CHEMISTRY COMMUNITY

bonnie_schmitz_1F

When using Nerst equation, do we have to worry about the units of Farraday's constant being in Coulombs while R is in joules?

bonnie_schmitz_1F

In problem 6L.3 c), there are two moles of Ce4+ + 1e- --> Ce3+ however the E˚ value does not change. Do E˚ values ever change with the number of moles increases?

bonnie_schmitz_1F

004932366 wrote:At constant pressure with no nonexpansion work, delta H is equal to q.

So at constant pressure and constant volume?

bonnie_schmitz_1F

When is the standard gibbs free energy of formation equal to zero?

bonnie_schmitz_1F

k' is generally used instead of k to symbolize the rate of the reverse reaction, as to your specific question, A is probably in the products of the reaction you are looking at, which is why you would have k'. However, you would need to see the reaction to know this for sure. Do you have the given r...

bonnie_schmitz_1F

Under what conditions does ∆H equal q?

bonnie_schmitz_1F

In problem 10, how do we know that ∆H = q?

bonnie_schmitz_1F

I'm still a little confused on this concept on determining the rate. In lecture, we said if [A]0 >> [B]0 and [C]0 then rate = k'[A]^N. Why do we use k' instead of k?

bonnie_schmitz_1F

I have a picture from afar of Michelle receiving her award!

bonnie_schmitz_1F

Yvonne Du wrote:A catalyst is involved in the starting of the reaction, while an intermediate joins in later. Both of them are not included in the rate law.

Today, my TA said that a catalyst can be included in the rate law. Can someone clarify?

bonnie_schmitz_1F

What are some good keywords to search to find review sheets from the TAs and UAs?

bonnie_schmitz_1F

In the review session tonight, the TA used the word adiabatic to describe a reaction in which we knew q=0 because it was "adiabatic." Does adiabatic mean the same thing as isothermic?

bonnie_schmitz_1F

An intermediate is something formed in a reaction and then used up later. A catalyst is present at the beginning of the reaction.

bonnie_schmitz_1F

Thank you!

bonnie_schmitz_1F

Thank you!

bonnie_schmitz_1F

What factors affect k? Does it change with temperature like equilibrium constants? Is k different for every reaction?

bonnie_schmitz_1F

I'm not sure the answer to this question exactly, but I think we should know the graphs for different order reaction. For a first order reaction, there is a linear plot of ln[A] vs. t For a second order reaction, there is a linear plot of 1/[A] vs. t For a zero order reaction, there is a linear plot...

bonnie_schmitz_1F

How do we know if a reaction is first/second order? and What does it mean for a reaction to be first/second order?

bonnie_schmitz_1F

I think you would need to find both and then from there you can tell which direction the reaction is preceding based on Q's relationship to K.

bonnie_schmitz_1F

I was absent from class on Wednesday and Thursday of last week because I was away at a swim meet. Can someone tell me what we covered in class?

bonnie_schmitz_1F

As the temperature increases and the change in enthalpy and the change in entropy stay constant, the change in gibbs free energy decreases and vice versa. This can be seen in the equation ∆G = ∆H - T∆S.

bonnie_schmitz_1F

So will we need all of enthalpy and entropy for test 2?

bonnie_schmitz_1F

I agree, I don't think we will have to know how to derive the equations, but we will need to know how/when to use and apply them. Additionally, I think understanding the derivations helps make the material clearer and gives a deeper understand of why that equations works.

bonnie_schmitz_1F

The main role of a salt bridge is to maintain neutrality in the cathode and the anode so the flow of electrons is continuous.

bonnie_schmitz_1F

To add to what Eunice Lee 1A said, I think that the Pt is written on whichever side (either anode, cathode, or both) do not have a solid substance (so both are aqueous solutions)

bonnie_schmitz_1F

I think it all comes back to this equation: ∆G = ∆H - T∆S

bonnie_schmitz_1F

904936893 wrote:If K = 0, is the reaction at equilibrium?

I think so since the reaction is no longer releasing or requiring energy.

bonnie_schmitz_1F

Spontaneous means the reaction is happening on its own, meaning there is no extra energy input require. Exergonic reactions are spontaneous since they happened without the addition of energy.

bonnie_schmitz_1F

Can anyone explain 3b?

bonnie_schmitz_1F

Why in finding the heat capacity of the calorimeter do we ignore n in the equation q = nC∆T? I think it has something to do with heat capacity vs. specific heat but I'm not sure.

bonnie_schmitz_1F

In this problem, the solutions manual says that heat lost by metal = - heat gained by water. Why would the heat gained by water be negative?

bonnie_schmitz_1F

I'm assuming the same ones since they are during the different lecture times, but I'm not sure.

bonnie_schmitz_1F

Will we ever need to use the integral equation or do we just need to understand it and be able to apply the variations of it?

bonnie_schmitz_1F

In class we said that ∆S = KB ln (v2/v1) and that ∆S = nR ln (v2/v1). In this case, Boltzmann's constant and R times the number of moles must be equal. However, the number of moles can change for different gases, so can someone explain why these equations are equal?

bonnie_schmitz_1F

In class today, Professor Lavelle said that doubling the volume of an ideal gas also doubles w, the amount of degenerate states, because each gas molecule has 2x the positions availible to it. I'm still confused what the relationship between volume and degenerate states are. Why does doubling the vo...

bonnie_schmitz_1F

Why is a system is at equilibrium is the internal pressure approximately equal to the external pressure?

bonnie_schmitz_1F

Im still a little confused on the definition of enthalpy, specifically in relationship to heat. So how is enthalpy different than heat?

bonnie_schmitz_1F

I think because there is no carbon on the reactants side of the equation. So it would just be 2 H2 + O2 --> 2 H20

bonnie_schmitz_1F

Hess's method is where you look at multiple different reactions and their standard reaction enthalpies to determine the standard reaction enthalpy of you desired reaction. This is an example from class: We want the standard enthalpy for N2 + 2 O2 --> 2 NO2 N2 + O2 --> 2 NO ∆H = 180 kJ 2 NO + 02 --> ...

bonnie_schmitz_1F

Are the lecture slides posted anywhere online?

bonnie_schmitz_1F

What are the units for enthalpy? Sometimes its written in kJ but other times its kJ mol-1. Is there a difference?

bonnie_schmitz_1F

I'm not sure there is a specific case when you need to use one or the other, I think it depends more on what the problems gives you.

bonnie_schmitz_1F

The autoprotolysis constant is Kw = [H3O+][OH-] = 1.0 x 10^-14 where the concentration of H3O+ and OH- are 1.0 x 10^-7

bonnie_schmitz_1F

In class we were given a problem that said: What is the pH of a solution with 0.100 M HNO2 and 0.150 M KNO2? The equation we used was to describe this reaction was HNO2 + H2O --> H3O+ + NO2- I understand that K + is not included in the equation because it is on both sides, however, why wouldn't ther...

bonnie_schmitz_1F

Yes, bar is a unit to measure pressure which is approximately equal to an atm, however its slightly larger.

bonnie_schmitz_1F

For 5G.11a, the different components are in different states of matter, so I'm not sure how to calculate Q. Can someone explain how I would do this?

bonnie_schmitz_1F

In general how can you tell if determine if a reaction is exothermic or endothermic?

bonnie_schmitz_1F

I'm confused why KF would form a solution with a pH greater than 7 but then KBr's solution is still neutral.

bonnie_schmitz_1F

The number inside the parentheses is the new molarity that they found using the eqautions: (M_initialV_initial)/V_final = M_final.

bonnie_schmitz_1F

I don't understand how to calculate which is the stronger base. Can someone explain it?

bonnie_schmitz_1F

Is iron always at the center of a heme complex?

bonnie_schmitz_1F

I think I understand the basis of how to do number 34, but I keep getting a pH of 2.10. Did anyone else make the error same/know what my error is?

bonnie_schmitz_1F

For question 18, I'm having trouble finding the 180˚ bond. Which bond would it be?

bonnie_schmitz_1F

Yes thank you! Sorry I was reading part of 2D.19 then I looked at 2D.20 to get the part about the nitrogens!

bonnie_schmitz_1F

I'm very confused on this problem! I thought I just added the covalent radii of the nitrogen atoms but the solutions manual says something else. Can anyone help me understand how to solve a problem like this?

bonnie_schmitz_1F

In class today, we saw how the nickel in [Ni (NH3)4 Cl] Cl 2 H2O had a charge of positive 2. I understand that the charge of +2 comes from the -1 charge on both of the Chlorine atoms, but how does the chlorine outside of the coordination compound affect the charge of the TM? Are the compounds outsid...

bonnie_schmitz_1F

A lewis acid is the electron acceptor and the lewis base is the electron donor!

bonnie_schmitz_1F

How do double bonds affect hybridization?

bonnie_schmitz_1F

Electron arrangement is the arrangement of electrons around the central atoms. So for example if an atom has two bonded pairs and two lone pair electrons, the electron geometry is tetrahedral. The molecular geometry is arrangement of the atoms around the central atom. While this does take into accou...

bonnie_schmitz_1F

Angular shape is when there is a central atom with two bonded molecules and one lone pair.

bonnie_schmitz_1F

Additionally, ionic bonds are intramolecular while hydrogen bonds are intermolecular. And intramolecular bonds are always stronger than hydrogen bonds.

bonnie_schmitz_1F

You need to look at whether the electrons clouds are bonded electrons or lone pair electrons. When determining a molecule's VSEPR structure you look at bonded molecules, but also need to take into account where the lone pair electrons, if there are any, are located. As for your question, below are t...

bonnie_schmitz_1F

I think radicals are more reactive because they have an unequal number of electrons to match the number of protons in addition to the one electron not in a pair. Additionally, halogens are diatomic elements which means that they are usually found in pairs to eliminate the one unpaired electron.

bonnie_schmitz_1F

I believe that the Lewis structure for NO2 has one single bond and one double bond. So, in nature, this double bond would be evenly distributed between the two, so I assumed the each bond would be approximately a "1.5" bond. Using this logic, I guessed that the bond length would be about 1...

bonnie_schmitz_1F

SO2 can't form hydrogen bonds because there is no hydrogen. The bonds are polar as the S is slightly positive and the O is slightly negative, so there is some intermolecular bonding happening there, but without hydrogen, they are not classified as hydrogen bonds.

bonnie_schmitz_1F

Well in a lot of cases not all of the atoms can have a formal charge of zero. In Lewis structures, I think we want as many atoms to have a formal charge of 0 as possible, but its especially important that the central atom have a formal charge of 0. Additionally there are only a few atoms that can ha...

bonnie_schmitz_1F

In my discussion, we saw how Be has a larger ionization energy than B even though B is farther to the right than Be because B has 1 electron in the 2p-orbital while Be has a full 2s-orbital. The same was true for N having a larger ionization energy than O because of its half full 2p-orbital. How do ...

bonnie_schmitz_1F

I don't think so either since they were not covered in the classes that he said the midterm would cover

bonnie_schmitz_1F

The Na+ atom would be smaller and the Ne atom would bigger because they have the same number of electrons. However, since Na+ has one more proton, it has a tighter hold on its 10 electrons which makes the atom smaller.

bonnie_schmitz_1F

Based on what we've seen in class, I'm assuming the first electron in an orbital spins upwards (+1/2) and the second electron spins downwards (-1/2). Is this right?

bonnie_schmitz_1F

As I was going through this problem, I realized once I got to the fourth energy level, I was unsure when to add 4f. For example, Sb goes from 4d10 to 5s2, but then W goes 4f14, 5d4, 6s2. Could someone explain when you should include the f orbital?

bonnie_schmitz_1F

In the M number, does -1 always correspond to x? For example is wave function (2,1, -1) have to mean 2px? or could it be 2py?

bonnie_schmitz_1F

I'm a little confused about the idea of electron spin. Why do electrons spin and why is the quantum number associated with it +/- 1/2?

bonnie_schmitz_1F

In high school, I remember learning that the 4s- shell was before the 3d- shell because of how much larger the 3d- one was. Is this right?

bonnie_schmitz_1F

Short wavelengths can eject the electron because as Johnathan said they have a higher energy. The energy equation is E = hv. H is planck's constant, so that value never changes. However, the v is in regards to frequency, and we know that wavelength and frequency are inversely proportional (c = λ * v...

bonnie_schmitz_1F

I would say that you don't need to memorize the all of different wavelengths, but I would know the order of the different wavelengths and have a general idea of the range of wavelengths for each type if light.

bonnie_schmitz_1F

I got the same answer as you and was also unsure how to get the correct answer here. Something I was wondering about was the units of the reactants: one was 0.750 g of C6H9Cl3 which is grams and the other, 1.000 kg of AgNO3, is in kilograms. I thought there might be a typo and they both should have ...

bonnie_schmitz_1F

I'm not sure if this is correct, but my understanding is this:

atom: 1 unit of one element. for example, H is 1 hydrogen atom.
molecule: a molecule is a 2 or more atoms bonded together.
formula unit: the empirical formula of a compound.

bonnie_schmitz_1F

In response to @Kristen Kim 1I question about the online discussion, I asked my TA and she said that we ask a question/comment three times per week to earn the 3 points!

bonnie_schmitz_1F

In this case, I'm not sure its completely necessary to find the percent composition because the question you're referring did not ask for it. Using the percent composition is definitely one way to do the problem, but you could do it another way since you know the mass of both substances. Here is my ...

bonnie_schmitz_1F

How are you all picking which problems to do? I was thinking of turning in about one from the various fundamentals sections, but I was wondering if anyone had any other suggestions on which problems to do/turn in!

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