CHEMISTRY COMMUNITY

Daniel Chen 2L

But doesn't the concentrations of the reactants and products in a concentration cell have to be different in order to generate voltage?

Daniel Chen 2L

One of the main things that a catalyst does is change the amount of work that a system does.

Daniel Chen 2L

I think it's that a catalyst directly affects one step of a reaction, but has an effect on the entire reaction as a whole.

Daniel Chen 2L

We also discussed how to approach proposed reaction mechanisms with multiple steps.

Daniel Chen 2L

So basically what you are saying is that a decrease in temperature will decrease the rate of an exothermic reaction?

Daniel Chen 2L

They are both correct, but it's a lot more preferred to have it written out in the provided formula that's given "-1/a d[A]/dt = 1/b d[B]dt = 1/c d[C]/dt"

Daniel Chen 2L

I think that he said that we could?

Daniel Chen 2L

If the reverse reaction is favored and k' is the constant for the reverse reaction, shouldn't that one increase as well? I mean, I know it's a constant, but since the temperature has an effect on k then it should change right?

Daniel Chen 2L

The variable A is the frequency or the pre-exponential factor.

Daniel Chen 2L

I like to think that the rate of consumption has to do with the rate of the slowest step of the reaction rather than the concentration of ammonia.

Daniel Chen 2L

I get that Q is [products]/[reactants] but why, for galvanic cells, is it anode/cathode?

Daniel Chen 2L

I don't remember learning this in class? Is this in any of the textbook sections that we have for homework?

Daniel Chen 2L

If it has the naught then that means it is at standard conditions. I think you can use the equation just fine not at standard conditions, you just have to do it without the naught?

Daniel Chen 2L

Would it not be better to just include the unit in your calculations? I'm not too sure if you can just leave it out or not.

Daniel Chen 2L

Can someone explain to me how concentration cells are different from the regular galvanic cells we learned about in class? Also, why is the standard cell potential 0 in these types of cells?

Daniel Chen 2L

Is the general topic of Test 2 going to be Gibb's Free Energy and Electrochemistry?

Daniel Chen 2L

Can redox reactions happen with the reactants and products in their gaseous states, and can water still be used to balance the reaction?

Daniel Chen 2L

The part of the redox reaction that is the reduction half-reaction is the one that gains the electron. If you remember the term OILRIG, then you'll be alright (Oxidation is Lose, Reduction is Gain).

Daniel Chen 2L

There can also be acidic and basic redox reactions. So that's why there may be H+ ions?

Daniel Chen 2L

In class we learned about two different equations, that kinda gave the same answer for some of the cell potential questions. But they aren't different methods for the same thing, are they? Aren't they equations for different things?

Daniel Chen 2L

In general, you just add the charges up of all the elements in the compound and you should get the total charge.

Daniel Chen 2L

By the way, it's not meant literally, but figuratively. He separates the reaction equation into parts so that it would be easier to understand.

Daniel Chen 2L

Free elements have an oxidation number of 0 though, right?

Daniel Chen 2L

Is "oxidation number" the number that is assigned to an element because it's missing a certain amount of electrons to reach an octet, or is it only used for when elements are oxidized in redox reactions?

Daniel Chen 2L

I don't think you have to do it this way, but it makes things a lot easier to see and understand.

Daniel Chen 2L

Usually, the heat capacity of a Calorimeter is already known, so that way scientists can use them to find the heat capacities or other factors of the materials placed in them.

Daniel Chen 2L

Does this mean that making a large error in W, will make a small error in S? How do they correlate with each other?

Daniel Chen 2L

Degeneracy was talked about in the lecture. I think it was the lecture about the number of possible positions for a molecule or something like that.

Daniel Chen 2L

The denotation from Standard Residual Entropy is W, right?

Daniel Chen 2L

The Delta S for formation is 0 because they are already in their standard states. That's how they are found in nature. Trying to find the change in entropy for the formation of standard states from their standard states, is like trying to change something into the thing they already are, like trying...

Daniel Chen 2L

I'm not really sure I can explain this all that well, but it's something along the line of this: You're trying to form the standard state of something from something, yes? So the energy from that is the standard enthalpy of formation. For a substance like O2 gas, which is the standard state of its e...

Daniel Chen 2L

Another silly example, that I had once done in high school I think, was a double-layered foam cup. It was very crude, but it got the job done.

Daniel Chen 2L

So if the pressure of the system is not constant, then the formula is reversible?

Daniel Chen 2L

An example that Dr. Lavelle gave us in class between the difference between the closed and isolated systems is that typically the isolated system is insulated. This way, since the system is insolated, it can't transfer energy with its surroundings. A closed system is, however, not insulated. That me...

Daniel Chen 2L

Since the beaker is an open system, you can assume that the pressure is whatever the atmospheric pressure is. Unless you are somehow constantly changing in elevations or something else, I think you can otherwise assume that the pressure is constant?

Daniel Chen 2L

So are you saying that the standard reaction enthalpy is 0 when a reaction does not occur under standard conditions?

Daniel Chen 2L

Is this a homework problem that we have to do?

Daniel Chen 2L

I kind of just think about it as the standard enthalpy is when the system is in standard conditions or something. Like when everything is kept constant and is managed. That's what we learned in LS 7A at least.

Daniel Chen 2L

The release of energy on the skin is largely different and that's what causes the burns since it's so much larger for steam.

Daniel Chen 2L

Have we learned about how heat, work, and internal energies respond to these yet?

Daniel Chen 2L

Isn't the Ka for water is 1.0 * 10^-7 at 25 degrees Celsius?

Daniel Chen 2L

Could you not just convert the mmol values to mol so you can calculate the concentrations that way?

Daniel Chen 2L

Is this also the situation in which you can approximate the calculation in the ICE table if the K value is less than 10^-3 or am I thinking about something else?

Daniel Chen 2L

It's definitely possible for this to happen! One of the practice problems that I had been doing in my discussion had a problem like this. In this case, you should check whether the values you got are possible. For example, for the problem that I did, of the equilibrium molarity values that I receive...

Daniel Chen 2L

It's also possible that there will be problems that ask for certain initial concentrations or pressures and you're given the equilibrium concentrations and pressures. You can use an ICE table to solve for those as well.

Daniel Chen 2L

When Q is less than K it means that the reaction hasn't gone all the way through yet, and is not at equilibrium. It is more shifted to the right side.

Daniel Chen 2L

I think it's the fact that it isn't just a change of pressure will change whether a reaction will be forward of in reverse, it's more of how has the pressure changed and if there are any other modified factors.

Daniel Chen 2L

Will we be expected to sometimes use the approximations, or will we be able to just to use the quadratic formula instead?

Daniel Chen 2L

I think these topics will be touched upon later on when Dr. Lavelle decides to lecture about Kinetics. Not too sure though.

Daniel Chen 2L

If you later find that you're wondering about the difference between Q and Kp (pressure, rather than Kc, which is concentration), then you can just come back here because it's pretty much similar, I think.

Daniel Chen 2L

So is the Ideal Gas Law used for reactions with gasses only, or is it more specific than that?

Daniel Chen 2L

Yes, basically you just need to memorize the list of strong acids and bases. The UAs said that if an acid or base isn't a strong one, just immediately assume that it is a weak acid or base.

Daniel Chen 2L

Yes, you can write the abbreviations for the compounds. As for what Dr. Lavelle prefers, I'm sure he's okay with using the abbreviations if he allows it for the test.

Daniel Chen 2L

It's formed with a platinum atom as the central atom and two chlorines on the same side and then two ammonia molecules on the other side.

Daniel Chen 2L

You change it to bis-, tris-, and tetrakis- for polydentate so that it's emphasized that it is a polydentate complex.

Daniel Chen 2L

I'm not too sure, but I'm just assuming that that's just something you have to memorize. You don't have to currently know too much though.

Daniel Chen 2L

Don't amphoteric compounds include those atoms from the periodic table that are just left of the metalloid diagonal line?

Daniel Chen 2L

I think organometallic complexes are just coordination complexes with carbon in them? I'm not too sure about this.

Daniel Chen 2L

Apparently carbonate is normally monodentate, but it can also bind to two different metals?

Daniel Chen 2L

I'm pretty sure "Ox" is not EDTA. I think it was the abbreviation for an oxalate ion.

Daniel Chen 2L

I think vitamin b12 was just a biological example that he was giving. I don't think we have to specifically know too much about it.

Daniel Chen 2L

I don't think we need to factor the prefixes for the atoms in the alphabetization of the naming, do we?

Daniel Chen 2L

I don't think we have gone over this in class yet, so maybe we can wait and see? He might go over it in lecture, not too sure.

Daniel Chen 2L

I think that for an organometallic complex to be organic it has to have a Carbon in it.

Daniel Chen 2L

I didn't realize that it was uncommon for coordination compounds to be negative. Are they not typically negative?

Daniel Chen 2L

Are you talking about when drawing the Lewis Structures? I think you can just draw the Lewis Structures how you would normally.

Daniel Chen 2L

Lone pairs are only supposed to be on the equatorial positions because those are the most stable I think.

Daniel Chen 2L

I think you're supposed to look into the specific shape of the different central atoms and their surrounding atoms?

Daniel Chen 2L

The repulsion forces and bond angles are different for equatorial and axial. Axial has two repulsion forces since it's two ends of an axis. Equatorial may have 3 or more repulsion forces.

Daniel Chen 2L

It's pretty much memorization though. I mean, if you find the shape of the molecule, you can draw it out and then get the angle from there?

Daniel Chen 2L

Daniel Chen 2L

If breaking a bond requires energy then is energy gained to break the bond and the energy is released when the bond is broken???

Daniel Chen 2L

Water is able to dissolve those ionic molecules because the attraction between the positive and negative parts of the water and the other molecule is able to separate the separate atoms of the ionic molecule from each other.

Daniel Chen 2L

It isn't always between just a single bond and a double bond since there can also be triple bonds, but basically it's just an average length between all bonds.

Daniel Chen 2L

But are we able to turn in homework from the Topic 2 section still?

Daniel Chen 2L

I'm pretty sure there is a range of Hydrogen bonds attractive force, but it isn't always -20 kJ/mol.

Daniel Chen 2L

You probably don't have to memorize the electronegativity of every single element on the periodic table, but you can remember that Fluroine (F) is the most electronegative (4) and Francium is the least electronegative (0.7). Reminder: electronegativity increases as you go across a period from left t...

Daniel Chen 2L

If you can recall from the lecture, the difference in electronegativity between the two atoms that are bonded can usually tell you when the bond is covalent or ionic. When the difference in electronegativity is > 1.5, then the bond is covalent. When the difference in electronegativity is < 2.5 then ...

Daniel Chen 2L

An example of when this formula would be used is when a question asks something like, an electron moves from n=3 down to n=1. You'd calculate that difference of energy with delta E (E final - E initial). To calculate this you use that formula and plug in the values of n, in this case 3 and 1.

Daniel Chen 2L

I don't think the d-orbital counts as an orbital which has valence electrons? Typically valence electrons are in the s and p-orbitals, which is why the transitions metals will have their valence electrons in the s-orbitals (2 e-).

Daniel Chen 2L

Coordinate covalent bonds form when an atom gives a lone pair of electrons to a bond. I can't give an example of one forming in nature at the moment, but coordinate covalent bonds are as strong as other covalent bonds.

Daniel Chen 2L

In response to your second question, the electrons in the d-orbital actually shield poorly, so it would not increase electron shielding.

Daniel Chen 2L

So for example, in the p-orbital, the first 3 electrons are up spins and the last 3 are down spins. So the first 3 are +1/2 since they are up spins and the last 3 are -1/2 since they are down spins.

Daniel Chen 2L

It would be nice if there were more video modules for the other topics that we would be covering the future too. I like to use those for review and also watch them before the lecture for previews, so they really help. Honestly, there are times when I forget what is said in the lecture, or I just don...

Daniel Chen 2L

Yes, it is typically the least electronegative atom that goes in the middle. In addition, Hydrogen atoms are never in the center.

Daniel Chen 2L

In Chemistry 14A, I think it was mentioned that we won't be going past the d orbital. I'm pretty sure we are only going up to the first line of the d-block?

Daniel Chen 2L

Usually what I do to really make myself feel prepared is a series of specific steps. Professor Lavelle usually tells us what we are going to be covering in the next lecture so to prepare for that I usually first read the section in the textbook and look over and do the example problems. After that I...

Daniel Chen 2L

Um, I think that this question is a lot more specified then what we covered so far in our lectures. We so far went up to Pauli Exclusion principle (which is what the previous comment was explaining), but maybe you can ask Professor Lavelle after a lecture?

Daniel Chen 2L

I'm pretty sure that we don't need to mathematically determine the x, y, and z, but when writing electron figurations like the 2p orbital, it goes in the order of x, then y, then z.

Daniel Chen 2L

The different orbitals like p, d, and f have different planes and I think they are just different types of orientations of the electron.

Daniel Chen 2L

I think it might also have something to do with the positioning of the electrons and it being farther away (outer shell) making it easier to react with something else and stability?

Daniel Chen 2L

If you read through the section of the textbook regarding atomic spectra, there are examples given walking you through how to do different problems regarding the topic. I'm sure the homework problems will be similar to something like those.

Daniel Chen 2L

I remember during the lecture Professor Lavelle did say that the electron could go infinitely away from the nucleus. The energy would, however, be zero. He did say that would be our reference point though. So I'm not exactly sure about a limit.

Daniel Chen 2L

Because photons are quantized, no matter how much you intensify the light of a low frequency, the amount of energy per photon will not increase. All you would be doing is emitting more and more photons. That's why even if you release low intensity but high-frequency light, electrons can be removed f...

Daniel Chen 2L

And remember! As said during the lecture, anything beyond X * 10^-15 is the limit for what would be too small of a wavelength to be recognized. For example, a baseball had 10^-34 and a car had 10^-38, which is way too small to be measured.

Daniel Chen 2L

Yes. Basically all electromagnetic radiation travels at the speed of light, but only in a vacuum. If it were in different circumstances then it could be different since other molecules would interact with thee electromagnetic radiation.

Daniel Chen 2L

For the equation that you presented, it should be 2 moles of K to 1 mole of H2. Therefore if you're doing some sort of conversion with this it should be (2 mol K)/(1 mol H2). It depends on what you're trying to find though since H2 is different from H. Obviously H2 is a molecule of 2 Hydrogens put t...

Daniel Chen 2L

If it makes it easier for you, you can try to turn the decimal into a fraction and then multiply all the numbers by the denominator. For example if you had the decimal 1.33, the fraction of that should be 4/3 so just multiply all the numbers by 3.

Daniel Chen 2L

Usually, when doing the calculations, I try to keep all of the numbers as exact as possible. It's when I get to the end of the problem I try to round it to the significant figures. The teaching fellow for my discussion said that we shouldn't have to worry about it too much right now though. As long ...

Daniel Chen 2L

Scientific notation is basically a way of writing a number that's too big or too small in a more convenient form. For example, if you have a large number like 145,000,000, you can simplify this into 1.45 * 10^8. Or, if you have a small number like 0.000000145, then you can simplify this into 1.45 * ...

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