CHEMISTRY COMMUNITY

SophiaNguyen_2L

Hello! Dr. Lavelle wrote this equation down when he was explaining enthalpy and I don't quite understand the circumstances where qp would equal delta H. If someone could explain this, I'd really appreciate it! Thank you.

SophiaNguyen_2L

I believe q denotes heat, which is basically a transfer of energy in chemical reactions. On the other hand, H is enthalpy, which is a state property.

SophiaNguyen_2L

I really like taking a walk when it's warm and sunny outside while listening to music!

SophiaNguyen_2L

Hello! Can someone explain why compressing the system (for part b) has little or no effect? I had thought that compressing a system meant that you're changing the volume, which in turn affects the pressure? Thank you in advance!

SophiaNguyen_2L

Hello! So for this problem, I found x = 4.3*10^-5 and used that to find the concentrations of CO2 and CO, which were [CO2] = 8.6*10^-5 and [CO] = 4.9*10^3. According to the solutions manual, this is correct. However, using the same x value, I found the concentration of O2 as [O2] = 4.6*10^-4, while ...

SophiaNguyen_2L

Yup! Your reasoning seems sounds to me :))

SophiaNguyen_2L

Hi! So dividing a number by 0.5 is actually the same as multiplying the number by 2. So the solutions manual still ends up with a mol/L concentration. Hope this helps!

SophiaNguyen_2L

I think most times, you're going to have to use an ice table unless the problem explicitly states the concentrations all the reactants and products at equilibrium. From what I've noticed in the Sapling homework, problems that typically just say that a reactant/product is placed in a container to rea...

SophiaNguyen_2L

Hello! So for most of the problems I've encountered, either the reactants or products start off with 0 in the beginning of the reaction. However, I'm sort of confused on how to determine which side would have positive/negative x if both the reactants and products have initial values greater than 0. ...

SophiaNguyen_2L

I think reading this part (chapter 5H) of the textbook is super helpful! It goes over ways to manipulate chemical reactions and their K value. I'll use part c as an example. Since the problem gives you N2(g)+3 H2(g)⇌2 NH3(g) with a K value of K=41, you can multiply the entire equation by 2 to get th...

SophiaNguyen_2L

Hello! Can someone please explain to me why there are different values for some of the reactions listed in Table 5G.2? I had thought that K was the umbrella term and Kc/Kp fell under it. However, that relationship of K and Kc doesn't make sense if there are two different values in the table. If some...

SophiaNguyen_2L

Hello! For part c of this problem, the answer is that the ratio of O2/O3 in the two containers is different. Can someone explain why that is? Thank you!

SophiaNguyen_2L

Hello! Just to verify, when a problem says an electron goes from a certain energy level to ground state, that just means that it goes to energy level n=1 right? Thank you in advance!

SophiaNguyen_2L

I started by assigning the variable x to [H + ]. For our new pH (pH 2 ), we would have 0.12x M as our concentration. The rest of my process went like this: 1) I wrote out the equation for pH. pH 2 = -log(0.12x) = (-log(0.12)) + (-log(x)) 2) -log(x) is the same thing as the original pH, so we can re...

SophiaNguyen_2L

Hello! This question asks to identify the following as a Lewis acid or base. a)NH3 b)BF3 c)Ag+ d)F- e)H- The solutions for this proble won't load for me (no matter how much I refresh :') ), so I was hoping that someone could go over my solutions and tell me which ones I got right or wrong. I got: a)...

SophiaNguyen_2L

Hello! Toolbox 9C.1 in the textbook says this complex is called hexacyanidoferrate(II). However, the textbook also had this complex in a problem and its answer key says it's called hexacyanoferrate(II). The difference is just the "-ido" after the cyano. Which name is correct? And could som...

SophiaNguyen_2L

Hello! For this problem, the compound is: CH20, with C being the central atoms and the other three atoms surrounding it. I had thought that only the C atom had a hybridization of sp2. However, the textbook says that both the C and O are sp2 hybridized. Can someone please explain why that is for me? ...

SophiaNguyen_2L

Hello! Can someone please explain what it means when the s-character increases/decreases in a molecule? What exactly is the s-character and how does it affect bond angles? Thank you!

SophiaNguyen_2L

Hello! I'm going over some textbook problems and encountered a molecule with a linear shape. The textbook said it had a bond angle of 180.5 degrees and I was hoping someone could explain to me the cases where the bond angles are slightly different from what is expected. Thank you in advance!

SophiaNguyen_2L

Hello! For this problem, the compound is N20. How would you determine which atom is the central atom? Thank you!

SophiaNguyen_2L

Hi there! So I believe a ligand is any ion or molecule that binds to a central atom (usually a transition metal) to form a coordination complex and the molecule/ion can only form a coordination complex by donating one or more of its electron pairs. Ligands are important because they form coordinatio...

SophiaNguyen_2L

Hello! For part b) of this problem, it asks to determine whether or not a molecule with a bond angle of 180 degrees must have, may have, or may not have a lone pair(s) of electrons. I thought it didn't require a lone pair. However, the back of the textbook said it may have lone pairs. In what instan...

SophiaNguyen_2L

Hello! Can someone please explain what exactly is an oxidation state? What does it mean? Thank you!

SophiaNguyen_2L

I feel like I'm understanding the content so far, but I still don't feel very confident for the final :/

But no matter what, I'm going to study my hardest and hope for the best. Best of luck to everyone!

SophiaNguyen_2L

Hi! I feel like these images can help visualize the sigma/pi bonds. Hope this helps!

SophiaNguyen_2L

Hello! Can someone please explain to me what it means for pi bonds to be parallel or perpendicular to each other? And how do you determine when they're parallel/perpendicular? Thank you!

SophiaNguyen_2L

Hello! The last part of this problem asked if AsO4 -3 was polar or nonpolar. I initially thought it was polar, however the solution said: "Although the bonds here are polar, the molecule is not due to resonance and the symmetrical shape of the molecule." Could someone please clarify this f...

SophiaNguyen_2L

Hi! So for this problem, all you'd have to do for the sigma bonds is count how many bonds there are in total (both single and double bonds). So that would be 13 sigma bonds. Then you'd count just how many double bonds there are, so there would be 3 pi bonds.

SophiaNguyen_2L

Hi! In the photo you attached, that's actually just methane, which has one carbon. Trans-dichloroethene actually has two carbons, which is why the chlorines do in fact are placed opposite from each other and cancel each other's dipole moments. Hope this helps!

SophiaNguyen_2L

Hello! I'm having trouble with this particular problem. What exactly are axial and equatorial atoms? Thank you!

SophiaNguyen_2L

Hello! Can N have an expanded octet? If yes/no, why/why not?

SophiaNguyen_2L

Hello! I read a portion of the textbook for some help with this problem. So s-electrons are found very close to the nucleus, which is why they're more likely to "penetrate" the nucleus, which basically just means that they may be found within the inner shells of an atoms. Since they're so ...

SophiaNguyen_2L

Hello! So in today's lecture, there was a statement that said: repulsion strength: lone-lone pair > lone-bonding pair > bonding-bonding pair What exactly does this mean? I think I'm confused because I don't quite understand the concept of a lone-bonding pair or a bonding-bonding pair. Is it the same...

SophiaNguyen_2L

I think the difference in the naming between the two is the number of O atoms in the molecule. It's the same idea with phosphate (PO4 -3) and phosphite (PO3 3-). I honestly haven't heard Professor Lavelle mention nitrite very often, nor do I recall encountering problems that mentioned nitrite, so I ...

SophiaNguyen_2L

Hello! So to my understanding, the bond angles in PCL5 are in fact maximized. It's just that there are more atoms attached to the central atom in PCL5 than in CH4, so there are more atoms & electron repulsion in the same space. The 90 degrees bond angle is the how the linear atoms compare to the...

SophiaNguyen_2L

All you'd have to do is set the charge of the atoms equal to the overall charge of the compound. So it'd be like:

4(O) + (Cl) = -1
4(-2) + (Cl) = -1
-8 + (Cl) = -1
Cl = +7

SophiaNguyen_2L

Hello there! So for finding the most plausible structure based on formal charge, you'd have to look at charges they give you in each photo. The most stable structure would be the one(s) that result in the lowest value of formal charges throughout the molecule. So in this case, it'd be structure C b/...

SophiaNguyen_2L

Hi! I do something really similar to the comment above me. I simply count the electrons that are actually touching/surrounding the atoms. With lone pairs, those are easy since you can just count the "dots" we use to represent the electrons. With bonds, I just count the end(s) of the bond(s...

SophiaNguyen_2L

Hello! So basically, do H-bonds only happen when there's another compound with an atom that has a lone pair of electrons? In general, what compounds have H-bonds, because so far, I only hear H20 as a compound with H-bonds. Thank you!

SophiaNguyen_2L

I think it's because electronegativity is the tendency of an atom to attract a shared pair of electrons. Therefore, in a compound, it would make sense to an atom with high electronegativity to attract the electrons in a compound, thus making it more negative than the rest of the atoms in the compound.

SophiaNguyen_2L

Hi! I think in the case of hydrogen, helium, lithium, and boron, they simply have too few valence electrons to begin with in order to be stable at a state in which they have 8 valence electrons. Hope this helps!

SophiaNguyen_2L

It looks like the people above me already explained the octet rule, so I'll just mention some common elements that don't follow the octet rule. These include: - boron & aluminum, who often can form compounds in which they only have six valence electrons -hydrogen, helium, & lithium because t...

SophiaNguyen_2L

For lewis structures, lone pairs represent an atom's pair of electrons that don't contribute to a bond of any sort with another atom. So in other words, the lone pairs are electrons that are nonbonded.

SophiaNguyen_2L

Hello! So I'm watching today's lecture and I'm curious as to what the greek letter for the slightly negative/positive atoms in the covalent bond is? What's it called and how to you write it haha. And just to be sure, that particular letter just means that an atom is positive/negative right? Thank yo...

SophiaNguyen_2L

Hi! I think it's because since the electrons can move around, they can fill up the orbitals of other atoms to complete a full octet. This would make the molecules less likely to react I believe, so that's why it'd be more stable

SophiaNguyen_2L

I think ionic bonds are stronger because there's a stronger attraction between the oppositely charged atoms. And I think since covalent bonds are just atoms sharing electron pairs, it'd take less energy to break apart covalent bonds.

SophiaNguyen_2L

Hello! I might be wrong, but I don't think it really matters which way the electron spins first. I think Professor Lavelle and other educators tend to write that the electron spins clockwise first because the arrow signifying that tends to be written on the left first, if that makes sense. So to ans...

SophiaNguyen_2L

Hello! Is there a way or a trick to remember what elements on the right side of the periodic table are non-metals or metalloids? I tend to get confused which ones are which. Thank you in advance!

SophiaNguyen_2L

Hello! So in the lecture, Professor Lavelle talked about one electron moving out of the 4s shell and filling up the remaining spot in the d-shell. I'm just curious as to why the same thing doesn't happen when there are 3 or 8 electrons in the d-shell. Is it not possible for both electrons in the 4s ...

SophiaNguyen_2L

Hello! So I've encountered some problems that ask me to find kinetic energy and it either gives me wavelength or frequency. I've messed up on problems because I used the E=hv equation instead of the DeBroglie equation and I wanted to know if there was a way to know when it's the right time to use ei...

SophiaNguyen_2L

Hello! So the question is: Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the electrical field at a given point ...

SophiaNguyen_2L

I think it's good for us to memorize how to convert from m to km and g to kg. I like to think of kilo as 10^3, which means I'd just have to move the decimal place 3 times. When going from m to km, you move it 3 places to the left. From km to m, you move it 3 places to the right. Same idea for grams ...

SophiaNguyen_2L

While we're on this topic, can someone explain what an Angstrom is and how to convert to it from meters? An Angstrom simply just another unit of measurement and is 1.0 * 10^-10 meters. To convert from meters to Angstroms, you'd have to move the decimal ten places to the right. To convert from Angst...

SophiaNguyen_2L

During my discussion section, my TA applied sig figs once we were finished with our calculations. I think the answer is more precise that way.

SophiaNguyen_2L

Hey there! If I remember correctly, you don't have to worry too much about this equation for this course. But to answer your question, I think the Schrodinger Equation is a mathematical expression that describes the energy and position of an electron.

SophiaNguyen_2L

Hello! I'm a little confused about some of the equations Professor Lavelle wrote on his whiteboard during the lecture at minute 38:35. From what I understand, p(momentum)=m(mass)*v(velocity). Below that equation he had on the board, Professor Lavelle wrote "E=pc." I'm confused about this b...

SophiaNguyen_2L

Hello! Sorry if this is a dumb question, but in the lecture on 10/14 about Atomic Spectra & Energy Levels, Professor Lavelle emphasizes that an electron needs a photon that matches the energy difference between ground states in order for the electron to move from one to the other. My question is...

SophiaNguyen_2L

Was that Jack Johnson? For the song of the lecture on 10/14 ?? What song was it haha

SophiaNguyen_2L

Hey there! I think using h would be sufficient in your work, since it's a lot neater and less of a hassle if you use it. Just don't forget to plug in the number in your final calculation and you should be all set!

SophiaNguyen_2L

I believe a higher frequency means that a photon itself has more energy. So yeah, more energy per photon. Hope this helps!

SophiaNguyen_2L

Since it gives you the mass in N2, you can use that value to find the mols of N2 and then just use stoichiometry to convert the mols of N2 to N. I think it'd be easier to use the mols of N to find the empirical formula of caffeine.

SophiaNguyen_2L

Yeprem wrote:Does anyone know if we have to remember what the planck's constant is or is it going to be provided to us?

I am 90% positive that the constant is given to us on a formula sheet or something of the like, but I think it'd be best to either ask a TA or Lavelle himself to make sure.

SophiaNguyen_2L

Hello! Can someone explain to me what exactly is a photon? I can't seem to wrap my head around the concept. Thanks!

SophiaNguyen_2L

For me, I round anything within 0.1 of a whole number to the whole number, and so far it's worked. Aside from that, values like 1.5 or 1.25 or even 1.2, I personally tend to multiply to get it to a whole number.

SophiaNguyen_2L

Yup! You do have to calculate the molar mass for each because you want to convert the given masses into mols for the molecules and then use stoichiometry to find the mols of C and H used in the reaction. So basically, you're finding the mols of C and H the reaction uses from the given masses of CO2 ...

SophiaNguyen_2L

Hello! I was hoping someone could explain to me how to use density in stoichiometry problems. I encountered a problem and it only gave me the reactants' densities, their volumes used in the reaction, and the mass of the product.

Edit: Haha yeah, the problem is Homework 1, #10 on Sapling.

SophiaNguyen_2L

I feel like unless it's specifically asked of you to give an answer with a particular unit, you should be okay with giving an answer with a "common" unit. I remember there was one question in the "Fundemental E" section where the unit in the question was in picometer, but the ans...

SophiaNguyen_2L

I believe the moles of the solute will stay the same because typically when you're diluting a solution, you're simply just adding water to change the volume of the solution. Doing so decreases the molarity of a solution.

SophiaNguyen_2L

https://docs.google.com/document/d/1t0E ... 6rsf0/edit

The above is a google doc he sent with directions on how to get Sapling

SophiaNguyen_2L

Professor Lavelle just sent us an email regarding that!

SophiaNguyen_2L

Hey there! So far with the textbook work, I've encountered problems that did give us a balanced equation. However, as I got towards the end of the assignments, I noticed that the equations weren't balanced. So my guess is that as we move on to more advanced chemistry, we won't be given balanced equa...

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