CHEMISTRY COMMUNITY

Danny Zhang 4L

Catalysts appear as a reactant for the first step of the reaction mechanism, while intermediates are formed during the reaction. They are both left out of the overall equation of the reaction.

Danny Zhang 4L

To my understanding, the question could have just told us that "k = 0.015 L mol-1 min-1 for the rate law of this reaction", and that would not change how you should approach the problem.

Danny Zhang 4L

It will be 8 questions just like the midterm, but there will be more small parts to each of them.

Danny Zhang 4L

A large K suggests that the forward reaction is favored. This means that the products are relatively more stable compared to the reactants because the reactants will have a tendency to split/change.

Danny Zhang 4L

To my understanding, a large K tells us that the forward reaction is favored. This means that the reactants have a tendency to split and/or change, making them unstable. Therefore, the products are relatively stable when compared to the reactants.

Danny Zhang 4L

Because this class is cumulative, chem equilibrium will definely show up in a problem or two on the final

Danny Zhang 4L

You will need it in the absence of solid for either of the half reactions

Danny Zhang 4L

You will only need to include H+ and OH-.

Danny Zhang 4L

Going further with the directions that is provided, you can calculate ΔG^(o) with the K given to you through -RTln(K).

Danny Zhang 4L

When it's not given, it is usually suggested to be 298K.

Danny Zhang 4L

I believe that the reaction is at equilibrium if delta G is zero.

Danny Zhang 4L

^To add on to the previous comment, we only need to study electrochemistry material up to what we went over in lecture on Friday.

Danny Zhang 4L

Delta U=0 assumes an isothermal process because of delta U=(3/2)nR(delta T). When delta U is zero, delta T will have to be zero as well for the equation to be true.

Danny Zhang 4L

(# of mircostates)^(# of molecules)

Danny Zhang 4L

Last quarter, they gave it back in lectures 1 week after we took the midterm.

Danny Zhang 4L

In my opinion, the best way to prepare is doing the practice midterms that are given out during review sessions.

Danny Zhang 4L

Cv is the heat capacity of the system when the volume is constant.

Danny Zhang 4L

The topics tested on the midterm should cover everything about entropy up until the introduction of Gibbs free energy. According to the textbook, the last topic for midterm is the entropy of surroundings.

Danny Zhang 4L

J is what is most commonly used to represent work. We can of course use kJ to represent work as well when specified by the problem.

Danny Zhang 4L

U represents the internal energy of a system. Its relation to work can be seen in the first law of thermodynamics: change in U = q(heat exchanged) + w(work done on or by the system).

Danny Zhang 4L

I believe that the main things to consider about work in thermodynamics are that negative work is done onto the system(compression of gas) and that positive work is done by the system(expansion of gas).

Danny Zhang 4L

pH tells us how acidic or basic something is. We can find pH through -log([H+]). We can also find pH if we only have pOH(log([OH-])) using the relationship pH+pOH=14.

Danny Zhang 4L

Because H2SO4 is a strong acid, it will not have a Ka value because it completely dissociates into H and HSO4 when it first loses the hydrogen.

Danny Zhang 4L

You can really only use kc in place of kp when all of the compounds involved in the reaction are in the gaseous phase.

Danny Zhang 4L

I don't believe I have ever seen Ka and Kb sharing an inverse relationship from the doing the textbook problems. I believe the only relevant relationship is Ka x Kb = Kw.

Danny Zhang 4L

K will not change if the concentrations of both the reactants and the products change by the same amount. This is the case because their ratio would remain the same.

Danny Zhang 4L

Yes, the concentration of hydronium and hydroxide are equal in pure(neutral) water.

Danny Zhang 4L

K is the equilibrium constant. It represents the ratio of the concentration of products to the concentration of reactants in a reaction that tells us when the rate of forward reaction and the rate of reverse reaction are equal.

Danny Zhang 4L

When Q is smaller than K, it suggests that there is greater concentration of reactants and less concentration of products than suggested at equilibrium. Therefore, the reaction will take a forward direction to lower the concentration of reactants and increase the concentration of products until Q=K.

Danny Zhang 4L

The formulas for both Q and K are the same. K specifically tells us when the reaction is at equilibrium. Q can be be found during any instance of the reaction in order to determine which direction the reaction is going when it is compared to K.

Danny Zhang 4L

There is no dipole-dipole interaction as the net dipole moment is zero.

Danny Zhang 4L

The only things that affect the shape of a molecule are the central atom's lone pairs and the bonds it formed.

Danny Zhang 4L

There will always be a slight difference because of the unique properties of molecules that affect their interactions.

Danny Zhang 4L

The VESPR formula AX2E2 suggests that the shape of the molecule is bent/angular, which means that the bond angles are less than 109.5 degrees.

Danny Zhang 4L

Just as you mentioned, NO2 is polar because of the bent shape of the atoms as it prevents the dipole moments from canceling out.

Danny Zhang 4L

I would always like to look at dipole moments as vectors. Looking at option 1, adding the two vectors (dipole moments) together gives us a resultant vector with a larger magnitude than the resultant vector for option 2.

Danny Zhang 4L

We treat double bonds and triple bonds like they are a single bond with one region of electron density in the VESPR model.

Danny Zhang 4L

Either way is fine. It's just whether or not you prefer using sp^3d to follow the order of increasing energy of orbitals as we did for electron configurations.

Danny Zhang 4L

I believe just putting "less than 109.5 degrees" is fine for all bond angles around 100-109 degrees.

Danny Zhang 4L

We just have to turn in 14 homework problems during week 9 to make up for missing week 8 discussion section.

Danny Zhang 4L

I believe the main difference to know is that London forces occur in all molecules while dipole-dipole forces only occur in polar molecules.

Danny Zhang 4L

It starts right after Thanksgiving break, which is great because more time to study!

Danny Zhang 4L

Given that the energy is found through -(hR/n^2), increasing n would indicate greater energy as the result becomes less negative. If we use hR/n^2 to find the energy instead, increasing n would result in lower energy values, which is not correct.

Danny Zhang 4L

For all of the Lewis structure questions I've done so far, I have only aimed for 0 formal charges for the most stable structure. If it was a polyatomic/monatomic ion, then I aim for one atom having the indicated charge.

Danny Zhang 4L

Our calculations will only give us the theoretical yields. The actual yield will always be given to us according to experimental results.

Danny Zhang 4L

Greater electronegativity is the same as saying greater attraction of other electrons.

Danny Zhang 4L

They are both correct. However, professor Lavelle prefers using negative signs to clearly indicate that higher n results in higher energy.

Danny Zhang 4L

We use the negative sign to clearly indicate that energy increases as n increases.

Danny Zhang 4L

For Bi and Si, you are finding the odd number of electrons in the p orbitals. However, for Ta and Ni, you are finding the odd number of electrons in the d orbitals

Danny Zhang 4L

Within this class, I believe that we will only be using kg when dealing with energy and momentum.

Danny Zhang 4L

For hydrogen, all orbitals share the same energy, so the degeneracy of an orbital simply depends on how many exist. For multi-electron atoms, only orbitals that share the same l quantum number have the same energy, so the degeneracy of an orbital would then depend on how many possible orbitals is po...

Danny Zhang 4L

Because of the inverse relationship between momentum and wavelength shown in the de Broglie equation(λ=h/p), increasing the uncertainty of momentum will decrease the uncertainty of wavelength.

Danny Zhang 4L

Because of the inverse relationship between momentum and wavelength shown in the de Broglie equation(λ=h/p), increasing the uncertainty of momentum will decrease the uncertainty of wavelength.

Danny Zhang 4L

I believe that it will be important to know the order of the regions of the electromagnetic spectrum, as I feel that questions on ordering waves based on frequency, wavelength, or energy will pop up on the test

Danny Zhang 4L

I believe that we will not see our grades until the end of the quarter, at least that is what is suggested by our syllabus. We can only keep track of our scores ourselves with the tests and homework being passed back.

Danny Zhang 4L

Both wavelength and frequency play a part in determining the color of light. It's just that visible spectrum diagrams always use wavelength to indicate the color.

Danny Zhang 4L

Anjali 4A wrote:Will we be provided all of these constants/equations during the tests, midterms and final?

I am sure that we will get a cover sheet with all of the constants/equations as we did on the first test on all future tests as well.

Danny Zhang 4L

By next week, are you referring to 10/15 through 10/19 or 10/22 through 10/26?

Danny Zhang 4L

Tamera Scott 3L wrote:I've also seen E=hf once, does anyone know if that is the same as E=hv?

I believe that f and v both symbolize frequency. I think that v is just more commonly used in chemistry while f is more preferred in physics.

Danny Zhang 4L

Question: (a) Write the formula for nitric acid. (b) Without doing a calculation, estimate which element in nitric acid occurs with the greatest mass percentage. I am only using this problem as an example. When the question asks for the formula of a certain compound, are we supposed to figure it out...

Danny Zhang 4L

Considering what Dr.Lavelle said in class on Monday, I believe that it is fine for the answers' units to be in any form for problems in homework and tests when it is not specified. He mentioned that we may want our units to be simplified a certain way only if we are in a lab setting.

Danny Zhang 4L

Question: The field of nanotechnology offers some intriguing possibilities, such as the creation of fibers one atom wide. Suppose you were able to string together 1.00 mol Ag atoms, each of radius 144 pm, into one of these fibers by encapsulating them in carbon nanotubes (see Chapter 6). How long wo...

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