CHEMISTRY COMMUNITY

Justin Chu 1G

I'm pretty sure that questions on the final won't be that simple, but technically yes. If, let's say, step 1 matched exactly the given rate law, you would be done with the problem there as step 1 would be the RDS, aka slow step. The only reason he manipulated the rate law in the second step was beca...

Justin Chu 1G

The way you find the slow step is you have to be given an overall rxn and an experimentally determined rate law. Then, from the proposed rxn mechanism, you would have to test each step to see which one matches the given rate law and the one that does is your rate-determining step, aka the slow step.

Justin Chu 1G

For 15.61, is the equation used in the solutions manual a derivation of the Arrhenius equation, and if so, does anyone know how you would go about deriving it? Just wondering since I don't see it on the equations sheet. Thanks!

Justin Chu 1G

Generally, the units are in kJ/mol. If anything, though, I think you can leave the answer in just kJ but definitely not just mol.

Justin Chu 1G

So essentially a catalyst is a substance that speeds up the reaction rate but is not consumed through the reaction itself. It does this by lowering the activation energy required for the reaction to occur (lowering the "hill" on the graph), making it easier to proceed with the reaction. As...

Justin Chu 1G

For the homework problems, I noticed that in 15.27 (first-order reaction), you could simply calculate how many half lives have occurred and multiply the number by the half-life (ex: 1/8 of the original concentration would equal (1/2)^3 so you could multiply the half life by 3). However, I noticed th...

Justin Chu 1G

This is because standard cell potential is not a state function so you cannot just add the E together. Rather, you have to find the G and then add those together I believe.

Justin Chu 1G

Only if all the other reactants remain constant. Otherwise, you would be unable to tell which change in concentration is affecting the rate and how.

Justin Chu 1G

Such as in 15.3C and 15.5, I just wanted some clarification on what "unique" rate of a reaction means.

Justin Chu 1G

You get the right answer if you use the logQ equation instead of the lnQ equation but I have no idea why it would matter either way.

Justin Chu 1G

When would you know to use the lnQ or logQ equations when finding cell potential? For example, the problem 14.47, I used the equation for lnQ and got lnQ=15, but the answer says 10^6, which would only be possible if using the logQ equation.

Justin Chu 1G

Just by looking at the balanced overall reaction or half-reactions, how can you tell when to include an something like platinum in the cell diagram?

Justin Chu 1G

How come when using the equation E(cathode)-E(anode), you don't flip the sign of the reduction potential if you are reversing the equation?

Justin Chu 1G

If you use the acronyms OIL RIG (oxidation is losing (e-), reduction is gaining) and An Ox/Red Cat (anode=oxidation, cathode=reduction), you can easily figure out which molecules are gaining/losing electrons and pair them up with their appropriate electrode.

Justin Chu 1G

For transitional metals, as you stated, it depends on the oxidation numbers of the other atoms present in the molecule. For MnO4-, you know the O's will have 2- each for a total of 8-. Because the overall compound has a charge of -, you know the Mn has to be 7+ to make this true.

Justin Chu 1G

That is correct.

Justin Chu 1G

Yea when the reaction is at equilibrium, you can simply use the K that's given to you.

Justin Chu 1G

This is because the total change in entropy is the sum of the change in the entropies of the system and the surroundings.

Justin Chu 1G

But if it gets colder, doesn't it mean that it is losing heat?

Justin Chu 1G

If the system is at equilibrium, anything lost must be regained in another form to regain a state of equilibrium (ex: q and w).

Justin Chu 1G

Yes, when only deltaS is asked, it should be assumed to be the entropy change for the system only. Anything else would have to be specified.

Justin Chu 1G

You would just use the equation nRln(V2/V1) where n is 4.80 mol and V2 is 4.80L and V1 is 12.86L.

Justin Chu 1G

Work is positive when work is done by the system and negative when work is done on the system.

Justin Chu 1G

Is it simply just due to the difference of a reversible vs irreversible reaction?

Justin Chu 1G

Based on my understanding, a reversible reaction always does the max amount of work possible since it would have to be in equilibrium. Also, all real processes are irreversible and these irreversible reactions tend to be much faster but less efficient (do less work).

Justin Chu 1G

Conversely you could also multiply the first equation by 2 to get 4 NO + 2 O2 --> 4 NO2. In this case you would also have to multiply the deltaH by 2. Then the 4 NO2s would cancel out leaving you with the first equation being 4 NO + 2 O2 --> and the second equation with O2 --> 2 N2O5. You would then...

Justin Chu 1G

I think generally the R we use more often will contain the units L.atm/mol.K

Justin Chu 1G

I think it's because the entire equation (deltaH or q) uses the CHANGE in temperature and not the VALUE of the temperature so the change in degrees Celsius vs the change in degrees Kelvin would be the exact same change as Kelvin is simply Celsius + 273.

Justin Chu 1G

Making bad chemistry jokes because all the good ones Argon.

Justin Chu 1G

I asked the guy sitting next to me if he had any sodium hypobromite…
He said NaBrO

Justin Chu 1G

We are in the same discussion so do you want to just take a picture of my notes next discussion section?

Justin Chu 1G

It might also be a good idea to just remember some of the more common strong acids such as HCl, HBr, HI, HNO3, H2SO4, and HClO4.

Justin Chu 1G

Also, the diagonal strip of metalloids on the periodic table generally contain the elements that will form amphoteric compounds (however, NOT ALL).

Justin Chu 1G

Another instance of delocalization would be in a benzene ring where all the bonds are shared equally over the entire ring.

Justin Chu 1G

I don't think you have to indicate the charge on each individual ligand in a coordination compound, as it would be noted in the overall charge at the end regardless.

Justin Chu 1G

This is because for Kc, you already state which molecule you are referring to in brackets (i.e. [H20]) when referring to its concentration.

Justin Chu 1G

Is there a way to tell just by looking at the formula or name of a ligand to tell if it is polydentate (ex: en is bidentate) or would those just have to be memorized?

Justin Chu 1G

For elements with expanded octets, what is the maximum number of extra electrons it can hold?

Justin Chu 1G

For the Lewis structure for iodate, the solutions manual gives it to be central atom I with with 3 single bonds connected to the 3 O. Based off formal charge, wouldn't we rather have 3 double bonds to connect the 3 O and then just leave the FC on the central I to be -1?

Justin Chu 1G

In nature, I'm pretty sure that the real structure is a blend of all resonance structures so I don't think one would occur more frequently. However, the most stable structure (with the least formal charge) is the biggest contributor to the structure.

Justin Chu 1G

I think it is pure memorization for the bond angles of basic structures (ex: tetrahedral or trigonal planar). For the more advanced structures with lone pairs, I think you just have to know that the lone pairs will push the bonded atoms closer together and make the bond angle smaller than it was ori...

Justin Chu 1G

Resonance structures occur when there are multiple places where you could put a double/triple bond and all the possible variants would still be equal. The real structure would be a combination of all the resonance structures, therefore making a fractional bond length that is the average. The only re...

Justin Chu 1G

What gives ionic bonds partial covalent character and how does this make it different from simply an ionic bond?

Justin Chu 1G

When you remove an electron, can you always tell which electron is going to be removed just by looking at the last part of an electron configuration? For example, 1s2 2s2 2p5, would the electron being removed be from the 2p5 orbital?

Justin Chu 1G

For part A, when it asks for the ground-state electron configuration for Cu+, since you are losing 1 more electron, would the configuration be 3d8 4s2 or would it take both electrons to become 3d10?

Justin Chu 1G

That is correct. For the d-orbital, you can have 5 different numbers for your magnetic quantum number, specifically -2, -1, 0, 1, 2. Can someone please explain how you get the magnetic quantum numbers of -2, -1, 0, 1, 2? So basically for the magnetic quantum number, you can have values of l, -l, an...

Justin Chu 1G

That is correct. For the d-orbital, you can have 5 different numbers for your magnetic quantum number, specifically -2, -1, 0, 1, 2.

Justin Chu 1G

Based on just the information given, I think you would only be able to find the first two quantum numbers. You would need the full electron configuration to find more quantum numbers (ex: 1s2 2s2 2p5).

Justin Chu 1G

Normally I would just look at what information I am given to figure out what equation(s) I should use to solve my problem as, quite often, you can use many different methods to solve a problem. For the de Broglie equation, I think you would use it when given mass and speed of a particle to find its ...

Justin Chu 1G

If you know 1 Watt = 1 Joule per second, you can figure out that in 2 seconds, you generate 64 Joules of energy. With your wavelength, you can use it to find the frequency as you also know the speed of light constant. After, you can multiply the frequency with Planck's constant to find how much ener...

Justin Chu 1G

Although catalysts are not necessary to include in a chemical reaction, I think they are still often referenced by writing them above the arrow, no?

Justin Chu 1G

Generally, anything that doesn't seem like it can be easily multiplied into another whole number (ex: 1.5 x 2, 2.67 x 3) can be easily rounded to its nearest integer. This usually just happens due to rounding errors with sig figs so I wouldn't worry too much. They are almost always apparent what the...

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