CHEMISTRY COMMUNITY

Michelle N - 2C

Hi Dr. Lavelle,

Thank you for these last two quarters. I won't lie, I was stressed. Chemistry was never my strongest subject, and I knew that I would need to push in order to be okay. Thank you for your resources, and thank you for your hard work. Stay safe Dr. Lavelle! :)

Michelle N - 2C

Can someone explain to me about the relationship about the higher the rate constant, the shorter its half-life? Thank you!

Michelle N - 2C

Chemical Equilibrium for me! :)

Michelle N - 2C

Adding on, how common are these again?

Michelle N - 2C

Is this just a pattern I noticed, or are natural logs usually first-order rate laws? Can someone explain to me why they are/aren't?

Michelle N - 2C

Thank you for everything you've done Lyndon! We truly appreciate it!

Michelle N - 2C

I am feeling the exact same way. I am highly concerned about both my grades and my safety. The TAs' and UAs' sessions are extremely helpful, but I am conflicted on going to them because of what's going on. I am trusting that they (meaning the department, Dr. Lavelle, etc) are working on a solution t...

Michelle N - 2C

Just to add onto the question, when do we add Pt(s) to both sides of the cell diagram?

Michelle N - 2C

005384106 wrote:At what point do you add elections to the half reaction?

I believe it's when you need to balance out the charges.

Michelle N - 2C

What's the purpose of the nernst equation, and what are all the things the nernst equation can be used to find for?

Michelle N - 2C

When would we have to mention a metal into a cell diagram?

Michelle N - 2C

During week 7, there was in an example regarding calculating the potential difference on Cu/Zn battery (Cu2+(aq) + Zn(s) ---> Cu(s) + Zn2+. It was then stated that the E°Cu was 0.34 V and that E°Zn was -0.76 V. So, I wanted to ask: 1) If given a problem similar to this, would the E° values be given?...

Michelle N - 2C

When do we use the Nernst equation compared to the other equations for electrochemistry? In all honesty, I've been basing off what's given in the problem and what it asks. I know this is not the best way, but for me, this is how I've been going with it. However, I do know that the simplified Nernst...

Michelle N - 2C

I think for this case - balancing redox reactions - I think it's either or since the primary goal is the balance them and their respective elements/charges.

Michelle N - 2C

I just wanted to add to this question, are they also separated when it's a different phase? Can someone explain that aspect to me? Thank you.

Michelle N - 2C

Like what everyone was saying, you add H+/OH- to balance the number of hydrogen atoms present and the same for oxygen. You know how much to add by basing of the coefficients, similar to balancing chemical reactions back in Chem 14A. Hope that helps! :)

Michelle N - 2C

You would balance the charges out by adding e- where needed to make the charges equal. That is where you should be able to find the moles of electron. Sorry this isn't as detailed, but that's what I know.

Michelle N - 2C

As I'm reviewing and rewriting my notes, I wrote down that Dr. Lavelle provided an example about a bike when talking about the 3 ways of changing the energy of system. Can someone explain to me what this was again, and why it was related to this particular topic? Thank you! :)

Michelle N - 2C

F stands for Faraday, which represents the charge of one mole of e-. It should usually be given unless indicated.

Michelle N - 2C

E° is intensive basically means that it doesn't rely on how many times the reaction occurs. The voltage difference will always remain the same, which is why in the example that Dr. Lavelle did on that day, he did not multiply E° by the coefficient to balance the equation.

Michelle N - 2C

Can someone provide a general explanation of this graph? This was shown on Wednesday at the beginning of the lecture, and then a variation of this diagram was drawn today, and I'm just trying to understand the concept of this. Thank you in advance!

Michelle N - 2C

805097738 wrote:What is the nerst equation?

It's the equation E = E° - (RT/nF) lnQ ^^ the one mentioned today!

Michelle N - 2C

Ryan Chang 1C wrote:In cell diagrams, is it possible for platinum to only be on one side?

I would like to add to this question. Is graphite also considered an inert conductor? Why/why not?

Michelle N - 2C

Hiii! Thank you! ^^ :) I did not take a picture of the table when I was borrowing it.. that makes a lot more sense now.

Michelle N - 2C

A constant volume calorimeter was calibrated by carrying out a reaction known to release 3.50kJ heat in a .200 L of solution in the calorimeter resulting in a temperature rise of 7.32 degrees C. In another experiment 100.0 mL of 0.200 M HBr and 100.0 mL of 0.200 M KOH mixed in the calorimeter and t...

Michelle N - 2C

Heat capacity is the amount of heat energy required to raise the temperature of a substance by 1 degrees C. It is extensive because it depends on how much mass there is. The units are in J/C. Specific heat capacity is the heat capacity divided by a certain amount of mass. It is intensive because th...

Michelle N - 2C

(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...

Michelle N - 2C

For a reversible system, the system is isothermal and thus temperature is constant which impacts the formulas utilized since some are used for temperature change and some are used when temperature is constant which is the case of a isothermal, reversible system. Can you or someone here explain what...

Michelle N - 2C

The density can be used toward PV=nRT when there are problems that doesn't give you the moles of the molecule. For example, a problem might give you the amount in mL, and so we'd convert it to moles via density (at least that's what I've been told through the sessions). Hope that helps!

Michelle N - 2C

First, thank you for explaining the ATP part of the biological examples. :) Can someone explain the same for osmotic pressures? I'm not sure we went over this either, but osmotic pressure is basically the pressure needed so that water doesn't pass through a membrane. It's calculated using the conce...

Michelle N - 2C

I think it really depends on what the problem asks/provides. Like what other people said, the common units are J, K, g, L, etc., since they match with the other units when calculating. As long as you know how to convert them, then I think all should be good. Hope that helps!

Michelle N - 2C

What does it mean to have a constant volume or constant pressure? Constant volume means that the volume of the subject would not change, and constant pressure is that the pressure of the subject would not change throughout. These given phrases helps you figure out which equation to use, and which c...

Michelle N - 2C

Hi! I understand through the lecture that an adiabatic system means no heat flow, but I'm a little confused on how this relates to the notes right before it, which was the reversible pathway and the irreversible pathway. Can someone explain this please? Thank you very much!

Michelle N - 2C

I am pretty sure that they are given on the equations sheet. However I think it might be more beneficial to us if we understand the relationships between the equations so that we can work through the problems.

Michelle N - 2C

First, thank you for explaining the ATP part of the biological examples. :) Can someone explain the same for osmotic pressures?

Michelle N - 2C

When I was taking the LS7 series I did PLFs for 7B and part of 7C and found them to be very helpful because they focused on key points as well as extensive practice problems. From what I heard from others, the Chem 14 PLFs are also very helpful, as they help recap the lecture material and go into pr...

Michelle N - 2C

Kind of like what the previous person said, R is a gas constant, so that can't really be changed (given on our equations sheet). For everything else though, yes there could be change. That's also where the mini-questions during lectures are formed "What would happen to ____ if ____ increased?&q...

Michelle N - 2C

Hello! I saw that during the lecture (this was from like week 2), Dr. Lavelle mentioned that the weaker the base, the higher its Kb value is, which is seen when he compared two different Kb values. Although I feel like I understand that, I'd like to know if there were any key conceptual points that ...

Michelle N - 2C

504999222 wrote:If the pressure goes up, would that mean the volume would go down?

Believe it depends on which container and context, but from what I’ve seen in the lecture, yes. It’s like, if you double the pressure, then you halved the volume. Hope this helps. :)

Michelle N - 2C

If I make the assumption because K is less than 10^-3, but the x value is less than 5% do I have to go back and use the quadratic formula to calculate x? I believe the 5% rule applies to when we are to ignore the -x in the problem or not, because what I remembered was that as long as the answer is ...

Michelle N - 2C

Wait ... we got our tests back? I had my discussion on Tuesday and didn't get it back?

Michelle N - 2C

So I’m starting to understand a little bit better about endothermic and exothermic reactions, but I wanted a little clarification here? As temperature increases, so does the equilibrium constant? Sorry, just wanted to have a clear understanding if anything.

Michelle N - 2C

Really depends on what's given, but it's generally through an ICE table with the quadratic formula.

Michelle N - 2C

How do you know which variation of the R constant to use? I know that Test 1 is already over, but in the equations sheet that Dr. Lavelle provided, there were many variations of it. To answer your question, the best way to know which R constant to use is to see the units used in the problem. If it ...

Michelle N - 2C

This is how I've been applying it, but correct me if I'm wrong: Solids and liquids are not included in equilibrium constants. Aqueous elements (aq) are included to find Kc, and gases (g) are included to find Kp.

Michelle N - 2C

They're in Young Hall 3034 (the information office place). What I've seen is that you give the person there your Bruincard and tell them which lecture you're in (Lecture 1, Lecture 3, and Lecture 4). However as of Friday my friend went and they said they couldn't find hers so it's probably a TA or s...

Michelle N - 2C

On our lecture on January 13th, Lavelle stated on his notes that “If we know the concentration of the strong base/acid, we can calculate pH or pOH.” He then proceeded to the example that 0.0030 M of Ba(OH)2 gives 0.0060 M of OH-. How did that happen? Can someone explain to me this specific process? ...

Michelle N - 2C

Hi! So I'm going through some practice problems right now, and I have a general question. It was said through the Step-Ups and I believe once by Lavelle that when solving via the quadratic formula in the ICE table, if the K value is less than 10^-3, then we can ignore the x. Would it matter on the t...

Michelle N - 2C

In class, Professor Lavelle mentioned Le Chatelier's Principle. What is Le Chatelier's Principle and how does it apply to chemical equilibrium and the ideal gas law? Sorry, I don't have a strong background in chemistry because I didn't take AP Chem and don't remember sophomore year's chemistry. Sam...

Michelle N - 2C

You can write it as V is being divided by the whole thing (P = nRT/v). I think why Dr. Lavelle has been writing the V specifically under the n was just emphasize that n/v is molarity, and therefore the concentration.

Michelle N - 2C

It could be equal, but in most cases, it's just constant. Hopefully this graph helps!

Michelle N - 2C

Like what others said, so far we've used this formula to convert between pressure and concentration. I think we'll also be using it to understand conceptual parts, like what happens to the concentration if the pressure increases/decreases/etc. But as of right now, we've only used it for conversion.

Michelle N - 2C

From what I know, K basically tells us that there's a certain ratio needed from the concentrations of products and from the concentrations of reactants so that it could reach equilibrium. With a certain amount available within the solution, there has will be both forward and reverse rates occurring ...

Michelle N - 2C

To add on from the previous reply, an ICE table basically lays out the initial concentration, the change it endures, followed by the equilibrium concentration amount afterward. You start off by writing out the table and then inputting what's given in the problem into its respective spots. From then,...

Michelle N - 2C

You make the two equations into composite equations. Use the two equations that has 2HCl as a product and Br2 + Cl2 as a product. Everything should cancel out and create the equation you are looking for. Make sure that when you add two chemical reactions together you multiply their k values. When I...

Michelle N - 2C

From what I know (and from what everyone said), yep, only used for gases. Partial pressure will refer to one gas in the reaction whereas pressure is all the gases in the reaction. When measuring, the units are usually atm, but since this is on equilibrium constants, we don't put the units. Hope this...

Michelle N - 2C

Hello! So the textbook question states: " A sample of ozone, O3, amounting to 0.10 mol, is placed in a sealed container of volume 1.0 L and the reaction 2 O3(g) S 3 O2(g) is allowed to reach equilibrium. Then 0.50 mol O3 is placed in a second container of volume 1.0 L at the same temperature an...

Michelle N - 2C

For question 5G11, why are some answers written with P and why are some answers written with brackets? Hi! I just wanted to add another question to this same problem because I'm confused when looking at the answers. How do we know if they're asking for partial pressure or concentration? Is there a ...

Michelle N - 2C

Dynamic equilibrium basically emphasizes the idea that when the reactants and products are in equilibrium, that doesn't mean that everything just stays still. Reactions are still occurring, just at the same rate as they're being formed/consumed.

Michelle N - 2C

I remembered something like this: Technically, we should be calculating based on the activity of the reactant/product. However, throughout what we learn here, we assume that the activity is the same as the reactant/product. There was definitely more that he went in depth with, but I wasn't able to c...

Michelle N - 2C

I believe that having a very large K (like larger than 10^3) indicates that the equilibrium strongly favors the products, and that there's a higher amount of products present at some time.

Michelle N - 2C

In general, the significance of K is the same, since it states the equilibrium constant. Kc and Kp just basically denote what the units are. The C would stand for concentration (molarity) and the P would stand for partial pressure. Hope this helps!

Michelle N - 2C

I was confused about this at first, but yes, lone pairs do count in hybridization.

I believe that it's electron geometry when lone pairs do not count. Please double check though!

Best of luck!

Michelle N - 2C

I was in a Step-Up session yesterday, and one of the practice questions was: Place the following molecules of increasing bacidity of the conjugate bases: HOBr, HOCl, HOI. From what I understand, the stronger the acid, the weaker the base. The strength of the acid is then determined by the the bond l...

Michelle N - 2C

When I look at the formula, I look at the reactant and it's equivalent product. If the product looks like it lost a H+, then I know that the product is a conjugate base, and the reactant for it was an acid. The same thing goes the other way: If the product looks like it gained a H+, then I know that...

Michelle N - 2C

nickianel_4b wrote:^^I know that it becomes CH3COO- just from practice, but can someone remind me again why it donates the H+ at the end and not one of the H+ ions attached to the C?

I think that's because they usually lose H+ at the more electronegative atom first, and oxygen is more electronegative than carbon.

Michelle N - 2C

Here's how I work through a problem when identifying acids, bases, conjugate acids, and conjugate bases. Hope this helps you as well, and let me know if there's another method that's more helpful to know: - I know that an acid in general is either a H+ donor or an e- pair acceptor, and that a base i...

Michelle N - 2C

I'm a little confused about what Dr. Lavelle was talking about today (Monday, December 2nd) about how despite what we know about H - F H -- Cl H --- Br H ---- I H-F is the weakest of something? My apologies if this is very out of context, but can someone help me out on this? I'd very much appreciate...

Michelle N - 2C

The question asks: "Which of the following isomers of diaminobenzene can form chelaxing complexes? Explain your reasoning." There were also 3 different figures of the isomers.

First, what are chelaxing complexes? Second, how do you approach and solve this question?

Thank you!

Michelle N - 2C

WUng_1D wrote:Why does cyanide turn into cyano instead of cyanido?

According to Lavelle, they're both the same, but cyano is the older version of the term.

^^ Someone on another chem community post found the link (viewtopic.php?t=2351), so props to them. :)

Michelle N - 2C

Cis generally means when the molecules are next to each other one side, while trans generally means that they're opposite of each other, like across from each other. This applies to cisplatin as that is a well-known chemotherapy drug that stops cell division. In other words, I think the reason why c...

Michelle N - 2C

My TA gave this formula, which I found to be very useful:

(# of metal atoms)(oxidation number) + Σ (# ligands)(charge of ligands) = charge of complex.

To find oxidation number, you make it a variable (x) and then solve for it. Hopefully that helps!

Michelle N - 2C

All the comments above are basically what I wanted to say, but this is where the charges are coming from when working towards finding the oxidation number: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/NamingCoordinationCompounds.pdf Also, I used this equation to calculate the ox...

Michelle N - 2C

A dipole-dipole interaction is when two molecules with partial charges are in contact there. Dipole-induced dipole is when there is a dipole (a molecule with a partial charge) next to an induced dipole (an atom/molecule) without a charge). If it gets close enough, the partial charge on the diple wou...

Michelle N - 2C

what do we need to know about pi and sigma bonds? You need to know how they are presented in bonds. So if there's a single bond, then there's only a sigma. If it's a double bond, it's sigma and pi, etc. It should also be on your notes, where Lavelle showed one bond, double, and so forth. Best of lu...

Michelle N - 2C

Really depends on whether or not the lone pairs are present in the structure. Follow the VSEPR formula (AXE) and you can go from there!

Best of luck!

Michelle N - 2C

Definitely know intermolecular forces (dipole moments) and the concept and shapes from the VSEPR model. Good luck! :)

Michelle N - 2C

Test two covers everything from after the midterm, so like intermolecular forces and VSEPR!

Michelle N - 2C

As of right now, I think it would be given to us, but I would assume that in the future, we'd have to learn it ourselves...

Kinda like how it was H2O (g) for combustion (burning).

Michelle N - 2C

Yes! Some ionic bonds show covalent characteristics while some covalent bonds show ionic characteristics.

Michelle N - 2C

From what I know: Water molecules are a bent shape that allowed the polarity (partial charges) to dissolve well with substances.

Michelle N - 2C

Ionic bonds (although some share covalent bond features) are generally stronger since they are completely transferring electron(s) to the other. Conceptual reasoning is the fact that their electronegativity differences are more drastic.

Michelle N - 2C

From what I know, depending on the non-single bonds and its charges, that's how resonance occurs.

Michelle N - 2C

I noticed that there are two equations:

FC = V + (L+B) and FC = V + (L + B/2).

Both depend on how you count the shared bond?

Michelle N - 2C

Combustion always mean that one of the reactants is O2 and the products are CO2 + H2O. Sometimes, they will add in, like in this problem, an extra product.

Michelle N - 2C

Question

Would the same apply when it's asking for photons?

Michelle N - 2C

I could be wrong in this, but the reason why you can't get the mol of oxygen from CO2 and H2O is because you won't know how much of which is in there. Sure, you can find C then get subtract the rest to get O, but I feel like there's a reason on the fact that both CO2 and H2O contain it. It would be ...

Michelle N - 2C

I know it's already past the midterm, but I think this is for future review, etc.! I saw that it added up to be 99.95%, which might have been a mistake? You can definitely ask Lyndon about it since he made the review sheet! In terms of solving it, a UA actually did a shortcut on figuring out how man...

Michelle N - 2C

The exceptions are due to the fact that 3d^5 and 3^10 would then make the electron configurations back in order in terms of their principle quantum number. I could be wrong, but I think this would apply to all of the elements that are in that column.

Michelle N - 2C

Oh.. yep. Definitely wrote something completely different.

Is oxygen the only exception from this trend then? Asking for future reference and learning.

Michelle N - 2C

Hi, I could be wrong here, but I tend to think back to Schrodinger's Equation, where Ψ^2 represents the probability of finding an electron within those areas. In terms of each orbital, the orbital's shape plays a role in where the electron could potentially be found. With s-orbitals having no nodal ...

Michelle N - 2C

Electrons further away from the nucleus are easier to remove because:

1) Since they're further out from the nucleus (where all the protons are), the attraction is less between the two.
2) The inner electrons often shield them away, but also repulsing them.

Michelle N - 2C

Most elements tend to be in their lowest energy state possible. From what I know... - Forming an ionic bond would allow the oppositely charged (usually) ions to transfer their electrons to result in lowest energy state. - Forming a molecule is similar since they try to achieve a lower energy state. ...

Michelle N - 2C

I am still a little confused about what the Octet Rule is. Can someone explain to me what the concept is?

Michelle N - 2C

Like what everyone said, radicals are basically when the elements are highly reactive since they have unpaired electron(s). This can be noted when there's only one lone pair (the dot) seen instead of two. Most natural elements tend to be in the lowest energy state possible. Therefore, radicals don't...

Michelle N - 2C

An ionic bond is when electrons are transferred to one atom from the other. They usually consist of two atoms with oppositely charged ions (Na+, Cl-). A covalent bond is when the electrons are shared between the atoms, not completely transferred over. That being said, an ionic bond is usually strong...

Michelle N - 2C

They're both generally the same, with the ionic radius being one of the types of atomic radius.

Atomic radius is defined as half the distance between the center of neighboring atoms.
Ionic radius is the then distance of the two ions that are joined by an ionic bond.

Michelle N - 2C

When the d-orbital is not full, they are generally lower in energy. Plus, it would then follow the trend and order of the numbers.

Sorry this is vague, but that's how I was able to get it..

Michelle N - 2C

I went to a Step-Up program a few hours ago, and I saw that the Px, Py, and Pz were just the three coordinates that were for the p-orbital.

Something like this:
____ ____ ____
Px Py Pz

It's basically the three planes as well (3d graph).

Michelle N - 2C

If I understand correctly, it's basically all about how the electrons are pulled/attracted to the nucleus. The further they're out (the larger the atomic radius), the less attraction they'd feel since it's 1) they're further away, and 2) the other electrons are repulsing them as well.

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