CHEMISTRY COMMUNITY

Vance Liu

Long story short, galvanic cells converts chemical energy to electrical energy, while electrolytic cells convert electrical energy to chemical energy.

Vance Liu

Mr. Rice is, imo, is very underrated. Authentic, tasty Chinese food for a decent price.

Vance Liu

Here's another one:

Contrary to what you might believe, lowering your body temperature to -273 degrees Celsius is not 0K

Vance Liu

what differentiates H from G? Is G a specific type of H that goes towards work?

Vance Liu

Just as a refresher, what would be the occasions where you use ideal gas equation PV = nRT vs. -nRT ln(V2/V1)?

Vance Liu

Set your posts shown to "last 3 months". That'll exclude everything from last quarter, and you can see the posts you've done this quarter.

Vance Liu

Think of "initial rate against [A]" as y = mx, with y being the initial rate, m being k, and x being [A]. This works because each initial rate is a constant value, corresponding to a specific concentration.

Vance Liu

When it comes to the final exam it's probably better to know both just in case.

Vance Liu

I think this is a specific case, as the initial concentration for all reactions in the graph is 1M. Second-order reactions are proportional to the square of the concentration, while first-order reactions are proportional to just the concentration. That means that Second-order reactions are more sens...

Vance Liu

Why is the rate enhancement of catalyzed reactions greater at lower temperatures? Achieve mentioned this in the solution for number 20.

Vance Liu

I understand why catalysts lower the activation energy and increase the rate of the forward reaction. However, why does the reverse rate of the reaction also increase?

Vance Liu

For equations where we determine reaction order from half-life values, is there a better way than just plugging into each individual equations for 0th, 1st and 2nd order reactions?

Vance Liu

What would be the units for A in the Arrhenius Equation? Also, A is not on the constants sheet, so would it be given in problems?

Vance Liu

Can the order only be obtained from experimental data? Is it in any way related to the coefficients of the species in the reaction?

Vance Liu

Reactions occur with specific phases. If the phase changes, you're essentially removing the species from the equation. Therefore, if you change the phase of a product, you remove it from the equation, preventing it from participating in the reverse reaction.

Vance Liu

Can q(rev) be substituted for delta H?

Vance Liu

kinetic stability is determined by the speed of the reaction, while thermodynamic stability is determined by the spontaneity of the reaction. Since the conversion from diamond to graphite is slow but spontaneous, it is kinetically stable but thermodynamically unstable.

Vance Liu

The greater the value of the standard reduction potential, the easier it is for it to undergo reduction, and therefore it is a better oxidizing agent.

Vance Liu

Apparently, Pt is added when there is a lack of a solid conductor. If half-reactions are only aqueous or contain a solid that is non-conductive, then platinum is added to the reaction and the cell diagram.

Vance Liu

I don't know about H+ and OH-, but H20 is present on both sides of the reaction so you can omit it from the reaction and cell diagram.

Vance Liu

From what I understand, the phases are listed in the order in which they are in contact. So the order in the half-reactions is the same order that you would put in the cell diagram.

Vance Liu

The solution for Achieve #7 says: In the shorthand notation, the anode is written on the far left and the cathode on the far right. The different phases in the cell are separated by a vertical line, and the phases are listed in the order in which they are in contact. The salt bridge is represented b...

Vance Liu

The redox reaction of a standard hydrogen electrode serves as a basis (comparison) for all other reactions, since the standard potential is 0.

Vance Liu

What would the potential of a standard hydrogen electrode (S.H.E.) be under the given conditions? [H+]=0.50 partial pressure H2=1.3 atm T=298 K I know this isn't exactly electrochem related, but how can we use the both partial pressure and concentration for the reaction quotient? I thought it was ei...

Vance Liu

I'm not sure, but every pure element seems to have 0 delta H of formation and 0 Gibbs free energy of formation, so I'm assuming the reasoning behind why pure elements have 0 standard enthalpies of formation (the equation for the formation of O2 is defined as O2(g) => O2(g), so delta H of formation i...

Vance Liu

More complex compounds have more atoms, and with more atoms, there are more ways to vibrate. More vibrational motions = greater entropy. Also, with more atoms, there are more extreme positive and negative charges, further affecting the motions of the atoms.

Vance Liu

At 0K, there should theoretically be no entropy. there is entropy, however, and it comes from the positional disorder of the particles, so it is "residual". However, the entropy is minimal as at 0K there is only one microstate for the particles.

Vance Liu

How do we remember which is which? I remember Lavelle mentioning a method to remember but I'm still struggling to identify which is which.

Vance Liu

im pretty sure for a particle with two possible positions, the equation of possible states is W = 2^n, where n is the number of particles. if the number of particles is a mole of particles, or avogadro's number of particles, then you raise the # of possible positions to the power of avogadro's numbe...

Vance Liu

I'm pretty sure absolute entropy is the entropy change from absolute 0K to whatever temperature you're measuring. And for any reaction, where there is change there will also be a change in order, meaning a negative or positive change in order. I don't think it's possible for zero change in order, ot...

Vance Liu

The standard Gibbs free energy should be in the chempendix thermodynamics tables, make sure you use different G values for H2O (liquid) and H2O (gas).

Vance Liu

How does entropy relate to molecular orientation? Does it have to do with the degeneracy? There was a question on the Achieve homework week 5-6 that said: On the basis of the structures of each of the molecules, predict which compounds would be most likely to have a residual entropy in their crystal...

Vance Liu

When do we use either equation when calculating work?

Vance Liu

I get the concept of delta H and delta S for heat transfer and entropy respectively, but what exactly does delta G free energy represent? I only understand how to interpret delta G in terms of spontaneity.

Vance Liu

Everything seems right except the first thing you said. The work is energy of expansion, not compression. The second law simply establishes the idea of entropy as a concept (heat/temperature) , and the third law states that as the temperature approaches absolute 0K (zero energy), the entropy also ap...

Vance Liu

Higher degeneracy = more possible states = more disorder = higher entropy

Vance Liu

I know that entropy changes due to volume and temperature, but can it change due to pressure as well?

Vance Liu

Always think product over reactants (products/reactants). Lets say K is 1, and Q is 2. For Q to go to K, reactants would have to increase and products would have to decrease, favoring the reverse reaction. If Q is 1/2, the opposite is true. Products would have to increase and reactants would have to...

Vance Liu

Cp is also related to Cv through the equation: Cp = Cv + R.

Vance Liu

Q: Why is gold the best element?
A: Because it's AU-some.

Vance Liu

they give you pH, so you can convert that to pOH then [OH-]. You know that NH2NH2 yields NH2NH3+ and OH-, and since its 1:1, [NH2NH3+] = [OH-]. from there you set up an ice box and solve for X which is the initial concentration of NH2NH2 (initially [NH2NH3+] and [OH-] = 0)

Vance Liu

I think of it like this:
endothermic = taking in heat, adding more heat (increasing temperature) leads to more endothermic reaction. in other words, treat heat as a reactant or product when thinking about these problems.

Vance Liu

HA -> H+ + A-

percent protonation is as such:

[A-]/[HA] * 100%

Vance Liu

You don't know the initial concentration of B because the information they give you refers to a system already at equilibrium. You could, in theory, do the work to find the initial concentration of B and you could use that, or you could just add all the B present at equilibrium (formal concentration...

Vance Liu

Maybe try ice chart first to see the concentrations at equilibrium. I think you assumed the molarity was the equilibrium value, so try considering the given molarity as the initial value instead.

Vance Liu

When working with chemical equilibrium of solutions, you always want to convert to mol/L. The K equations only work with molarity or partial pressure.

Vance Liu

Al can act as a weak acid (its strong electronegativity pulls oxygen atoms in water closer to it, weakening O-H bonds and allowing H+ to form) The equation: Al3+ + 3H2O --> Al(OH)3 + H+ from here you do your typical ice box stuff (ignoring H2O and Al(OH)3) since you know the concentration of Al3+ . ...

Vance Liu

If initially, you have .0709 bar of PCl5 and no PCl3 or Cl2, how did you end up with .0752 bar of PCl5? At equilibrium, PCl5 should have a lower pressure than the initial value. My guess is that you used the wrong value of x (since quadratic equations give you two values of x that satisfy the equati...

Vance Liu

As a rule of thumb, the side with the least amount of moles will always be favored when volume decreases.

Vance Liu

If it gives you partial pressures and Kp, then you proceed as you would with concentrations and Kp. You would only need to convert if you were given Kp and concentrations, or Kc and partial pressures.

Vance Liu

Probably not. Like usual, we'll have the list of formulas and constants and a ptable. We'll probably have to memorize the naming method for coordination compounds.

Vance Liu

Maybe since C is bonded to another C, the orbitals are not hybridized as they are with a H to C bond.

Vance Liu

when an octet is fulfilled, it fills up the p sublevel. In order to go beyond an octet, d orbitals need to be utilized (in period 3 and after) in order to accommodate for the extra electrons. Thus d orbitals are also utilized in the hybridization past an octet (dsp3, d2sp3)

Vance Liu

I know this delves more into biology a bit, but I'm curious about the structure of wagyu beef. What makes it different from regular angus or other varieties? I know that the fat melts easier at room temperature, and how the fat influences the Maillard reaction when cooking it in a pan.

Vance Liu

This doesn't really have anything to do with cooking, and I'm unsure if someone already mentioned this... but I was thinking back to when I was younger and watching my mom prepare food around the house. I remember she'd cut apples and let them soak in orange juice, so they don't brown as quickly. B...

Vance Liu

This doesn't really have anything to do with cooking, and I'm unsure if someone already mentioned this... but I was thinking back to when I was younger and watching my mom prepare food around the house. I remember she'd cut apples and let them soak in orange juice, so they don't brown as quickly. B...

Vance Liu

The amphoteric oxides are similar to the metalloid diagonal band, but moved over to the left a bit and includes lead and arsenic.

Vance Liu

Amphoteric compounds can react with either acids or bases, thus they have either acidic or basic character. Metal oxides are common amphoteric compounds (metal ion + oxygen) and can react with bases (cation + OH-) or acids (H+ + anion).

Vance Liu

nitrogen in NH3 is already pretty stable (fulfilled octet), so the electrons are less likely to attract an H+ ion.

Vance Liu

We classify strong bases by their ability to dissociate into cations and OH- ions in water. Since Mg and Be form strong bonds with OH-, it is harder for them to dissociate in water thus making them weaker bases. Same thing with HF, which has very strong bonding, making it a weak acid.

Vance Liu

think about how pi bonds are formed (two regions of e- density above and below the atoms on an single axis). Consecutive pi bonds will have regions of e- density on different axis. for example, x axis pi bonds will be followed by y axis pi bonds, which will be followed by x axis again and so on. thi...

Vance Liu

cis- means polar, trans- means nonpolar.

Vance Liu

ohhhh i completely forgot about the # of protons that was the missing piece. Thank you for your response!

Vance Liu

I understand that across a period, atoms of elements get smaller because more e- in the same energy level decreases the shielding effect and causes atoms to become more tightly compact. However, with ionic anions, even though they gain e- , the ionic radius is greater than the atomic radius of the s...

Vance Liu

P can hold a normal octet (8 e-) plus 2 more e-, 10 e- total. This is because n=3 has an extra 3d subshell available for bonding, so a fully bonded P should be 3(s2p6d2)

Vance Liu

halides in general refer to any cation bonded to elements in group 17, or halogens. also notice that when halogens are bonded to cations the names take the "ide" suffix (NaCl, Sodium Chloride)

Vance Liu

the formulas will probably be provided, but it doesn't hurt to know some of these basic formulas by heart!

Vance Liu

As a rule of thumb, all molecules have London dispersion forces.

Vance Liu

Bismuth most commonly has a charge of 3+. I think that it could lose 5 electrons, but the chances of that occurring are relatively uncommon. You are also correct that as you go down the periodic table for post-transition metals, s orbitals are less likely to be ionized.

Vance Liu

I think that even if these silver halides have "covalent" characteristics they are still considered ionic bonds. At the end of the day, you have an Ag+ cation bonding with a F-, Cl-, Br- or I- anion, which still counts as an ionic bond.

Vance Liu

For some reason, I always find myself stress-baking during finals week--just to get my mind off things. I can relate to this one. I'm stress-making boba and drinking way too much tea. It's scary and yet so tasty. My weighing scale going up up up. Boba has to be my ultimate weakness, I could save a ...

Vance Liu

It's always useful to memorize these equations, even if they're given anyways. Saves valuable time!

Vance Liu

from what I understand, the oxidation number of a compound is equal to the total charge. for example SO4^2-, has an oxidation number of 2-. since O has an oxidation of 2-, and their are 4 O atoms, S has to be +6 in order for the total charge to be 2-.

Vance Liu

check the periodic table. usually far left side and far right form ionic bonds. covalent bonds are formed among the elements on the left side of the periodic table, in the p-orbital group. Also, covalent bonds are usually formed amongst nonmetals, and ionic bonds are between metals and nonmetals.

Vance Liu

https://www.youtube.com/watch?v=QXT4OVM4vXI

this video is helpful to understand chemical bonding imo

Vance Liu

Metallic bonds are generally weakest because of the "sea of electrons" between metallic atoms (which allows metals to be so malleable).

Vance Liu

I think it means just in the way that formal charge and bond lengths are done, it reflects a more covalent view of molecules (where electrons are shared between two atoms instead of being completely transferred from one atom to another)

Vance Liu

You should have been able to use the equation Ephoton - work function = Ek. Rearranging the equation, we get that Ephoton = work function + Ek. From the previous part b, we know that the work function is 1.66 x 10^-17 J so we have Ephoton = 1/2mv^2 + 1.66 x 10^-17 J. Plugging in the velocity that w...

Vance Liu

Question: The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.5x10^16 Hz. How much energy is req...

Vance Liu

I would honestly just go through the motions and calculate the energy using the wavelength (answer in joules/protons) and then convert joules to eV. I also believe that the .137eV they give you represents energy/electrons so in that case, it is simple subtraction. They flat out tell you that "e...

Vance Liu

Also since e- are the closest to the nucleus at the principal level, it would take more energy to get them to/and from the principal level and since energy is directly proportional to the frequency, the frequency would also be higher.

this may not be correct just my interpretation

Vance Liu

For any aspiring cooks out there,

Binging with Babish and Josh Weissman are two of my favorite youtubers. They are very in-depth and go through complex recipes step by step. Binging with Babish is more into the how of cooking while Josh is just funny. Check them out!

Vance Liu

I keep hearing the term "wavelike" getting thrown around, but can anyone actually describe what makes something have "wavelike" properties? What does that mean and how is it different from having "particlelike" properties?

Vance Liu

Can someone explain how Ψ^2 represents the probability of finding an e-?

Vance Liu

I'd like to point out that yellowjacket was hit by a toy brick thing and completely knocked over but then got hit by the toy train in the next 10 seconds and was completely fine, so I don't think the laws of physics/reality work in Ant-Man at all. Fun movie tho

Vance Liu

So pretty much any element besides H would be a "multi-electron system" and thus the Bohr model and En = -hR/n2 wouldn't work.

Vance Liu

Depends on what element we're talking about here. Some elements are ionized by UV while others are not, since different elements have different wavelengths and frequencies on the EM spectrum they react with.

Vance Liu

Without a vacuum, the speed of light is different and since you multiply frequency and wavelength, the wavelength will also be affected. Being in a vacuum allows wavelength/frequency to be quantified and compared on the same level.

Vance Liu

I remember professor Lavelle saying that the equation is based on experimental observations of the hydrogen atom, and wouldn't work for any other element given that only hydrogen has one electron.

Vance Liu

In terms of actual practicality, I find it a lot easier to write down how much of each element you have at first below the equation. That makes it easier to visualize the amounts and solve easier without the risk of making mistakes with mental math.

Vance Liu

I usually keep two decimal places after each mass (H=1.01,c=12.01, etc.). That's just how I did it in HS chem and it keeps it precise enough without being ridiculously precise.

Vance Liu

Wow, these jokes are so hilarious! Here's one.

I tell only bad jokes because the good ones argon.

I'm a comedic genius.

Vance Liu

have yall ever blown up a hardboiled egg in the microwave before? why does that happen?

Vance Liu

Lorena_Morales_1K wrote:This is so fascinating, I am not much of a cook myself but I definitely want to start to cook and make connections to the chemistry we're learning because it sounds super dope.

Cooking is such a good way to really see chemistry in action. plus, its fun!

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