CHEMISTRY COMMUNITY

Donna Nguyen 2L

How does a catalyst affect (a) the rate of the reverse reaction; (b) the value of ΔH° for the reaction?

I know how to answer part A, but I'm unsure how to answer part B. What does a catalyst contribute to the value of ΔH°?

Donna Nguyen 2L

It would be included!

Donna Nguyen 2L

I'm sure having 100 posts is fine :)

Donna Nguyen 2L

Yes, on Dr. Lavelle's website, he has a link called "Final Exam: Review Sessions and Exam Venues," and it seems that the review session will be this Friday.

Donna Nguyen 2L

The rate constant of the reaction between CO2 and OH− in aqueous solution to give the HCO3− ion is 1.5*10^10 L*mol^-1*s^-1 at 25°C. Determine the rate constant at human body temperature (37°C), given that the activation energy for the reaction is 38 kJ*mol^-1. I'm confused about the solution in the ...

Donna Nguyen 2L

To add on, water would be included in the gas phase but not as a solid or liquid since solids and liquids aren't included when calculating equilibrium constants since the molar concentration wouldn't change.

Donna Nguyen 2L

I assume what everyone else is saying, about 7-10 questions.

Donna Nguyen 2L

It will cover the second page of outline 4 and all of outline 5.

Donna Nguyen 2L

It covers things on the second page of outline 4, and all of outline 5.

Donna Nguyen 2L

I feel like either is fine, but I think I would do electrochemistry since our test is this week!

Donna Nguyen 2L

Essentially, it covers material that we learned post-midterm up until Monday's lecture, which is the second page of outline 4 and all of outline 5.

Donna Nguyen 2L

I don't think there are any extra credit opportunities unfortunately but it would be super helpful.

Donna Nguyen 2L

I'd suggest something on electrochemistry since we just finished learning it and since it is covered on test 2.

Donna Nguyen 2L

Dr. Lavelle's website says that test 2 will cover the second page of Outline 4: Thermodynamics and Outline 5: Electrochemistry and its Applications.

Donna Nguyen 2L

I think the Organic Chemistry tutor definitely helps me understand some concepts better, but like someone else commented, he probably doesn't cover everything we learn in lecture.

Donna Nguyen 2L

I think you can also pick up your midterm during your discussion section if you aren't able to pick it up after class on Wednesday.

Donna Nguyen 2L

How does delta G tell us which way a reaction will shift?

Donna Nguyen 2L

I definitely feel the same way. I felt like I studied super hard for the midterm and I thought that I was (kind of) ready, but it was more difficult than I hoped and expected. I feel like the best way to better prepare for these types of questions is to continue doing practice problems and understan...

Donna Nguyen 2L

I believe it will be material learned post-midterm up until the week of the test or so because I remember Dr. Lavelle doing something similar last quarter for 14A. But I agree, check with your TA to be sure!

Donna Nguyen 2L

Since Dr. Lavelle covered the rest of thermodynamics (focus 5G.3 5G.4, and 5J.3) and the beginning of electrochemistry on Friday, I think we can still turn in work on these topics since they are recently covered material.

Donna Nguyen 2L

What's the relationship between ∆G, ∆H, and ∆S? I know that the Gibbs Free Energy equation is ∆G = ∆H - T∆S, but I'm not sure how exactly it all fits together.

Donna Nguyen 2L

In many of our examples and homework problems, the R constant is 8.314 J/mol·K, but if you look at Dr. Lavelle's constants and equations sheet, R is the gas constant and actually has different values. The R value you use depends on the units that are given in the problem.

Donna Nguyen 2L

I believe that Cp = (5/2) R applies to diatomic and polyatomic gases, while Cv = (3/2) R applies to monoatomic gases.

Donna Nguyen 2L

How does Gibbs Free Energy relate to spontaneity?

Donna Nguyen 2L

It generally depends on what units are given to you in the problem, then you base which R to use off of that.

Donna Nguyen 2L

Like everyone else is saying, the UAs put together a review sheet/study guide but Dr. Lavelle himself doesn't give any out.

Donna Nguyen 2L

I also got my test back in my discussion section.

Donna Nguyen 2L

He unfortunately doesn't post slides.

Donna Nguyen 2L

It's cumulative so it will cover the topics from Test 1 + Thermochemistry and Thermodynamics.

Donna Nguyen 2L

My TA told me that the answer key won't be posted, but if you need help with a specific question, I'm sure your TA can help you with it.

Donna Nguyen 2L

I was also looking for the solutions, but I don't think they're posted anywhere.

Donna Nguyen 2L

Yes, I think homework is on outline 3 (thermochemistry).

Donna Nguyen 2L

Yes, partial credit is given so it's important to always show all of your work even if your final answer turns out to be incorrect.

Donna Nguyen 2L

Dr. Lavelle himself doesn't give out practice tests but there are some on Chemistry Community that were posted by UAs.

Donna Nguyen 2L

Ellen Amico 2L wrote:We have to pick them up ourselves in Young Hall 3034 between 9-5pm.

Also, I think they're closed from 12PM-1PM (no one was there at the time when I tried picking it up at 12:30).

Donna Nguyen 2L

Yes, I believe homework is still due.

Donna Nguyen 2L

Test 1 covers Equilibrium and Acid & Base Equilibria, so topics such as Le Chatelier's Principle, Q/K, calculating pH/pOH, etc.

Donna Nguyen 2L

The midterm and final are cumulative and the tests cover certain outlines, as shown on Dr. Lavelle's class website.

Donna Nguyen 2L

It begins this week (week 3) in your discussion section and covers Equilibrium and Acid & Base Equilibria.

Donna Nguyen 2L

The test is during your discussion section and covers Equilibrium and Acid & Base Equilibria.

Donna Nguyen 2L

I was having the same problem! It's probably just a mistake in the solutions manual.

Donna Nguyen 2L

Why are units omitted when calculating K?

Donna Nguyen 2L

I'm sure it's fine since it's still recently covered material!

Donna Nguyen 2L

You use 0.0189 instead of 0.0424 since this value is larger than the concentration of NO2.

Donna Nguyen 2L

I think we should include the ICE charts since Dr. Lavelle did an example with it in class, and it may also be a way to receive partial points.

Donna Nguyen 2L

What's the difference between Q and K? Or, how are they similar?

Donna Nguyen 2L

What happens if K is small and what happens if K is large?

Donna Nguyen 2L

Can someone explain 5H.1? 5H.1 is similar to the example shown on page 410 of the textbook, so you can follow that when trying to do this homework problem. In fact, part (a) is almost the same as the example. With the reverse reaction, the equilibrium constant is the reciprocal of the original chem...

Donna Nguyen 2L

Why are solids and liquids not included in the K expression?

Donna Nguyen 2L

Is there a difference between Kc and K? I couldn't figure out if there was a difference or not in the textbook.

Donna Nguyen 2L

The final is cumulative so it will cover material we learned since week 1.

Donna Nguyen 2L

I think it depends on your TA. For me, my points aren't posted yet.

Donna Nguyen 2L

The grades are posted on myUCLA!

Donna Nguyen 2L

I assume calculators will be allowed.

Donna Nguyen 2L

His syllabus says the class doesn't use a curve, but I've heard that it depends on the grades distribution at the end of the quarter.

Donna Nguyen 2L

The final is cumulative, so it covers all material from week 1 to week 10.

Donna Nguyen 2L

I don't know if we're going to have a review lecture like for the midterm, but I don't think that we will learn on the last day of lecture, considering our final is two days after that day.

Donna Nguyen 2L

I totally get you, but I hear that the step up sessions are really helpful!

Donna Nguyen 2L

What's the difference between a sigma bond and a pi bond?

Donna Nguyen 2L

What is week 9 homework on?

Donna Nguyen 2L

I think I remember my TA saying that test 2 will be the same length as test 1.

Donna Nguyen 2L

I think I remember my TA saying that it's going to have 7 or 8 questions like test 1.

Donna Nguyen 2L

Since there's no lone pairs, I don't think it's necessary to include the E.

Donna Nguyen 2L

What is the AXE notation? What does each letter represent?

Donna Nguyen 2L

I've heard the same, and I've also heard that 14BL takes up a lot of time and it's really hard to manage while taking 14B simultaneously, apparently.

Donna Nguyen 2L

I don't think Dr. Lavelle has announced what will be on test 2 yet, but I'm going to guess that it will be on the sections Chemical Bonds and Molecular Shape and Structure.

Donna Nguyen 2L

I feel like he won't post more only because the last videos were from the early quantum unit, but I agree that it would be super helpful if he did.

Donna Nguyen 2L

I'm going to do more practice problems. I hear that the step-up sessions are really helpful, so I might start going to those as well.

Donna Nguyen 2L

Why are the elements H, He, Li, and Be exceptions to the octet rule?

Donna Nguyen 2L

How do you calculate formal charge? What's the equation and what does everything stand for?

Donna Nguyen 2L

I think either is fine to use, but I would recommend using the one on the constants and equations sheet just in case.

Donna Nguyen 2L

Yes, I believe that we will be given the formula sheet and the periodic table.

Donna Nguyen 2L

Hertz is the unit for frequency. Hertz is also the same as (s^-1), so both units are interchangeable for frequency.

Donna Nguyen 2L

I would assume that we won't need to know it for all types except for visible light.

Donna Nguyen 2L

Like everyone said, the conversion sheet will be given, but there may be some conversions that aren't on there that may be helpful to memorize anyways.

Donna Nguyen 2L

Homework for week 5 should be on chemical bonds since we recently learned this.

Donna Nguyen 2L

What's the difference between ionic and covalent bonds? Which one is stronger?

Donna Nguyen 2L

Dr. Lavelle posted all of the information about the midterm on his website so check that out if you haven't yet.

Donna Nguyen 2L

I think homework for week 5 should be on chemical bonds since it was the most recently discussed material in lecture.

Donna Nguyen 2L

It is due Sunday night at 11:59PM. My TA said that even if you post at 12, the computer will count it towards next week.

Donna Nguyen 2L

keV is the abbreviation for kiloelectron volts, a unit of energy. This is equal to 1000 eV (electron volts). 1 eV is equal to 1.602*10^-19 J, which is also a constant we have seen before for energy.

Donna Nguyen 2L

This is the set mass of the electron so it doesn't change.

Donna Nguyen 2L

How many orbitals can have the following quantum numbers in an atom: (a) n=2, l=1; (b) n=4, l =2, ml=-2; (c) n=2; (d) n=3, l=2, ml=+1?

How would I approach this problem?

Donna Nguyen 2L

Both are correct. 2.998*10^8 m/s is more accurate, but I'm sure you can use 3.0*10^8 m/s as well, as it also gives an accurate answer.

Donna Nguyen 2L

I think homework for this week is based on the quantum world since we're still on it.

Donna Nguyen 2L

Most of the time, these constants and equations will be provided (correct me if I'm wrong), but I believe it'll be helpful to remember Planck's Constant, the speed of light, and the formula E=hv.

Donna Nguyen 2L

We probably don't need to memorize the masses. If anything, I think we would need to know the mass of an electron since it seems to be the most commonly used, but I don't think we'll need to memorize it.

Donna Nguyen 2L

The formula for momentum is p(momentum) = mass * velocity. Momentum is the quantity of motion that an object has, and it takes into account mass and velocity, while velocity is the rate of change of the position of an object.

Donna Nguyen 2L

Like someone said above, the equations should be given, but it's still helpful to have them memorized.

Donna Nguyen 2L

The unit for wavelength is meters. Although, it can be seen in nanometers, kilometers, picometers, etc.

Donna Nguyen 2L

I think we can do our homework in either pen or pencil, but pen will probably make it easier to read and therefore easier to grade.

Donna Nguyen 2L

Adding on, the test covers all the fundamentals and reflects the homework that we have been doing (review of chemical & physical principles).

Donna Nguyen 2L

I don't think you will need to rearrange the question. Dr. Lavelle probably does it for easier viewing and to let us see how he got to that point.

Donna Nguyen 2L

I believe that it is correct to leave your answer in pm, but convert if the question asks you to convert.

Donna Nguyen 2L

I remember my TA saying it will be provided on the test so we won't have to memorize it.

Donna Nguyen 2L

I don't remember what my TA said, but I suggest knowing sig figs anyways because it'll probably be needed in future exams.

Donna Nguyen 2L

I remember the site taking me to some page that told me whether I was ready for Chem 14A or not. Don't worry, I'm also rusty on high school chem, especially since it has been 3 years since taking it. We're all on the same page!

Donna Nguyen 2L

For homework 2, I think we can choose from the fundamentals section, but assuming that Dr. Lavelle will teach the quantum world, we should choose homework problems from that section.

Donna Nguyen 2L

I think you should try to show as much work as possible because whoever is grading might want to see the steps in how you approach the problem and get the answer.

Donna Nguyen 2L

I put my name, discussion section, and UID in the top right corner of the page and clearly wrote out the problem number and boxed my answers. Hopefully that's all we need to put.

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