CHEMISTRY COMMUNITY

Neel Bonthala 2G

Hey! You can also think about products vs reactants in a concentration cell in terms of diffusion. Molecules in higher concentration regions move to regions of lower concentration. Thus, the reactants move from a region of high concentration to a region of low concentration as products.

Neel Bonthala 2G

Hey! well, you can't really use that equation for a concentration cell because you don't know K. You can't use the given concentrations for K, because it's not at equilibrium. The explanation given above is the reason why E nought is 0 for a concentration cell!

Neel Bonthala 2G

Yeah, why exactly does the final enthalpy change for a mole of TNT become positive? Shouldn't the combustion of TNT also release energy, so it should be a negative value?

Neel Bonthala 2G

In the solution for textbook question 6.57, the manual says to use the half reaction for the reduction of F2 as the reaction happening at the anode. What in the problem tells us which equation to use in the redox reaction? How exactly are we supposed to know to use the F2 half reaction?

Neel Bonthala 2G

According to the solutions manual, we can add up the E nought values from the individual half reactions to get the E nought value of the redox reaction. I remember E values are technically not state functions, so we can't always just add them up. In what situations can we just add up E nought values...

Neel Bonthala 2G

For part b in question 6N.1, the solutions say that the Nernst equation uses 2 moles of electrons in the redox reaction. However, after going through the problem, only one mole of electron is used in the reaction. Is this a typo in the solutions? Or am I doing something wrong?

Neel Bonthala 2G

Adding a catalyst should increase the rate constant, but according to the Arrhenius equation, decreasing the activation energy should increase k. Using similar logic, increasing temperature increases k according to the equation. Thus, the rate of the reaction should increase.

Neel Bonthala 2G

Hey! When writing the rate, the reactants are always written with negative coefficients because we assume that the reaction is moving forward as time progresses. Thus, the concentration of reactant decreases over time.

Neel Bonthala 2G

I'm in a few different orgs! I'm a part of GlobeMed and Project RISHI, which are both global health organizations but have very different takes on how to approach health. I'm also in HOSA and CaHPSA, which are pre-med orgs. How is GlobeMed? It sounds really interesting! I'm definitely considering a...

Neel Bonthala 2G

Just to echo everyone else, order can only be determined by using experimental data! Technically, each reactant has a particular order in the reaction. The total order of the reaction is the sum of all the individual orders of the reactants. Hopefully that makes sense!

Neel Bonthala 2G

Hey! I could be wrong, but I think we can use the list of redox reactions with their standard reduction potentials as reference to see what the product should be in the half reaction.

Neel Bonthala 2G

I'm in a few different orgs! I'm a part of GlobeMed and Project RISHI, which are both global health organizations but have very different takes on how to approach health. I'm also in HOSA and CaHPSA, which are pre-med orgs.

Neel Bonthala 2G

To add on, you can actually just simplify the second equation to 0.05916V in the numerator. This takes into account all of the constants that are multiplied out at a temperature of 25* celsius. But yes, the first two can be used interchangeably and the last one is used for reactions at equilibrium!

Neel Bonthala 2G

Hey! You would still need to include the HCl because the Cl- ions it provides is a necessary part of the products. You are right that it doesn't directly participate in the redox reaction, but because it's included in the unbalanced reaction, I'm pretty sure we still use it. Hope that helps!

Neel Bonthala 2G

I understand the difference between the two Nernst equations: E = E* - RT/nF(lnQ) and E = E* - 0.05916V/n(log 1), but are there specific situations of when to use a specific one? Or can they be used interchangeably? I appreciate any help!

Neel Bonthala 2G

I understand the equation E = E* - (RT/Fn)lnQ when it comes to the relation between concentration and voltage; however, I am a bit confused as to what the term E* specifically means. How does it differ from the E at the left-hand side of the equation? If someone could clear that up for me that'd be...

Neel Bonthala 2G

Hey! So there is a general trend, although I know there are many exceptions. Because an oxidizing agent ultimately wants to gain electrons, you can use electronegativity as a trend to approximate which oxidizing agent will be the strongest. But of course, if you have access to the reduction potentia...

Neel Bonthala 2G

Hey! So like others said, when a system does work on its surroundings, the work will be negative. This is why in our expansion example problems in class, they were all negative work. Expansion means the system is pushing the piston outwards, and thus doing work on its surroundings. Compression would...

Neel Bonthala 2G

When I think about degeneracy, or at least calculating w, I always think about it as the number of possible states the molecule can exist in raised to the amount that is present. So if there is one mole present, the number of possible states would be raised by avagadro's number: 6.022x10^23 molecules.

Neel Bonthala 2G

By the end of week 7 we should have 35 posts (85 if you had Dr. Lavelle for chem 14A), since we do 5 posts each week :)

Neel Bonthala 2G

I was working through problem 4.19 in the textbook, and the question asked to calculate the kinetic energy of Kr. The solution manual mentions that average kinetic energy = 3/2RT. Where does this equation come from? I see that it's equal to the internal energy of an ideal gas, so do we assume that a...

Neel Bonthala 2G

In the textbook on problem 4D.7, the solution manual uses the temperature 298 K in the ideal gas law equation to solve for work. However, where is this temperature given to us in the problem? The only information given is the chemical reaction and the number of moles reacted. I don't really understa...

Neel Bonthala 2G

Well for one, we would use one over the other depending on the information we have given to us. If we don't know heat of the reversible reaction or temperature, we can't necessarily use the thermodynamic entropy equation. I don't think Dr. Lavelle has explicitly gone over the differences between ent...

Neel Bonthala 2G

I'm not entirely sure, but I don't think there would be a situation where that happens. For each phase change, entropy increases from solid to liquid and liquid to gas, and the only way for these phase changes to occur is for heat to be inputted into the system. Thus, enthalpy must increase as well....

Neel Bonthala 2G

Hey, I have a quick question about delta g and its relation to spontaneity. So on the graph given on #20, the G curve shows a minimum for the reaction in which the reaction always approaches the minimum, which is also the equilibrium, demonstrating that the reaction is spontaneous. If the curve inst...

Neel Bonthala 2G

I thought that we could only use the entropy equation that calculates residual entropy due to changes in volume in isothermal reactions. However, on Sapling Week 5/6, problem #6, we use ∆S = nR lnV2/V1 even though the temperature is changing (not an isothermal reaction). Did I have the wrong assumpt...

Neel Bonthala 2G

When a problem says the reaction is isothermal, do we assume it occurs on a reversible pathway as well?

Neel Bonthala 2G

I'm not entirely sure if Dr. Lavelle went over this in lecture and I missed it, but could someone explain exactly how we derived the equation for the work of an isothermal, reversible reaction? I believe it is w = -nRTln(V2/V1)

Neel Bonthala 2G

I got the right answer, but I don't really understand how to get Cv from Cp. I looked it up, but it's not consistent with the relationship shown on the equation sheet. Can someone help? Here's the problem for reference: "A 0.565 mol sample of CO2(g), initially at 298 K and 1.00 atm, is held at ...

Neel Bonthala 2G

Hey! So, the only reason we have to convert from L*atm to J is just because the problem asks us to give the work in joules. Unless the problem specifies for an answer in joules, it likely won't be necessary to convert!

Neel Bonthala 2G

Hey! So on that problem, at least on sapling, the heat constant is not Cv but Ccal, meaning its the heat capacity of the calorimeter. The heat capacity of the calorimeter takes into account the moles reacting I think, because it measures the amount of heat to increase the temperature of the entire s...

Neel Bonthala 2G

Hey! Yeah, the specific heat under constant pressure/constant volume for an ideal gas should be given in the problem. In the case of the sapling question, it is important to know that Cp = Cv * R, in which R is the ideal gas constant = 8.3145 j/mol*k.

Neel Bonthala 2G

Hey! As everyone mentioned earlier, reversible pathways are when the internal and external pressures are equal, so change only occurs in very small steps. Thus, these reactions take much longer and do more work. In irreversible pathways, the external pressure and internal pressure are not equal, and...

Neel Bonthala 2G

Yes, you're correct! Moles of gas are the only ones doing work when pressure is changed because ultimately the changing concentration of gases is what is affecting the system. Solids and pure liquids don't affect the system through pressure changes.

Neel Bonthala 2G

Hi! Yes, both words are interchangeable.

Neel Bonthala 2G

What do you get when you cut an avocado into 6.022x10^-23 pieces? A guacamole.

Neel Bonthala 2G

When working with acid and base equations, use the Ka or Kb value to determine if x is insignificant. If the equilibrium constant is less than 10^-4, it's probably safe to assume that not much of the initial amount of the acid/base was deprotonated/protonated. However, to be even more careful, there...

Neel Bonthala 2G

Hey! So to find percent protonation, you need both the concentration protonated (BH+) divided by the initial concentration. Essentially, to find the initial concentration of amine, you have to add both the equilibrium concentration (B) and the concentration of protonated amine (BH+). This follows th...

Neel Bonthala 2G

Yeah, there should be a periodic table Dr. Lavelle has on his website that we're allowed to print out and use! We can also use the equation sheet that he has put up.

Neel Bonthala 2G

Exactly! Since solids are not included in equilibrium (you can't really increase the concentration of a solid), they are excluded from equilibrium calculations. So there would be no change.

Neel Bonthala 2G

Hey, yes I think you have to use the reciprocal of the Ka value! Because the reaction involves sodium and propionate, I think you have to use the Kb value instead.

Neel Bonthala 2G

Hey! So from my understanding, compressing the system is the same as decreasing the volume. However, there would be no shift in equilibrium because the moles of gas are equal on both sides of the reaction. Decreasing volume causes the equilibrium to shift in the direction that has fewer moles of gas.

Neel Bonthala 2G

I thought it would be appropriate to link this resource guide from the CPO! This includes more than just academic resources :)
https://docs.google.com/document/d/1AUb ... ZLmKo/edit

Neel Bonthala 2G

The shift just refers to the amount of product formed versus the amount of reactant! A shift to the left means more reactant is formed at equilibrium, while a shift to the right means there will be more product formed at equilibrium instead.

Neel Bonthala 2G

Like those above said, adding substance into the reaction will likely mean it will be subtracted as the reaction proceeds. So after adding in reactant, there should be a negative change as the forward reaction will be favored.

Neel Bonthala 2G

The way I see it, it's the percent of how much of the acid/base actually dissociated in solution. So the lower the percent ionization is, the weaker the acid/base.

Neel Bonthala 2G

Hey! So, by adding NO, you know that equilibrium should shift to the left (NOT the constant). By bringing the concentration of NO to .800 moles, you solve the ICE table with the following initial values: [N2] = 0.200, [O2] = 0.200, and [NO] = .800. Once you determine equilibrium concentrations, just...

Neel Bonthala 2G

Yeah, increasing temperature always favors the side that has greater enthalpy! This is because the added energy has to be used up in the reaction, so it moves away from the side that releases energy (or lower enthalpy, because lower enthalpy means heat was released).

Neel Bonthala 2G

Hey! So I think the main assumptions made in regards to ideal gases is that they have completely elastic collisions, which mean that they don't lose any energy after colliding in a closed space. Additionally, the volume of each molecule of gas is small enough to be ignored in calculations. Finally, ...

Neel Bonthala 2G

I had a similar question after doing the same problem. I'm pretty confident that there must be an error in the textbook, because there is clearly less moles of gas on the product side than on the reactant side. So increasing pressure should favor products!

Neel Bonthala 2G

Yeah exactly! The definition of equilibrium is that the rate of the reverse reaction is equal to the rate of the forward reaction. Thus, the speed at which each reaction occurs should be the same. When one reaction is faster than the other, the reaction is no longer at equilibrium.

Neel Bonthala 2G

Just to clarify, any stresses that result in a change in accordance with le Chatelier's rule do NOT affect the value of the equilibrium constant other than temperature right? So any change in pressure or concentration still cause the equilibrium constant to remain the same value despite the change i...

Neel Bonthala 2G

Just a heads up, radial nodes will NOT be on the final! Just focus on angular nodes--particularly those that exist in the 2p subshell.

Neel Bonthala 2G

So I was working on a Sapling problem and it said "As the number of of oxygen atoms in an acid increases, the strength of the bond with the Hydrogen decreases, and thus the strength of the acid increases". So, it said that in terms of increasing strength, HIO < HIO2 < HIO3 < HIO4. However,...

Neel Bonthala 2G

In lecture, Dr. Lavelle mentioned that salts containing the conjugate base of a weak acid are able to deprotonate water in solution. I understand this is because these conjugate bases are stronger. Is it possible also, however, for salts containing conjugate bases of a strong acid to deprotonate wat...

Neel Bonthala 2G

Today in the Wednesday review session, Dr. Lavelle mentioned that to find covalent character in ionic bonds, compare the electronegativity difference between both cation and anion. However, in a previous lecture, Dr. Lavelle mentioned that the polarizability of the anion and the polarizing power of ...

Neel Bonthala 2G

Yes, It's probably easiest to memorize them. However there are a few ways to tell if an acid or base will be strong or not. Strong acids also tend to have a very large bond length (hydroiodic acid is strong because iodine has a large atomic radius, and thus is far away from the hydrogen). Additional...

Neel Bonthala 2G

Yes, Lewis Acids accept the electron pair! By accepting the electron pair, they use it to form a coordinate covalent bond between the electron pair donor and the proton. I'm not entirely sure if this is unique to an aqueous environment, but I wouldn't be surprised if it was! Remember Dr. Lavelle's e...

Neel Bonthala 2G

Hey! So both HCN and NH4+ are both decently weak acids to begin with, with very similar pKa values, both around 9.2. If you really want to determine which one would be stronger, we would probably use the relative acidity. Someone feel free to correct me, but I think that NH4+ would be slightly stron...

Neel Bonthala 2G

Hey! The coordination number is just the number of bonds between the central transition metal ion and the ligands. Don't worry about any other bonds within the ligand! So from what we've went over in class, the coordination number should be either 4 or 6, as we are only looking at compounds with a t...

Neel Bonthala 2G

Well it depends. If you remember earlier in the quarter, when we first reviewed unhybridized orbitals, we learned that p orbitals have 3 different orientations-- px, py, and pz. Each p orbital was on a different axis. The reason the unhybridized p orbital was perpendicular rather than in plane was b...

Neel Bonthala 2G

On Wednesday's lecture, 12/2/2020, Dr. Lavelle used an example in which HCl in H2O would result in a coordinate covalent bond forming between the Oxygen in water and the Hydrogen in HCl. Would this still occur if the acid was HF, considering there would be a greater amount of dissociation energy req...

Neel Bonthala 2G

Hey! Dr. Lavelle just put up a lot of the synchronous review hours, so I'll be sure to making use of as many of them as I can. I'd spend a lot of time studying the Quantum World because that section will be most prevalent on the final, considering we spent the most time on it. And of course, make su...

Neel Bonthala 2G

Yes, you're completely correct in that size contributes a lot to how strong a bond is. Larger radii means larger distance between nuclei, which creates a bond that is easier to break. Also, bond order is extremely important in determining bond strength. Triple bonds are a lot stronger than double b...

Neel Bonthala 2G

Yes, the shape is just called bent. Bent can also result from a molecular geometry of 3 regions of electron density, and one lone pair! The bond angles will be different between these two configurations of the bent shape though.

Neel Bonthala 2G

Yes, you're completely correct in that size contributes a lot to how strong a bond is. Larger radii means larger distance between nuclei, which creates a bond that is easier to break. Also, bond order is extremely important in determining bond strength. Triple bonds are a lot stronger than double bo...

Neel Bonthala 2G

Do all molecules with resonance structures have unhybridized molecules that contribute to delocalization of electrons? In the benzene example in lecture, each C in benzene had 3 hybridized orbitals, but then it had 1 unhybridized p orbital that contributed to its resonance. What exactly is the model...

Neel Bonthala 2G

Hey! I had a pretty similar question myself because it seems like a pretty non-descriptive term. But from my understanding, I think a delocalized pi bond shares electrons across the molecule like in the benzene example Dr. Lavelle showed us in lecture. Thus, the electrons present in the orbitals tha...

Neel Bonthala 2G

Yes, I think Dylan is correct! It's important to know the order of increasing distortion between regions of electron density. Lone pair-lone pair > lone-pair-bonded pair > bonded pair-bonded pair. So at least know that trigonal pyramidal has a slightly smaller bond angle than tetrahedral due to the ...

Neel Bonthala 2G

Hey Anil, if the problem is not assigned on the syllabus, then I doubt we need to know it for this class. I checked the syllabus and 2F.19 was not assigned, and neither of those terms are in the required objectives that we need to know, which are outlined on Dr. Lavelle's website. So I'm guessing th...

Neel Bonthala 2G

Hey! Definitely take advantage of as many workshops and synchronous hours that Dr. Lavelle has created before the final. Like everyone else said, going through homework seems like it'll be super important as well. I suggest reviewing all of the objectives that are on Dr. Lavelle's CHEM 14A website! ...

Neel Bonthala 2G

One of the objectives on the outline for Chemical Bonds is "Explain how covalent bond dissociation energy is related to covalent bond multiplicity, atomic radius, and the presence of unpaired electrons." I understand how covalent bond dissociation energy is related to covalent bond multipl...

Neel Bonthala 2G

After doing some problems in the textbook, I noticed that some Lewis Structures with a total charge have only one bracket indicating charge. Why is there only one bracket used instead of two? What does it mean when there is only a bracket on one side? This is seen in the answer solution to 2B.5. Tha...

Neel Bonthala 2G

Also, remember to get tons of sleep beforehand! Being well rested is a huge part of being prepared -- which will definitely reduce test anxiety. I like to always wash my face before my exam, because I feel fresh and ready to take on the exam, and it also wakes me up.

Neel Bonthala 2G

Hey! So in hydrogen bonding, a hydrogen attached to an electronegative atom creates a hydrogen bond with either an N, O, or F atom in another molecule. Do these atoms (N, O, F) also have to be attached to another atom that is significantly different in electronegativity? So, a hydrogen bond cannot f...

Neel Bonthala 2G

Hey! So not using molecular geometry, one way polarity can be determined is by comparing electronegativities. If there are two atoms in a molecule with a large difference in electronegativity, it is likely to have ionic characteristics and would thus be polar. For example, in a water molecule, H and...

Neel Bonthala 2G

Hey! So just to add on, the first 4 elements on the periodic table are all exceptions to the octet rule. Hydrogen, Helium, Lithium, and Beryllium don't have a p subshell, so they only have 2 orbitals rather than a full 8.

Neel Bonthala 2G

Today in lecture, Dr. Lavelle used the interaction between two HF molecules as an example of a dipole-dipole interactions, as the slightly negative Fluorine interacts with the slightly positive Hydrogen. Dr. Lavelle mentioned that on average, these interactions release about -2 KJ/mol. However, isn'...

Neel Bonthala 2G

Also, it's important to note that when it comes to electron configurations, we don't even have to know energy levels past 4p!

Neel Bonthala 2G

Hey! I got Ca, Mg, and Al instead actually. 1) So I believe Ca would have the lower ionization energy because its electrons are much more shielded than Mg, even when two electrons are removed. This is because Ca is a whole energy level higher than Mg (n=4 vs n=3). 2) Mg would have the lower ionizati...

Neel Bonthala 2G

It's also important to note that because metals give up an electron and nonmetals gain an electron during ionic bonding, they gain charges! But in covalent bonding, while there might be shifts in polarity, the atoms involved are not ionized. Some common differences between ionic bonds and covalent b...

Neel Bonthala 2G

In textbook number 1D.25, the question asks whether it is possible for the subshell 6f to exist. From my understanding, the periodic table only goes up to 5f as a subshell, yet the solutions say that 6f is a possible subshell. So my question is, can subshells that exist past the known elements in a ...

Neel Bonthala 2G

So to my understanding, in resonance structures, electrons that form double bonds are delocalized because they exist in multiple locations (equivalent electron density). But does this mean electrons involved in single bonding and lone pairs are not delocalized? Or are they also equally shared among ...

Neel Bonthala 2G

After looking through trends in the periodic table in the lecture on 10/28, I came across something I don't quite get. I understand the fundamental difference between the two: ionization energy involves removing the outer-most electron of an atom in a gaseous state, while the work function is the en...

Neel Bonthala 2G

Hey, what the others said is completely correct. Just for the sake of clarification, the model of light can be considered as a wave in other experiments, and is even proven by the c = λ ν equation. The equation works for the wave model because as frequency decreases, wavelength increases at an inver...

Neel Bonthala 2G

Hey! So I had a similar question and after some digging around I think the major difference between atomic and molecular spectroscopy is the energy levels. In multi-electron systems, which are used in molecular spectroscopy, each subshell has a different level of energy due to a combination of elect...

Neel Bonthala 2G

For multi-electron systems, are we required to know how to calculate the effective nuclear charge for the nucleus? During the lecture on 10/23/2020, Dr. Lavelle said that the nuclear charge of Lithium was 3+, and its effective charge was between 1+ and 3+, but I wasn't entirely sure how that range w...

Neel Bonthala 2G

Going through the learning objectives in the Quantum World outline, I found the following objective: "With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic...

Neel Bonthala 2G

Hey! So ionization just means that the atom has become an ion, or lost/gained electrons and now has a charge. In this case, the ionized form of Oxygen has a charge of -2. This means that oxygen has 2 extra electrons. As a result of the greater number of electrons in its shell, the electrons repulse ...

Neel Bonthala 2G

I'm also confused about the Schrodinger Equation... When Dr. Lavelle says that we operate a change on the wave function, is that operation always a hamiltonian? Because at the bottom of the equation sheet there are a few formulas involving the wave function that I just don't understand... If someone...

Neel Bonthala 2G

I think that one electron only emits one photon of a given energy level. From my understanding of the photoelectric experiment, one photon can only eject one other electron, because this energy can only be absorbed by a single electron. I would assume this same principle applies as the electron fall...

Neel Bonthala 2G

Hey! So for the electron, we can find its energy using the kinetic energy formula, E_k = 1/2 * m * v^2. Because the electron is a moving object, its energy is kinetic and can be calculated by knowing its mass and velocity. The mass of an electron is given to us as 9.11x10^-31 kg. The velocity can be...

Neel Bonthala 2G

Personally, I've been studying mainly through textbook problems, especially because those types of problems will be put on future exams. Additionally, UA workshops are SUPER helpful for additional practice. Even if I can't make it to live sessions, I always try to do the worksheets posted on the sha...

Neel Bonthala 2G

All of these replies are correct, but I just want to add on a note to keep in kind. When dealing with equations like (wavelength)(frequency) = c, make sure that wavelength is in meters, as that's the si unit that is used in this calculation. Other than that, yes, your answer can either be in m or nm...

Neel Bonthala 2G

Hey! Just to add onto the explanations, the energy gaps get progressively smaller because as the electron is further away from the nucleus, there is less of a magnetic force pulling it towards the positively charged center. Because electrons are negatively charged, it is usually very difficult, and ...

Neel Bonthala 2G

From my knowledge, the electrons are simply ejected from the metal's surface and actually collide with a detector or some other tool to measure the velocity, ultimately being used in kinetic energy calculations. Looking at diagrams of the experiment, there's a battery that establishes a negative cha...

Neel Bonthala 2G

Hi! So technically, the energy to remove the electron IS the work function. The work function is essentially the threshold energy. And if the kinetic energy of the electron is 0 J, then this work function or threshold energy will be equal to the energy of the photon hitting the surface of the metal....

Neel Bonthala 2G

Hi, I'm struggling to go about this problem in the post module assessment. In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does the lamp generate in 1.0 s...

Neel Bonthala 2G

Hey! So finding the molar masses of the reactants and products requires you to actually know a little about how to read line drawings, which are pretty common in organic chemistry. Basically, its just a way to represent carbons and hydrogens. Every "vertex" between the lines represents one...

Neel Bonthala 2G

Could someone explain why you do 5-4 in order to get the moles leftover of the excess reactant? Hey! So you subtract 4 moles from the 5 moles of excess because 4 moles is the amount that reacts with the limiting reactant in the reaction. The 4 is calculated using molar ratios as the person above sa...

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