CHEMISTRY COMMUNITY

Alexandra Albers 1D

If you only added it to balance your half reactions, I'm not sure you need it to create your cell diagram. I am not totally sure, but I think you can just create your cell diagram with the substances that are being directly oxidized and reduced.

Alexandra Albers 1D

Maybe something about chlorofluorocarbons and the ozone layer, or examples of biological catalysts that, such as the examples in the book about poisons.

Alexandra Albers 1D

If we are finding a change in internal energy, it is likely we'll be given some indicator as to how heat is moving in and out of the system. I'm not sure we would be given temperatures, but heat changes are probably to be expected.

Alexandra Albers 1D

Even though half-life only determines the time required for a substance to decay to half of its original amount, in a half-life problem we may be asked to determine the time for a substance to decay to any amount. We should be able to manipulate the equation for half-life in order to find these valu...

Alexandra Albers 1D

So does the energy of the sun act like a catalyst? Or is it just providing heat to the reaction?

Alexandra Albers 1D

Dr. Lavelle may also adjust the grades after the final has been graded. In 14A, I believe his policy was that once all of the class averages were in, he would adjust the grading scale accordingly if it was needed. He will probably have a similar policy for 14B, though I wouldn't rely on this changin...

Alexandra Albers 1D

Dr. Lavelle may average the overall class grades based on the everyone's grades after the quarter is over, but I don't believe that this test in particular will have its scoring adjusted.

Alexandra Albers 1D

Delta G represents the change in Gibbs Free Energy of a reaction, but if there is a knot symbol, then you are working with standard Gibbs Free Energy.

Alexandra Albers 1D

T will only ever be given to you in Celsius or Kelvin, but for any calculations, you will almost certainly need to convert C to K in order to get the correct answer.

Alexandra Albers 1D

Electrons should be balanced after all elements have been balanced. The number of electrons in each half-reaction should be equal, so if they are not equal, multiply the equations by a coefficient to make them so.

Alexandra Albers 1D

An inert conductor which was mentioned in lecture and the textbook in particular was platinum, which is used in the redox reaction for hydrogen.

Alexandra Albers 1D

As far as the textbook goes, for the 7th edition does that mean that sections 6N and 6O will not be on the test? Will only the electrochemistry stuff up to 6M be included?

Alexandra Albers 1D

Does anyone know how much will be covered on Test 2? Is it only going to be Gibbs Free Energy stuff or will we cover electrochemistry as well?

Alexandra Albers 1D

In an isothermal reaction, delta U will be 0. Since this is the case, you will also know that q=-w or w=-q, so you can easily calculate one if you know the other.

Alexandra Albers 1D

They should be done in about a week or so, and if they're not, Dr. Lavelle will probably let us know that they're going to take longer.

Alexandra Albers 1D

The midterm will cover the entirety of outlines 1-3, I believe, but it will only cover most of outline 4. The last parts of outline 4 are about Gibbs Free Energy, which I don't think we need to know.

Alexandra Albers 1D

If a system is doing work on its surroundings (such as expanding volume against a piston), then work should be considered negative. If a system is having work done on it, then work is positive for the equation of internal energy (delta U).

Alexandra Albers 1D

In lecture, Dr. Lavelle indicated that from Gibbs Free Energy onward would not be included in the midterm. For the 7th edition, I believe that is the reading of sections 4J and the parts of 5G.

Alexandra Albers 1D

Nothing in an isolated system is exchanged with its surroundings, including heat or work. Right now, I don't think that we will have many problems involving calculations with isolated systems, if we have any.

Alexandra Albers 1D

So far, we have largely used atm for pressure measurements and have occasionally seen bar as well. From what I've seen, the units are only important for figuring out which version of the gas constant (R) we should use in calculations.

Alexandra Albers 1D

In some cases, such as that of delta U, particularly in biological reactions, qp and delta H can be equal because the there is not work due to expansion, meaning that delta U=delta H.

Alexandra Albers 1D

I believe that the way to solve this is that you add together the delta H of the first reaction (-1300 kJ) with the reversed delta H of the second reaction (+1560 kJ) because your original reaction involves the creation of C2H6 and not its breakdown. You have to therefore reverse the reaction and al...

Alexandra Albers 1D

atm and bar are both units of measurements for the partial pressures of gases. If you have a problem where you need to find the equilibrium constant in partial pressures then you can leave the gases in either atm or bar (whichever they are given in). The only time that the difference becomes relevan...

Alexandra Albers 1D

The modules he posted will likely be the only ones available for this quarter, but they are good review for the midterm and final as well and I would recommend doing them as practice for those.

Alexandra Albers 1D

Do we have to know anything about Gibbs Free Energy or the equations/diagrams related to it for this test? Or is that just stuff we should skip for now?

Alexandra Albers 1D

Also, if you are doing a problem where you have, for example: K=x^2/(0.2-x) and K is less than 10^-3, (0.2-x) can be approximated to just (0.2) but the x^2 should stay x^2 I believe.

Alexandra Albers 1D

No, everything up to Friday's lecture has to do with Test 1. What we go over on Monday will start the material for the next test.

Alexandra Albers 1D

R is the gas constant, which will most likely be given to us. T is the temperature, which will usually be given to us in either Celsius or Kelvin. If it is in Celsius, we will need to convert it to Kelvin by adding approximately 273 to the temperature in Celsius.

Alexandra Albers 1D

Kc is the equilibrium constant when using molar concentrations in the calculation and Kp is the equilibrium constant when using partial pressures. If your calculations use gases then either Kp or Kc, but if aqueous compounds are involved, only Kc would be used as only gases can have partial pressures.

Alexandra Albers 1D

Pure solids and liquids are ignored in finding K because they do not have an effect on the amount of reactant at equilibrium and they are kept at a value of 1 for the calculation.

Alexandra Albers 1D

First, use the equation Kinetic Energy=1/2*m*v^2 to figure out what v is. Then you need to use De Broglie's equation, so your wavelength is equal to Planck's constant over momentum (mass*velocity). If you plug in h, m, and v, you should be able to calculate your wavelength value.

Alexandra Albers 1D

I believe that when you have 5 regions of electron density, you always want to replace the equatorial areas with lone pairs before the axial. For Ax4E, you would replace the equatorial to get a seesaw, for AX3E2 you would replace the equatorial for T-shape, and for AX2E3, you would replace all equat...

Alexandra Albers 1D

I think we should probably know the list of neutral and anionic ligands that are on Dr. Lavelle's website as well as the naming rules from the textbook. I'm not sure how much they will come up on the final, but it is probably best to know them anyway.

Alexandra Albers 1D

In class, I believe Dr. Lavelle said that they truly only come very close to complete ionization, but for the purposes of this course we will say that they are ionized 100%.

Alexandra Albers 1D

Dr. Lavelle said that he wouldn't make us draw the VSEPR model, so it probably means just to determine the AXE formula and name the shapes, and he may ask for the bond angles as well.

Alexandra Albers 1D

Between two anions with a negative charge, I believe that if they both end up with the same number of electrons, the one with the greater negative charge has more polarizing power. For cations, if they both end up with the same number of electrons, the one with the greater positive charge is more po...

Alexandra Albers 1D

If you know the bond angles for the general shapes, I think that should be enough. I think that he said that knowing the exact angles would require looking them up usually.

Alexandra Albers 1D

I believe that a single unpaired electron goes to the oxygen because it is more electronegative than the carbon. The carbon then becomes the radical and, if it is surrounded by a single unpaired electron, a single bond, and a double bond, it has a formal charge of zero.

Alexandra Albers 1D

I don't think he has an exact set number established yet, but it will more than likely be between 6 and 8 problems.

Alexandra Albers 1D

The AXE structure in VSEPR theory is essentially just a template, so that if you can remember how one molecule with that particular structure looks, you will know the shape of all molecules of that model.

Alexandra Albers 1D

I believe that we will be expected to be familiar with how they look but we won't actually need to draw them ourselves. As long as we can identify them and know how the various shapes are made, I think we should be fine.

Alexandra Albers 1D

Also, since GeF4 has only bonded pairs of electrons, the bond angles are 109.5 degrees, but if there were unbonded electron pairs they would push the other atoms further away and make the bond angles smaller.

Alexandra Albers 1D

The only way in which the type of atom would affect the shape is in determining the number of electrons present and which atom is the central atom in the structure.

Alexandra Albers 1D

I believe that there is an equation to find electronegativity, however I don't think that we've been taught it. As long as you know that electronegativity increases across and decreases down the periodic table you should be good. If we need exact numbers, they will probably be given to us.

Alexandra Albers 1D

Can anyone tell me where we can check our grades for Chem 14A? I can find the tab on CCLE for my other classes, but I'm not sure where it is for this class.

Alexandra Albers 1D

Sb has only 5 valence electrons because its structure is [Kr] 5s^2 2p^3. You are counting the d-orbital which comes before it, which is the 4d row. The 4d row is full by this point, so it is lower energy than the 5s and 5p rows. Therefore, when you are removing electrons the 5p and then the 5s orbit...

Alexandra Albers 1D

It is usually the atom with the lowest ionization energy. Although if you are given the molecule, you may be able to figure out which atom is the central one based on if there is one type of atom and four of another type of atom for example, or a similar type of molecule.

Alexandra Albers 1D

I think that while we probably don't have to know details about electronegativity and such, we should probably generally know how the trends work and have an idea of them at least.

Alexandra Albers 1D

I believe that elements with higher electron affinities like to gain electrons to have a stable octet similar to a noble gas.

Alexandra Albers 1D

As of yet, we haven't needed to know how to determine the spin of a specific electron. We do know that in the configuration, electrons should be organized with parallel spins first though and then have the electrons of opposing spins added afterwards.

Alexandra Albers 1D

Shells refer to the quantum number n and can be 1, 2, 3,.... Orbitals refer to the more specific subshells of electrons, indicated by l. 1s, 2s, 2p,... are examples of orbitals.

Alexandra Albers 1D

On Dr. Lavelle's outline for the quantum world, it says we should be able to write the ground-state electron configuration for an element or ion (Aufbau Principle). We should probably know how to write at least a basic electron configuration, though I'm not sure how much of it will actually be on th...

Alexandra Albers 1D

I think that the work function depends on the problem, the equation with the work function is Kinetic Energy = hv - work function, so if you have the other values you can compute it that way, but I think otherwise some number for the work equation needs to be given in the problem. If that is the cas...

Alexandra Albers 1D

In the post-assessment for the video module on the Heisenberg Uncertainty Equation, there is a question where you are asked to calculate the electron's uncertainty in kinetic energy and then in kinetic energy per mole of electrons. I'm not sure exactly how to do this problem, so what equations shoul...

Alexandra Albers 1D

It does, thank you!

Alexandra Albers 1D

In the atomic spectra video, Dr. Lavelle says that -VE sign means that a bound e- has lower energy than a free e-. What does he mean by "bound" and "free" electrons?

Alexandra Albers 1D

c is a constant, and it is likely that the value of it will be given to us in the equation sheet provided by Dr. Lavelle, but it might be useful to memorize it anyway.

Alexandra Albers 1D

Test 2 is going to be in our discussion sessions starting from October 23, I believe.

Alexandra Albers 1D

This answer is correct, I believe. They have the same number of atoms and moles, so the number of moles for the answer is given by dividing the number of atoms present by Avogadro's constant.

Alexandra Albers 1D

In some questions, we are asked to write the formula of certain compounds, such as in question E.9 where it says to write the formula for magnesium sulfate heptahydrate. Should we memorize how to create some of these compounds or is it something we will get to know as the class goes on?

Alexandra Albers 1D

I think that for now, the best molar masses to use, if not given in the problem, would be the ones listed in the periodic table at the beginning of the textbook. If a problem gives you a number to use for an element's molar mass, then that would probably be the best number to use. I'm not sure if a ...

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