CHEMISTRY COMMUNITY

Sue Xu 2K

For the cell diagram that Dr. Lavelle covers in his review session, Ag(s)|AgBr(s)||Br-(aq)|Br2(g)|Pt(s), do we need a line between Ag(s) and AgBr(s)?

Sue Xu 2K

In the answer key of 15.85, what does it mean by the dots in the structures of the activated complex? Also, is the activated complex equal to the intermediate?

Sue Xu 2K

Which part of the reaction profile indicates the intermediates?

Sue Xu 2K

What is different if the reaction takes place in organic solvent?

Sue Xu 2K

It is possible to solve the question without the volume, but you can still calculate the concentration with the mass and the volume first and then calculate the final mass.

Sue Xu 2K

There several ways to solve rate constant: the differential rate law (rate = k[R]^n ) and the integral rate law (vary depending on the order of the reaction). For both of them you would probably need something more than the order and the initial concentration.

Sue Xu 2K

Are there reactions with a order less than 0? For example, the rate law = k [R]^-1

Sue Xu 2K

There are multiple ways of calculating k. If we have the initial concentrations and rates, we can use the differential rate law, rate = k [A]^n to calculate k, in which n is the order of the reaction, and [A] is the initial concentration of the reactants.

Sue Xu 2K

I have the same question. I think the answer key is wrong. It should either be 2.85 x 10-^12 mol/Ls or 2.85 mmol/Ls.

Sue Xu 2K

For this question, I think we should divide the initial rate by 3 when calculating k, since it's the initial rate of G. But the answer key gives the value that are calculated without dividing by 3. Could anyone explain this?

Sue Xu 2K

Our TA told us to list the reactants first and then products.

Sue Xu 2K

You can find this on the class website: https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf
it says the solution manual is wrong.

Sue Xu 2K

For HW 14.117 it asks for the current. Could someone remind me the equation for current?

Sue Xu 2K

When we write cell diagrams, is there an rule for the order of substances in the same phase? Like Zn2+(aq), H+(aq)

Sue Xu 2K

Just want to make sure are we not going to have class on Wednesday because of the midterm?

Sue Xu 2K

I think he said we don't have to be too specific about the difference between kJ/mol and kJ. For the test and examples we cover in class we usually just use kJ.

Sue Xu 2K

I believe you are asking for question 9.75. For the trans molecules the two X (blue) atoms are on the opposite position. Given that the molecule is octahedral, there will be 3 microstates. And for the cis molecule there are 8 microstates.

Sue Xu 2K

What you are thinking is right but I think the question asks for the stability of the compounds instead of the elements. If the formation energy is positive, the compound form has more energy and is thus more unstable.

Sue Xu 2K

Is Van‘t Hoff equation going to be given during the test? I ask this because I could not find it on the constants and formulas page on test 1.

Sue Xu 2K

It is a minor thing but I just wonder that do we always have to put a + mark before positive cell potentials? 　

Sue Xu 2K

Do we have to put comma between substances of the same phases? Like H+(aq), OH-(aq).

Sue Xu 2K

The question asks the redox potential of U^(4+) + 4e- = U(s). How to approach this question? I tried to add the redox potential for U^(3+) + 3e = U(s) and
U^(4+) + e- = U^(3+) but I got -2.4V instead of -1.5V in the answer keys.

Sue Xu 2K

You can just generally look at the phase of the phase of the reactants and products. In this reaction, the reactants are 1 solid and 1 gas, while the products are 1 liquid and 1 gas. Because liquid has higher entropy than solid, the entropy of the products is higher.

Sue Xu 2K

I have the same question. Just replying to mark this.

Sue Xu 2K

Is the term "free expansion" the same as irreversible expansion?

Sue Xu 2K

In 9.7 I believe we have to use the equation S = nCp lnT1/T2. Are we always given the value of Cp?

Sue Xu 2K

For reversible expansion, it is isothermal because the system does work and lose energy, and then the loss of energy is replaced by the heat flow into the system. So U, the internal energy, remains constant. For U = 3/2 nRT, T also stays constant.

Sue Xu 2K

The way works for me is to simply think that reversible expansion is a slow, equilibrium process, and the changes of pressure happen in a lot of small steps. For the irreversible expansion, the pressure changes in one step and stays there for the rest of the process.

Sue Xu 2K

What is the unit of P, pressure in the w=-P delta V ? And is Torr the same as Pa?

Sue Xu 2K

The answer for this question is 25C, but shouldn't that be 24.7 with 3 sig figs?

Sue Xu 2K

Why is it w=-PV instead of w=PV? What does the minus mean?

Sue Xu 2K

We talked about delta U in class. Could some one please explain to me again what exactly it is?

Sue Xu 2K

Condensation, solidification and deposition are all exothermic phase change that release heat during the process.

Sue Xu 2K

I believe the unite for heat capacity should be kJ/C

Sue Xu 2K

The steam and water all tend to cool down when it get exposed to a cooler surface like the skin. But it releases extra energy to convert steam to water first, and then the extra energy, or extra heat would burns the skin worse.

Sue Xu 2K

I believe there is only lecture outlines on the class websites that list some central concepts and skills.

Sue Xu 2K

Just want to make sure, we can hand in the homework for week 1 in the next week's discussion session right?

Sue Xu 2K

Are we supposed to know the full name of these two ligands?

Sue Xu 2K

Can ligands be positively charged？

Sue Xu 2K

Can anyone please explain how the delocalized π bonds in Benzene work?

Sue Xu 2K

According to the answer, CO3 2- can be mono- or bidentate. How can it be either way? In my understanding, it is bidentate because two oxygen atoms can bind to a central metal.

Sue Xu 2K

Do we have to memorize all the prefix and names in the tests? Or are we getting the tables in the text book?

Sue Xu 2K

It asks for the formula of pentaamminesulfatocobalt(III) chloride. Is the answer wrong? I think it's [Co(NH3)5(SO4)]Cl3 since it said the (III).

Sue Xu 2K

I think lone pairs won't directly change the dipole moment, but they do change the shape of the molecule, like the lone pair in NH3 which makes it a trigonal pyramidal shape instead of trigonal planar. And the shape of the molecule will in turn influence the dipole moment.

Sue Xu 2K

Why is the statement "higher frequency light always emits electrons with higher kinetic energies" incorrect?

Sue Xu 2K

What exactly is formula unit？

Sue Xu 2K

I think it is mentioned in class, but I am a little bit confused about it. Is there one double S=O bond which forms a resonance structure?

Sue Xu 2K

How many valence electrons are there in elements like Cu and Br? Or specifically, does the electrons in d orbital count? The d orbital is from the inner shells so I'm not really sure.

Sue Xu 2K

In homework question 2.43 the configuration of tungsten, there are 4 electrons fill in 5d and 2 electrons in 6s. Why is the electrons not acting as they do in chromium, making the d-orbital half-filled?

Sue Xu 2K

In the homework question 2.37 it says "an electron in an s-orbital can penetrate to the nucleus of the atom". What does it mean by "penetrate"?

Sue Xu 2K

The orbitals are always the most stable when they are half filled or full, because of the electron repulsion force. So the electron will alway try to fill in the orbitals that way.

Sue Xu 2K

Since the electrons fill the 4s orbital first, can we say that the 4s orbital is in lower energy than the 3d orbital?

Sue Xu 2K

Bohr condition states that only if the energy of the photon mathces the difference of the electron energy shells that the photon can be emitted or observed. And Rydberg constant is basically how you can calculate the difference. These two togetherrr can solve the atomic spectrum problems.

Sue Xu 2K

When deriving the DeBroglie equation we need the equation E=pv. Where do we get this equation?
Also, if p=mv then E=mv^2. What does this have to do with the Kinetic energy Ek=(1/2)mv^2?

Sue Xu 2K

I think it would be from the wave mode to the photon or particle mode. Not sure which word is correct. Basically the experimental observations of photoelectric experiments is that no electrons are ejected unless the radiation has a frequency above a certain threshold value that is characteristic of ...

Sue Xu 2K

It is said that we get 1 point per post on this forum and there are 2 points at max each week. I wonder what is the last day of a "week", Friday or Sunday?

Sue Xu 2K

They both apply to every questions correctly. But the latter might involve more calculation.

Sue Xu 2K

Actually 1800 has 4 significant figures. the zeros count to the sig fig.

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