CHEMISTRY COMMUNITY

Justin Bui 2L

You also don't have to reverse the equations because you're comparing all 3 of their reduction potentials. When reversing the equation and flipping the sign, you're not looking at its reduction potential anymore but its oxidation potential and you can't compare that to the reduction potentials of th...

Justin Bui 2L

I guess it depends on the equation you're looking at because the one with delta G = delta H - T x delta S, the units of G would be H(j/mol) - T(K)S(j/mol.K) and would result in j/mol

Justin Bui 2L

I agree with Justin and you have the right idea. The reaction needs to be spontaneous for it to run, so that means delta G needs to be negative, which is the opposite of what's provided.

Justin Bui 2L

For this problem, the detachable sheet with the reduction potentials is handy to have because it will tell you V, and that will help you determine which half reaction will be reduction/oxidation. This is because you want your Ecell to be positive, so you would want Ecathode to be more positive than ...

Justin Bui 2L

Yes, the moles isn't referring to moles of a certain element but just the number of electrons transferred.

Justin Bui 2L

Yeah, n=4 and that refers to electrons moved because this type of n is a pure number and not moles.

Justin Bui 2L

Yeah, you just generally want to try to make the Ecathode - Eanode a positive number because then it will proceed spontaneously and that's what you want your cells to do. So just see the V when looking at the reduction potentials and reverse the right equation so that you can try your best to keep E...

Justin Bui 2L

So I think what you need to do is look on the detachable sheet that contains all the reduction potentials and look for the ones that apply to O3/O2,OH- and O3,H+/O2. Then, based on what the reduction potentials are, you can decide which half reaction should be the cathode/anode because you want the ...

Justin Bui 2L

I think based off of someone else's question on their test 2 #1, I saw that C is indeed 4+ once in CO2 and the reduced species is oxygen because it goes from 0 in O2 to -2 in CO2

Justin Bui 2L

The C in O2 is 4+ because the O is 2-, but the overall charge is 0, so 2 x -2 would mean C needs to be +4. And O2 is reduced because O in O2 has 0 charge but in CO2 it has a 2- charge, meaning it was reduced.

Justin Bui 2L

Yeah, for the whole shebang in a basic solution, you first balance O with H2O, also, you need to add H2O on the side that needs H, and then OH- on the opposite side

Justin Bui 2L

They're "interchangeable" in the sense that you can choose to use log or ln but they're right in saying there is a difference in how you use each one, so you can't just substitute one with the other plainly. ln(X) = 2.303log(X) is the biggest thing to remember when deciding which path to t...

Justin Bui 2L

It all depends on what is available to you and then with that, you'd be able to decide what to use. But there's usually a chemical equation or steps when it's a difference of sums situation.

Justin Bui 2L

For b), you would use delta S = q/t except you know the interior is warmer than the exterior, so the fraction for the exterior will be bigger due to the smaller denominator. So for that reason, you know the change in entropy would be greater for the exterior than interior.

Justin Bui 2L

where did the time in time x t come from?

Justin Bui 2L

I agree with Lily when she says that the main takeaway from the second law is that delta S total is always increasing and not 0 or decreasing. And yes, for spontaneity, you have to check delta H enthalpy and temperature as well to be sure about whether or not a process will be spontaneous.

Justin Bui 2L

Yeah, I'd say it's safest to check it through Gibbs free energy just because the sign of delta G would be able to tell you for sure whether or not something is spontaneous and it's the combination of multiple things apart from just delta S.

Justin Bui 2L

Yeah, I agree with what Diane said but I feel like it being completely false is a little unfair of a generalization. I think a lot of the time delta S happens to be positive so it is true that an endothermic reaction is favorable at high temperatures but it is true that negative entropy would throw ...

Justin Bui 2L

I also was wondering the same thing, where delta G would still be negative (spontaneous) even if delta S were negative, as long as the reaction was exothermic enough (delta H is a large negative).

Justin Bui 2L

8.9 An ideal gas in a cylinder was placed in a heater and gained 5.50 kJ of energy as heat. If the cylinder increased in volume from 345 mL to 1846 mL against an atmospheric pressure of 750. Torr during this process, what is the change in internal energy of the gas in the cylinder? Apart from findin...

Justin Bui 2L

Can someone give me a concise explanation of what standard means? Or when Delta G has that little degree sign following it. This also shows up in other formulas.

Justin Bui 2L

What does a cell look like and are there any rules for how they're drawn out?

Justin Bui 2L

What's the list of steps that help us balance redox reactions more easily?

Justin Bui 2L

Yeah, seems like we often don't have to memorize a lot of things just for the sake of memorizing them. Instead, we're given pieces and necessary info: the enthalpies and reactions to reach the final reaction and get its enthalpy and that demonstrates our understanding.

Justin Bui 2L

We would also be told the conditions of the problem and then we would know which one to use, Cp or Cv, based off of that.

Justin Bui 2L

Stability is an indicator of how strong bonds are because the more stable something is, the more resistant it is to perturbations. So strong bonds should be able to withstand or require more energy in order to break them.

Justin Bui 2L

Yeah, since the equation of q in the system is closed, the sign's position really just depends on whether the reaction is exo or endothermic.

Justin Bui 2L

Yeah, I agree with the people above. Memorizing heat capacities or just numbers outright isn't a proper indicator of our understanding of the material or at least I'd hope so.

Justin Bui 2L

Will we have to commit any substances' standard enthalpies of physical change to memory? (table 8.3)

Justin Bui 2L

What type of system would you say a fish tank is? It's "closed" but things still go in and out technically but I'm not too sure.
Help!

Justin Bui 2L

I think it asked if Glycine or an amino acid like it was amphiphoteric. What was it?

Justin Bui 2L

For the question, it gave us grams of CO2 and grams of H2O produced and, from that, find the empirical formula of the CHO compound. Just to clarify, did ya'll find grams of C through CO2 and then H from H2O and then find grams of O from the total CHO compound?

Justin Bui 2L

For clarification, there has to be a sigma bond before a pi bond, and there only has to be 1 sigma bond for something like a triple bond, correct? In a triple bond, there is a sigma bond and 2 pi bonds?

Justin Bui 2L

At what point in the periodic table do expanded octets become a possibility and why?

Justin Bui 2L

Which of the following ligands can be polydentate? If the ligand can be polydentate, give the maximum number of places on the ligand that can bind simultaneously to a single metal center: (a) HN(CH2CH2NH2)2; (b) CO3 2-; (c) H2O; (d) oxalate.

Justin Bui 2L

Can someone explain to me again how the relationship between equilibrium of a reaction and its reverse reaction is inverse?

Justin Bui 2L

What are the naming conventions for complexes and coordination compounds and what are some good ways to remember them?

Justin Bui 2L

How come lone pairs of electrons change bond angles, and do opposite lone pairs of electrons offset each other?

Justin Bui 2L

I also recall reading somewhere that starting after Phosphorus, since it and the elements in its family/family to the right are large atoms, it is possible for them to have expanded octets as well.

Justin Bui 2L

What was the structure of HOCO for the midterm and was it a radical?

Justin Bui 2L

I agree, knowing the radius to an accuracy of 1% means that the uncertainty in position is a hundredth of what the radius is, which is multiplying the radius by 0.01 or dividing by 100. Then, you can use that as delta x in the heisenberg equation and finish

Justin Bui 2L

HCL has higher ionic character because CL has higher electron affinity than I and will consequently take H's electron in a way that gives it greater ionic character

Justin Bui 2L

Yup, I did the same thing as ^^ and I think it's because 1/2mv^2 describes best the energy of the moving electron while DeBroglie's equation also uses velocity but it's moreso for waves/light

Justin Bui 2L

What are the shapes of the orbitals and why is that important and do you think we will need to know that for assessments?

Justin Bui 2L

In lecture, we went over the first row of transition metals and at Chromium and Copper, there's the d5 and d10 exception. Do those exceptions work exactly the same for the elements in Chromium and Copper's respective groups as well?

Justin Bui 2L

For the magnetic quantum #, (ml), how do I know which number to use?

Justin Bui 2L

Yeah, I agree. In lecture, Lavelle said he'd be providing constants and things that would be necessary just like how a periodic table was necessary for the first test and one was provided to us.

Justin Bui 2L

Yup ^^ and because of that, you can also technically look at wavelengths with longer wavelengths having lower radiation and shorter wavelengths with higher radiation

Justin Bui 2L

I think it would be safer to keep a lot of sig figs (more than 3 in your example) and then at the end, round it to 3 sig figs so that the calculations will be as accurate as possible. Sometimes it might not make a difference but it is more accurate.

Justin Bui 2L

For part A of M11, am I supposed to use the amount of oxygen leftover from the first reaction in the second reaction or am I supposed to use the starting mass of oxygen for the second reaction to see if O2 is a limiting reactant?

Justin Bui 2L

A molecule of human DNA was found to contain 2.1 x 10^9 atoms of carbon. Calculate the chemical amount (in moles) of carbon atoms in the molecule of DNA.

I know there's a relationship between number of atoms in a mole with Avogadro's number but I'm not sure how to use it exactly.

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