CHEMISTRY COMMUNITY

Lizette Noriega 1H

Hi,
Is the rate-determining step the same as the slow step? Does this reaction ultimately define our rate?

Lizette Noriega 1H

Hello,

Can someone clarify the ideas behind the pre-equilibrium approach and explain when it is necessary to use this method? Thanks.

Lizette Noriega 1H

Hello,

What is the difference between a fast and slow step reaction? What does this information tell us with regard to solving problems?

Lizette Noriega 1H

Hello,

Does anybody know if Test 2 will become available for pick up anytime soon?

Lizette Noriega 1H

An intermediate is produced in the first step then later consumed in the second step while the catalyst is consumed in the first step then produced in the second.

Lizette Noriega 1H

Letty Liu 2C wrote:I think it depends on what information you're given, so what you're working with. I believe there is only two versions of the Nernst equation though: one with lnQ and one with logQ.

Got it! But when do we use lnQ rather than logQ and vice versa?

Lizette Noriega 1H

I have a question about the following problem: Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 M Ni(NO3)2(aq). In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH 5 11.0 at 298 K. See Table 6I.1. How do...

Lizette Noriega 1H

Qiu Ya Wu 4I wrote:We use platinum and graphite as the electrode in our cell diagrams when there are no conducting solids present for the given half-reaction.

But what is the difference between the two? How do you know when to use one over the other?

Lizette Noriega 1H

I've seen the different versions of the Nernst equation but when do we know whether to apply one of the other?

Lizette Noriega 1H

When do we know to use Pt(s) or C(gr) as our solid in cell diagrams?

Lizette Noriega 1H

positive cell potential (-E) = negative delta G = spontaneous
negative cell potential (+E) = positive delta G = nonspontaneous

Lizette Noriega 1H

The absence of a solid in your reaction would require the use of platinum as an electrode. As mentioned above, the fact that it is a good conductor will prevent it from interfering with the reaction.

Lizette Noriega 1H

Will Test 2 have any overlapping topics from the midterm? Or will it only cover topics from the midterm up until now?

Lizette Noriega 1H

Does it matter which side you place the reduced reaction and the oxidized reaction? I've come across multiple sources that switch the orientation of the anode and cathodes so I could use some clarification on that. Thanks!

Lizette Noriega 1H

The procedure is the same but the basic solution requires you to use OH- instead of H+

Lizette Noriega 1H

My TA was informing us that the standard order for the elements in the cell diagram goes as following: solid|gas|aqueous || aqueous|gas|solid But it would be difficult to establish their phase accordingly. The question should provide you with any information you need while keeping in mind that one l...

Lizette Noriega 1H

According to Lavelle's website, Test 2 will cover the 2nd page of Thermodynamics (see Outline) and Electrochemistry

Lizette Noriega 1H

You can use Pt (s) if there is an absence of a solid in a redox reaction; because it is an inert conductor, it will allow for the transfer of electrons without interfering with the reaction itself

Lizette Noriega 1H

A positive cell potential (E) will result in a negative delta G (via the equation delta G = -nFE), thus creating a spontaneous reaction. Similarly, a negative cell potential will result in a positive delta G, creating a nonspontaneous reaction

Lizette Noriega 1H

Hello,
I just need clarification on the function of the salt bridge. Is its purpose to neutralize the charge build-up within the galvanic cell?

Lizette Noriega 1H

It's entirely up to the TA- some will require you to submit 5 posts per week while others are fine with a total of 50 posts by the end of the quarter

Lizette Noriega 1H

My TA told us that 4I.9 was the homework question used on that exam

Lizette Noriega 1H

The status of the system helps you recognize the presence/absence of exchange in energy and matter, thus allowing you to understand the relationship between the system and its surroundings (and helps you solve the problems given).

Lizette Noriega 1H

As mentioned above, the units for heat capacity should be Joules/Celcius (J/°C) but if given kilojoules (kJ), this should be an acceptable answer as well unless the question specifically asks for joules, in which you would have to convert from kilojoules to joules.

Lizette Noriega 1H

If you were to reverse a reaction, the value for the constant will be the inverse (1/Kc) whereas if you multiply the reaction by some constant, the value of Kc will have to be raised by the same value (Kc^x).

Lizette Noriega 1H

As everyone else has mentioned, there is no score distribution but you should ask your TA about your class average.

Lizette Noriega 1H

You can check out Lyndon's review worksheet which will be posted tonight around 7 pm. He will be hosting a review session to go over the problems on Sunday.

Lizette Noriega 1H

Yes, the midterm will be cumulative, covering the topics from equilibrium to thermodynamics

Lizette Noriega 1H

Are these biological examples going to be on the midterm?

Lizette Noriega 1H

Isothermal means there is a constant temperature present in the system, therefore, the most ideal equations to use would be the ones that include a change in volume or pressure

Lizette Noriega 1H

Hello,

In today's lecture, Lavelle mentioned having extra resources to review on calculus. Can these be found on his website?

Thanks!

Lizette Noriega 1H

Unfortunately, there are no extra credit opportunities for this class. Make sure to try your best and study hard!

Lizette Noriega 1H

Unlike heat and work functions, they are dependent on the path taken in order to reach the endpoint

Lizette Noriega 1H

Yes, they must be on opposite sides and they have to be balanced in order to cancel them out

Lizette Noriega 1H

Based off of Lavelle's class announcements, I believe it will cover all the topics we have discussed until now, finishing with thermodynamics. You can use the class outlines to guide your studying as Lavelle has mentioned that the material is based on the objectives

Lizette Noriega 1H

Does anyone know if the final exams are available after Week 3? If so, where can we find them?

Lizette Noriega 1H

I would definitely recommend the UA sessions. For extra practice and better understanding, I would recommend "The Organic Chemistry Tutor" on Youtube because he explains concepts in addition to working through examples. Overall, try to stay on track with the homework and understand them as...

Lizette Noriega 1H

It is the proton transfer between two of the same molecules

Lizette Noriega 1H

Can anyone explain how they solved the following question (#7 from the UA Practice Exam Worksheet)? Thanks!

"A basic aqueous reaction initially had 0.057 M NH3. At equilibrium the concentration of hydroxides was 1.0x10^-3. Write out the equation and find the percent protonated."

Lizette Noriega 1H

You would set up an ice table. Initial concentrations: 1 for H2, 2 for Cl2, and 0 for HCl. We don't know how much the change is, so we represent this with -x, -x, and +2x, respectively. Therefore, the expressions for the equilibrium are: H2 = 1-x, Cl2 = 2-x, and HCl = 4x^2. Write the expression for...

Lizette Noriega 1H

Can someone explain their process for #6? Thanks!

Lizette Noriega 1H

If the problem doesn't specify, either should be fine to use. Although, if you are given concentrations then you are likely to use Kc rather than Kp, or if the problem mentions a gas, you would use Kp for partial pressure

Lizette Noriega 1H

I don't believe so but it's useful to rely on the learning outcomes and base your studying on the areas you need the most practice on

Lizette Noriega 1H

Is temperature the only factor that influences K? Also, which factors influence the reaction quotient?

Lizette Noriega 1H

Just curious, do you know if we'll need to know certain biological examples for future exams?

Lizette Noriega 1H

I'm still a bit confused when it comes to ICE tables. What are certain indicators of a problem that lets us know we'll need an ICE table to solve it?

Lizette Noriega 1H

Is the homework for this week due tomorrow (Friday) in lecture or in discussion next week?

Lizette Noriega 1H

R is the gas constant but it can use different units such as torr, atm, or bar

Lizette Noriega 1H

Megan Kirschner wrote:What exactly is the difference between Kc and Kp? I know (or think) they are equilibria constants but what do they individually represent?

Kc is used for the concentration of aqueous solutions and gases while Kp is for the partial pressures of gases

Lizette Noriega 1H

Can someone explain the concept behind Q? When is it essential?

Lizette Noriega 1H

Can someone clarify the following for me? Are these the correct uses for Kc and Kp?

Kc = concentration of gases
Kp = partial pressures

Lizette Noriega 1H

Why doesn't K have any units?

Lizette Noriega 1H

Wednesday's lecture placed emphasis on Chem 14B and introduced us to the topics we will learn in that class. I don't believe we have to know anything in particular from that lecture for the final

Lizette Noriega 1H

How would you figure out the shape of the following coordinate compound?

[Cr(NH3)3Cl3]

Lizette Noriega 1H

I would suggest looking at the examples mentioned above plus acid rain (not for coordination compounds but it is a real-life example that has come up throughout UA worksheets)

Lizette Noriega 1H

-ate is added to the end of the metal name when there is an overall negative charge to the complex

Lizette Noriega 1H

Avoiding any last-minute cramming and getting a good night's sleep is always a good idea before exams

Lizette Noriega 1H

The syllabus states, "50% or higher is required to pass with a C- or higher". Does this mean you need 250 out of the 500 points to pass the class with a C-?

Lizette Noriega 1H

I don't believe it will be on the test but Dr.Lavelle draws the structures in class in order to help us better understand the concept. Drawing the Lewis structures can only benefit you but it is not required

Lizette Noriega 1H

They do not influence molecular structure because each bond is considered to be one region of electron density, despite the single/double/triple bonds that can be present

Lizette Noriega 1H

If the complex is an anion/contains a negative charge, you at the -ate to the end of the transition metal

Lizette Noriega 1H

They are interchangeable terms but using one over the other is to indicate the presence of the lone pair on the oxygen. Usually, H2O is written on the left and OH2 is on the right in order to accommodate for the bond that exists between the lone pair of the oxygen and the ligand/central atom

Lizette Noriega 1H

Yes, that should be fine because it is true that the stronger an intermolecular force is, the more difficult it is to break the bond

Lizette Noriega 1H

I'd recommend studying with others, attending the UA workshops, and watching YouTube videos that cover the general ideas on the topics we are studying. It is pretty easy to get lost in the class but reserving time to review past material is essential for catching up in addition to making use of thes...

Lizette Noriega 1H

If the orbitals that form sigma bonds overlap more than the pi bonds, how is it that sigma bonds can rotate and have more flexibility than the pi bonds?

Lizette Noriega 1H

Lavelle has a post on Chemistry Community (see link below) where he states that we can turn in the homework for Week 9 and 10 during Week 10

viewtopic.php?f=157&t=52609

Lizette Noriega 1H

The final is cumulative so it will be covering all the topics from weeks 1-10

Lizette Noriega 1H

Will we still have lecture on Wednesday, November 27th or will it be canceled due to Thanksgiving break? Thanks

Lizette Noriega 1H

Lavelle said during Friday's lecture that hybridization will not be included on the test. The cutoff will be at sigma bonds which will be the first slide on Monday's lecture

Lizette Noriega 1H

The test will cover material after the midterm which has been very conceptual thus far. I don't think certain calculations are required but I would suggest checking in with the TAs

Lizette Noriega 1H

What is the relationship between boiling points and the type of intermolecular force? Are boiling points dependent on the strength of the force? Thanks!

Lizette Noriega 1H

Out of the following interactions, is this the correct order from strongest to weakest bond?

ion-dipole > hydrogen bonds > dipole-dipole > Van Der Waals

Also, is Van Der Waals the same as London Dispersing forces? If not, what is their difference? Thanks!

Lizette Noriega 1H

As far as everyone knows, we will have a lecture on Wednesday before Thanksgiving. You can always double-check with the TAs or with Lavelle beforehand though

Lizette Noriega 1H

For next week's homework are we turning in questions from the Chemical Bonds section or do we move onto Molecular Shape and Structure?

Lizette Noriega 1H

(# of valence electrons) - (# of electrons + # of bonds) = formal charge

or if you want an even simpler way of thinking about it: (# of valence electrons) - (# of dots + # of lines)

Lizette Noriega 1H

It's best to always draw resonance structures if the molecule has them. It demonstrates your understanding and it's just safe to have even if you aren't being directly asked to provide them

Lizette Noriega 1H

How do solubility and ionic/covalent character relate to one another? Is ionic character more soluble and covalent character less soluble?

Lizette Noriega 1H

Yes, that's correct. The grades will be dependent on the number of points and the cutoffs made by Dr.Lavelle with regards to the class average

Lizette Noriega 1H

The bond lengths in resonance structures will be an average of all the present bonds; this is due to the creation of a resonance hybrid which creates another molecular structure from all the other existing resonance structures

Lizette Noriega 1H

Watching YouTube videos and taking notes on them has been very resourceful for me. It helps me gain a better understanding of the concepts for equations and the main topics of our classes.

Lizette Noriega 1H

Hello, I just need clarification on threshold energy. I know the threshold energy is the energy needed in order to eject electrons from a metal surface but in terms of the equation, is it represented by the work function? Thanks!

Lizette Noriega 1H

Hello,

This is a dumb question but I need clarification as to when you use certain equations since I always seem to mix them up. For instance, what kinds of problems indicate the use of the de Broglie equation (λ = h/mv) in contrast to the equations for wavelength (c= λv) and energy (E=hv)?

Thanks!

Lizette Noriega 1H

Personally I have found YouTube to be very resourceful because the videos provide extra material in addition to lectures which helps me understand the concepts better and relate them to the practice problems we go over. I would also suggest taking notes while you're watching the video because it's h...

Lizette Noriega 1H

Thank you so much!! That makes more sense. The equation editor is really useful in making sense of the math so thanks for that as well.

Lizette Noriega 1H

Hello, could someone explain how to solve for this question? Thanks! "Potassium permanganate, KMnO4, is an inorganic chemical compound used for cleaning wounds. 5.00 g of KMnO4 is dissolved in a 150.00 mL flask of water. If 20.00 mL of this solution is removed and placed in a new 2nd 250.00 mL ...

Lizette Noriega 1H

There's no specific rule as to when you must use the noble gas configuration over the complete electron configuration. My TA said it is much simpler to use the noble gas configuration but to be careful on exams when you are asked to provide the entire electron configuration of an element

Lizette Noriega 1H

I know there is a trend for valence electrons which is to look at the column number to determine the number of valence electrons found in a certain element. Although, this only applies to the s and p blocks.

Lizette Noriega 1H

In what kinds of scenarios or questions would we need to use the Rydberg equation?

Lizette Noriega 1H

Cations are atoms with a positive charge (+) while anions are atoms with a negative charge (-); this is due to the loss or gain of electrons. They are important because they are essential to the formation of ionic bonds, bonds in which electrons are lost or gained in order to reach a more stable sta...

Lizette Noriega 1H

He did mention that he will have multiple review sessions (spread out through his lectures I believe?) but primarily, he mentioned having a large review session on the Saturday or Sunday before the midterm- his only concern is obtaining a large lecture room so that many people can attend. He also me...

Lizette Noriega 1H

I would definitely recommend signing up for AAP's peer learning sessions as well as joining study groups with other classmates. There are many resources out there in addition to tutors. Peer learning sessions offer many study sessions so they are flexible with your schedules- they also do midterm an...

Lizette Noriega 1H

An electron is at its excited state whenever its energy level is higher than its corresponding ground state. During ground state, its electron configuration is at default whereas, during the excited state, it will jump into a high orbital

Lizette Noriega 1H

RichBollini3C wrote:
Diana Chavez-Carrillo 3J wrote:Are the TA's grading our homework based on completion or correctness?

I believe they are grading based on correctness.

Do you know if all the TAs grade based on correctness or does it vary from TA to TA?

Lizette Noriega 1H

Hello, I'm just looking for clarification on the equations that are currently being used in the material we are studying right now. So far, Lavelle has gone over three main equations: the de Broglie equation, Schrodinger's equation, and Heisenberg's indeterminacy equation. Are there any more essenti...

Lizette Noriega 1H

The letter, s, p, d, and f, refer to subshells which are orbitals that correspond to already existing orbitals. Each of the subshells has its own orbitals as well. For example, the s subshell has 1, the p subshell has 3, and so forth.

Lizette Noriega 1H

Anyone enrolled in the course can attend- you just show up to the session!

Lizette Noriega 1H

Hello- are our five weekly posts due by Friday or Sunday? I know we have to post five comments by the end of the week but I was wondering if there was a definite deadline. Thanks!

Lizette Noriega 1H

I don't believe any comments from the previous week carries onto the next- this is to encourage students to interact weekly. I would suggest making five posts per week just to be safe.

Lizette Noriega 1H

You can go to the board index and scroll down until you find the forums. From there, you open the forum that corresponding to the topic of your choosing. After you've opened it, you can click on "New Topic" in order to make a post. Hope this helps!

Lizette Noriega 1H

Like any experiment, there are always side reactions that can occur such as loss of heat, impurities (product sticks to the side of the beaker), or human error (incorrect measurements of reactants). Taking these things into account, the actual yield is going to be less than the theoretical yield bec...

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