. a) H 2 SO 4 + H 2 O <-> H 3 O + + HSO 4 - b) C 6 H 5 NH 3 + + H 2 O <-> H 3 O + + C 6 H 5 ...

DesireBrown1J

I do not think the TAs will have enough time to grade them and give them back to us before Thanksgiving break. So, we should get them back during our week 10 discussions. I would email your TA and see what they will be doing.

DesireBrown1J

A dipole-dipole intermolecular interaction occurs between two polar molecules.

DesireBrown1J

The VSEPR formula for pentagonal bipyramidal is AX₇.

DesireBrown1J

I know that for the exam, the problems will probably be more advanced than those on the homework. Does anyone have any more additional practice problems for sigma and pi bonds?

DesireBrown1J

I would also recommend doing homework problems from 3F because intermolecular forces will also be on the exam.

DesireBrown1J

2E.19, Part B

So if we do get a molecule like (CH₃)₂Be on the test or final, would we have to say it is tetrahedral about the carbon atoms, since there is not an exact shape we learned to accurately represent the whole molecule?

DesireBrown1J

I would recommend making flashcards on the 12 different shapes and also adding the bond angles, VSEPR formula, name, examples, and a drawing. That has been helping me remember them and also color-coding everything in the drawings.

DesireBrown1J

This photo is from the textbook of all the shapes we should know for test 2.

[img]

Screenshot%202019-11-16%2017.24.28.png

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DesireBrown1J

So, the bond angle in H₂O is 104.5 degrees (from the textbook). On test 2, should we state that the bond angle for all angular molecules is 104.5 degrees or should we just say less than 120 degrees?

DesireBrown1J

Kaitlyn Jang 1F wrote:Only if hybridization is also on the one page of notes he has left to teach us on Monday

I thought I heard Lavelle state in lecture that there will not be any hybridization on Test 2. Did anyone else hear the same or did I hear it wrong?

DesireBrown1J

If a central atom has more lone pairs, would that affect its bond lengths with the surrounding atoms?

DesireBrown1J

What is an example of a question where we would use the interaction potential energy equation? Are you talking about this one introduced in the beginning of 3F.1? I was not sure about that one because there are no homework problems related to that question and it is not on the constants and equatio...

DesireBrown1J

Do the lone pairs of the noncentral/surrounding atoms affect the shape and angles of the overall molecule? If so, how do they change the shape?

DesireBrown1J

There is also another way you could solve the problem. In order to determine how many grams of glucose is left over, you would first need to determine how many grams of water the 10.0g of glucose produces. You would convert the grams of glucose that was initially present into moles. Then, you would...

DesireBrown1J

So for the moles of O₂ initially present, did everyone get about 0.28 moles of O₂?

DesireBrown1J

Does anyone have some creative tips for memorizing certain things that are not on the constants and equation sheets?

DesireBrown1J

The homework question reads "Compounds having bonds with a high covalent character tend to be less soluble in water than similar compounds that have low covalent character. Use electronegativities to predict which of the following compounds is the more soluble in water". I know that we wou...

DesireBrown1J

So when you calculate the dipole moment (charge * bond length), would the arrow representing the dipole always be pointed towards the δ^- or are they any exceptions to that?

DesireBrown1J

So, work function is essentially the same as threshold energy?

DesireBrown1J

Phosphorus actually has 5 valence electrons because its electron configuration is [Ne]3s²3p³. 3s²3p³ are the outermost orbitals and have the highest energy levels, which make the electrons in here the valence electrons.

DesireBrown1J

As effective nuclear charge increases, atomic radius decreases and ionization energy increases.

DesireBrown1J

Is the ground state electron configuration for Cu=[Ar]3d¹⁰4s¹ and Cr=[Ar]3d⁵4s¹?

DesireBrown1J

Flourine has the highest electronegativity because noble gases have no electronegativity. They already have a full outer shell, so they will not gain nor lose an electron.

DesireBrown1J

When writing the electron configuration, why is it 3d instead of 4d? I was assuming that it would be 4d because it is in the 4th period.

Example: Ge=[Ar]3d¹⁰4s²4p³ instead of Ge=[Ar]4d¹⁰4s²4p³

DesireBrown1J

For problem 1F.1 states "Arrange the elements in each of the following sets in order of decreasing atomic radius: (a) sulfur, chlorine, silicon; (b) cobalt, titanium, chromium; (c) zinc, mercury, cadmium; (d) antimony, bismuth, phosphorus". I used appendix 2D to find the atomic radii and a...

DesireBrown1J

In one of the UA sessions that I went to today, the UA told us to write Cr as [Ar]3d⁵4s¹ instead of [Ar]4s¹3d⁵. I do not know why he said that but can someone better explain this to me?

DesireBrown1J

What are some practice problems from the book that require us to use the work function equation hv-Φ=1/2mv²?

DesireBrown1J

I know that a few students bought the e-textbook instead of the regular textbook. I'm interested in buying that one instead but I don't know which bundle on the Macmillan Learning student store includes the e-textbook. Do all of them include the e-textbook or only specific bundles? Loose-Leaf Versio...

DesireBrown1J

AlyssaYeh_1C wrote:When doing your calculation, the Δv you should use is 10m/s, which is your maximum uncertainty.

Why do we have to use the maximum uncertainty velocity in the Heisenberg Indeterminacy equation?

DesireBrown1J

Would we be able to go to office hours and review our test with a TA for any problems we got incorrect?

DesireBrown1J

If someone was able to complete the Angstrom question, can you please explain to me (step by step) how to solve the problem?

DesireBrown1J

The question states "What is the velocity of a neutron of wavelength 100. pm?". I know that DeBroglie's equation has to be changed to find v and we have the wavelength and Planck's constant. However, how do we find the mass for 1 neutron? Are we supposed to know that from high school chem?

DesireBrown1J

Did we go over the Indeterminacy equation in class on Friday? I see that I wrote it down as a fundamental equation for Quantum mechanics but I only remember discussing and taking notes on De Broglie's wave equation.

DesireBrown1J

Maya Serota 3G wrote:The actual value will be given to you in the question. From there the equation for percent yield is (theoretical/actual) x 100.

Sorry, but the percent yield would be the actual amount over the theoretical amount. So, (actual yield/theoretical yield)x100%.

DesireBrown1J

For this homework problem, the given wavelength is in nm. Should we covert all the wavelengths we need to find to nm? We are also given two different frequencies, one in Hz and one in MHz. Should the answers for the other two frequencies be in Hz or MHz?

DesireBrown1J

For the week 2 homework, should we only be doing the problems from the Quantum World section? I just wanted to make sure before getting started on it.

DesireBrown1J

The periodic table is color coded and it will indicate whether an element is a liquid, solid, or gas. I am not sure how to figure out if it is aqueous.

DesireBrown1J

You can only change the number of moles in the equation to balance it.

DesireBrown1J

He wants us to have our name, UID, and our section on the top corner of the paper. I put it on each paper just in case they come apart from the staple.

DesireBrown1J

In some homework problems, reactant/products are sometimes formatted like Mg(N₃)₂(s). How should I be interpreting problems like this in order to balance them correctly? Should I see it as equal to MgN₆(s) or Mg₂N₆(s) or some other way?

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