CHEMISTRY COMMUNITY

Varsha Sivaganesh 1A

n is the coefficient for the number of electrons in the balanced equation!

Varsha Sivaganesh 1A

If external pressure is constant then you can use the irreversible equation. In addition, the reversible equation is theoretical, so in most "real world" situations, I feel like it's more likely that we would have to use the irreverisble equation.

Varsha Sivaganesh 1A

I don't think so... at least we wouldn't have to know them??

Varsha Sivaganesh 1A

I wouldn't necessarily describe this situation as having an "optimum" activation energy. Think of it as, if there is enough energy supplied, then the reactants can reach the activation energy which means they have enough energy to break bonds so that the reaction can occur. If activation e...

Varsha Sivaganesh 1A

No, it cannot be negative.

Varsha Sivaganesh 1A

It will cover all of those chapters and I think Dr. Lavelle was saying that the amount of material from a certain chapter that is going to be on the test depends on how much time we spent on it in class. For example, since we breezed through electrochem pretty quickly, it probably won't be the subje...

Varsha Sivaganesh 1A

^ I agree with them, but if what you're asking is if we need to know that for this week's test, I believe the answer is no. We do not need to know anything past 15.6 (I think that means we don't need to know what Dr. Lavelle taught on Friday)

Varsha Sivaganesh 1A

I feel like since the tests are usually more straightforward than midterms and finals, we probably won't have to derive an equation. However, Dr. Lavelle did spend a lot of time going over the derivations in class so I guess it wouldn't hurt knowing how to do them just in case!

Varsha Sivaganesh 1A

Yes, when looking at a table you would first make sure the concentration of the reactant you are looking for is the only one changing between two experiments. If the concentration of the reactant changes and the rate does not change, then you know it is 0 order because the concentration of that part...

Varsha Sivaganesh 1A

I think you are getting K confused with k. K is the equilibrium constant. k, what we are using in this section, is the rate constant of just the forward reaction.

Varsha Sivaganesh 1A

Since we are calculating the rate of the forward reaction, we are assuming that the reactants are being used up and converted into the products. Therefore, the concentration of reactants is decreasing and the change in concentration will be negative.

Varsha Sivaganesh 1A

can a nonspontaneous and spontaneous reaction have the same reaction rate? Possibly? Like if something was added to make the nonspontaneous reaction occur, I don't see why the rate couldn't be the same as that of a spontaneous reaction. I'm not sure if this is correct but that's how I would think o...

Varsha Sivaganesh 1A

I would use 273.15 on the midterm just to be safe... There's nothing wrong with using a more precise number in your calculations!

Varsha Sivaganesh 1A

Aya Shokair- Dis 2H wrote:
Varsha Sivaganesh 1A wrote:Also, when the reaction is irreversible, $\Delta$ S_surroundings = 0.

I don't think that's true.

Oh, I have that in my notes from a TA-led review session... maybe I misunderstood what he was saying then.

Varsha Sivaganesh 1A

Also, when the reaction is irreversible, $\Delta$ S_surroundings = 0.

Varsha Sivaganesh 1A

Bar does correspond to pressure. But I think it's because since there is less pressure, we may be able to assume it is because the volume is greater.

Varsha Sivaganesh 1A

The question says to "assume ideal behavior," so I think that means you assume there is 1 mol of gas!

Varsha Sivaganesh 1A

If a reaction is spontaneous (\Delta G is negative), that means that the forward reaction is favored. Just remember that this does not mean the reaction will happen quickly, it just means that if you leave the reaction alone, it will complete by itself. So if the forward reaction is non-spontaneous ...

Varsha Sivaganesh 1A

I would try to remember how to derive the equations Dr. Lavelle shows us, because not only is it possible that it'll be on the test, but it really helps you with understanding the concept and remembering how all of the things we are learning about are related to each other.

Varsha Sivaganesh 1A

The reason why we set \Delta G° = 0 is to find out the temperature that the Br2(l) is in equilibrium with the Br2(g). The answer we got for T was 333K. So yes, at 333K, the temperature is at equilibrium and neither the forward nor reverse equation is favored. However, when T > 333K, the forward proc...

Varsha Sivaganesh 1A

\Delta G° is the change in Gibbs free energy at the standard state, meaning at either 1 atm or 1 M. Also, I think that when \Delta G° = 0, the reaction is still at equilibrium... In the example we did in lecture with the Br2(l) turning into Br2(g), we assumed that equilibrium was when \Delta G° = 0...

Varsha Sivaganesh 1A

I think Boltzmann's equation ignores thermal entropy altogether.

Varsha Sivaganesh 1A

Well in class, Lavelle mentioned that in any spontaneous process, there is an increase in entropy. However, I'm not sure if that means ALL spontaneous processes have a positive $\Delta S$

Varsha Sivaganesh 1A

For these questions, does anyone know if we have to convert kJ to J to calculate entropy so that its units are J/K? Or can we leave it as kJ/K?

Varsha Sivaganesh 1A

Usually, if it is reversible and isothermal then the problem will probably indicate that the temperature is constant. In an irreversible expansion, the external pressure is constant.

Varsha Sivaganesh 1A

K Stefanescu 2I wrote:Will we also be given all of the enthalpy values needed to solve a problem? Are there ANY enthalpy values we should memorize (besides which ones are zero)?

I don't think there's any we have to memorize!

Varsha Sivaganesh 1A

How do you calculate bond enthalpies (for example, like in 8.67)? I thought it was products - reactants but for part a it looks like it's reactants - products?

Varsha Sivaganesh 1A

Is it on the homework? I also don't remember him going over that in class, so I'm gonna guess that we probably don't need to know it!

Varsha Sivaganesh 1A

Dylan Mai 1D wrote:There are 3 methods we know of right now correct?

Yes! The first method is using Hess's method, the second is using bond enthalpies, and the third is using standard enthalpies of formation. So it just depends on what information the question gives you.

Varsha Sivaganesh 1A

Even if there are, I don't think you need to worry about them :)

Varsha Sivaganesh 1A

There is not a change in temperature because the heat that is added at the plateaus is being used to break apart bonds in order to turn the solid into a liquid, or a liquid into a vapor.

Varsha Sivaganesh 1A

It was because we were given the equilibrium concentration of the final product and the initial concentrations of the reactants. When doing an ice table, if you aren't given the initial concentration of the product, you assume it is 0. So for the problem that Dr. Lavelle did in class, the initial co...

Varsha Sivaganesh 1A

I think that we will be given the information necessary to answer the question. For example, if we have to calculate the pKa, then we will either be given the Ka or a way to calculate it. But I'm pretty sure there is no need to memorize pKa/pKb/Ka/Kb or any constants like those!

Varsha Sivaganesh 1A

Hello,
is percent deprotonation the same thing as percent ionization? One of the TAs referred to it as percent deprotonation and I've never heard of that before so I was just wondering if they are the same :) If not, what's the difference?

Varsha Sivaganesh 1A

The different bond angles are 120 degrees and 90 degrees. I believe he 90 degree angles are between the axial bond and the lone pair electrons.

Varsha Sivaganesh 1A

Would you just get the number in front from what row the atom is in the periodic table? For example, for 2sp3, the element is in the second row?

Varsha Sivaganesh 1A

So the only things that you would use for the ICE table are aqueous and gases?

Varsha Sivaganesh 1A

I think in lecture, Dr. Lavelle said that you would put the ligand names in alphabetical order (ex: ammine) but when writing the formulas, I don't think there is a specific order that is needed (ex: NH3)

Varsha Sivaganesh 1A

You could also think of it as smaller cations having higher polarizing power!

Varsha Sivaganesh 1A

However, when comparing radii, you would use the same trend whether its atomic, ionic, or covalent radii.

Varsha Sivaganesh 1A

No, you can draw that if you would like to, but a regular Lewis dot structure will suffice. :) As long as you can also identify the shape and bond angles, I think you're good

Varsha Sivaganesh 1A

Usually it has to do with the formal charge. Some atoms work better when they don't have an octet because it makes their formal charge closer to 0. For example, if boron is bonded to three fluorine atoms via single bonds, the formal charge of all of those atoms is 0. However, if you were to give bor...

Varsha Sivaganesh 1A

Unless they tell you whether it is an s, p, d, or f orbital, you would just say that there are 5 possible l values and l could be 0, 1, 2, 3, 4, or 5. But unless they give you the letter I don't think there is any way of knowing what l's value is.

Varsha Sivaganesh 1A

For the test we will only need to know how to do the electron configurations for period 1-4, so I wouldn't worry about Rhodium! And I believe Copper and Chromium are the only exceptions we need to know about, just keep in mind that they are not the only two exceptions in the entire periodic table :)

Varsha Sivaganesh 1A

So we just need to know that Schrodinger's equation is used to find n, l, and ml?? Or is that not what it's used for...?

Varsha Sivaganesh 1A

Also, when you need to use De Broglie the problem will give you mass and/or velocity, whereas if you were to use the other equation relating wavelength to frequency, they would give you the frequency of the photon.

Varsha Sivaganesh 1A

The question is: The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? To what region of the electromagnetic spectrum does this wavelength correspond (i.e. infrared, ultraviolet...

Varsha Sivaganesh 1A

The question is: B. If molybdenum is irradiated with 194 nm light, what is the maximum possible kinetic energy of the emitted electrons? So from part A, I got 7.22 x 10^-19 J as the threshold energy. For this question, I tried using the equation E = hv and then substituting v = c/wavelength and when...

Varsha Sivaganesh 1A

For 28, what would you plug in for m in the equation E = 1/2mv^2? I am struggling with this one as well.

Varsha Sivaganesh 1A

I think once we begin learning to name compounds this will make more sense. Typically, when you name compounds that contain a transition metal + a nonmetal, you must indicate the charge of the transition metal, since some have multiple charges. For example, Fe2O3 would be written as iron (III) oxide...

Varsha Sivaganesh 1A

The question is: To prepare a fertilizer solution, a orist dilutes 1.0 L of 0.20 m NH4NO3(aq) by adding 3.0 L of water. The orist then adds 100. mL of the diluted solution to each plant. How many moles of nitrogen atoms will each plant receive? Solve this exercise without using a calculator. So far,...

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