CHEMISTRY COMMUNITY

Olivia L 4E

How do I determine if this reaction is endothermic or exothermic? It gives the reaction constants of the forward and reverse (so you know the equilibrium constant) and the activation energies for both.

Olivia L 4E

Just want to confirm, is the total cell potential (voltage) always positive for a galvanic cell? Cathode/anode can be positive or negative though right?

Olivia L 4E

If a reaction has activation energy, is it always endothermic? If not, is it because deltaG plus the activation energy is still less than zero? or is there something else?

Olivia L 4E

The unique rate is a essentially a proportion that gives you the rate of each product/reactant relative to the other. It is the rate of the product or reactant divided by its stoichiometric coefficient. Lavelle gave an example in class that makes a lot of sense. If the equation is 2NO2 ---> 2NO + O2...

Olivia L 4E

Why is the rate constant k not negative for second order reactions?

Olivia L 4E

Ohhh okay thank you so much!!

Olivia L 4E

Also what is/are the underlying key concept(s) that we should take away from the various rate laws?

Olivia L 4E

Are rate laws simply referring to the rate at which a concentration increases or decreases? What's the difference between integrated versus differential?

Olivia L 4E

So I could be completely wrong as my response is in disagreement with the two answers before me, but I was told that when you have electrons in the reactant side, this is the reduction half of the reaction because it has GAINED electrons. Oxidation half is when the electrons are in the product side ...

Olivia L 4E

I'm assuming this example was describing the reduction half of the reaction? The form goes as follows oxidation solid (anode) | oxidation gases/liquids | oxidation aqueous solutions || reduction aqueous solutions | reduction gases/liquids | reduction solid (cathode). As you read from outward in, the...

Olivia L 4E

First you should write out each half reaction and determine which is the reduction and which is the oxidation components. Oxidation occurs in the anode (left) while reduction occurs in the cathode (right). That being said, your cell diagram corresponds to this order: oxidation on the left and reduct...

Olivia L 4E

From what I've heard from friends who've taken BL already is that the labs can be pretty tedious and time-consuming but mostly consist of busywork. If you feel that your other classes are going to be too strenuous to add extra work, then I would hold off on taking it. 14C, 3C and a GE don't seem lik...

Olivia L 4E

K depends on temperature, K being when the system is at equilibrium. When a system is at equilibrium, deltaG equals zero.

Olivia L 4E

The standard conditions for measuring Gibbs Free Energy are constant pressure and constant temperature. A negative deltaG reflects a spontaneous, exergonic reaction because it releases energy while a positive deltaG reflects a non-spontaneous, endergonic reaction as it requires energy.

Olivia L 4E

Jason Ye 2I wrote:Entropy is equal to zero in a perfect crystal at T= 0K

This is for residual entropy (3rd Law of Thermodynamics) but if you are asking for when delta S = 0, that's entirely different and occurs when the system is reversible and returns to its original state.

Olivia L 4E

In the equation for degeneracy, W=(number of potential positions)^(n) in which n represents the number of molecules. This is because the base (number of positions possible) already accounts for the atoms and their positions so n dictates how many molecules there are that you need to take into consid...

Olivia L 4E

When do we get our midterm scores back?

Olivia L 4E

Does kb equal nR??? Also what is capital W representing and what is kb?

Olivia L 4E

kamalkolluri wrote:w = -P(deltaV) by definition. So an increase in volume (expansion), makes dV positive, so the work done is negative. However, if deltaV is negative (compression), then work is going to be positive (compression).

THANK YOU this immensely cleared things up for my friend and I.

Olivia L 4E

For 4A.3 in the seventh edition, why is work a positive value? like what value in the work equation is negative to make cancel out the negative that's already there? And also, how do I determine logically (without an equation) if work is a positive or negative value? eq. w = -(2atm)*(pi)*(2cm)*(1.5c...

Olivia L 4E

As stated above, Kp is designated for gases because it is the equilibrium constant for partial pressure, hence the p. On the other hand, Kc can be used for both aqueous solutions and gases as it is a measurement of concentrations, usually mol/L.

Olivia L 4E

How much detail do we need to know about bomb calorimeters and such?

Olivia L 4E

I just wanted to confirm that we've learned everything from the "Thermochemistry" section right? And just began the "thermodynamics" section?

Olivia L 4E

To add to the previous reply, the brackets used when writing out the K equation indicate concentration so in doing that represents mol/L.

Olivia L 4E

In the 6D section of 7th edition book, for calculating pKa/pKb and Ka/Kb, I didn't round until the end and got a number close to what the answer was. I tried it again by rounding after every calculation then got the answer the book indicated. The book has been incorrect time and time again in regard...

Olivia L 4E

The number of significant figures in pH is equal to the number of digits after the decimal point, I was just wondering if this was the same rule for pKa? I didn't think so but my book solutions keep following that rule. Then again, my 7th edition tends to use the wrong sig figs frequently.

Olivia L 4E

Do you remember the Lewis structure diagrams Lavelle drew in class? They are depicting the formation of H3O+ and OH- ions (ionizations). The ionization constant of water refers to level at which H3O+ and OH- are equal. 10^-14 is the equilibrium constant of the chemical reaction so 10^-14 = [H3O+][OH...

Olivia L 4E

Definitely everything on Chemical Equilibrium will be on there and I'm pretty sure it will also all of Acid & Bases. You should check the class website outlines for more details on the two. I'm assuming it will cover Acids & Bases because we've already learned to do just about everything on ...

Olivia L 4E

It is squared because the equilibrium equation is [N2][O2]/[NO2]^2. The change in concentration is denoted as p. Because N2 and O2 began with zero initial concentration, you simply use 0+p to get p as the equilibrium concentrations for both. The problem simplified it further by substituting the p in...

Olivia L 4E

They are exclude because the equilibrium constant describes concentrations/partial pressures whereas solid has neither. Liquids have a concentration but act as a solvent so they aren't included. Aqueous solutions on the other hand, are the solute so they are included because they are a by-product.

Olivia L 4E

As you probably know, K represents the equilibrium constant. The subscripts specify what the equilibrium constant consists of. Kc means the equilibrium constant of concentrations whereas Kp means the equilibrium constant of the partial pressures. You use Kp when the equation includes just gases just...

Olivia L 4E

This is a basic equilibrium constant question, but I'm confused on why the answer for this has a "P" then the chemical formula whereas in class we didn't do that. Do we need the "P" and what does it even mean?

Olivia L 4E

If given a figure, you can tell if the ligand is bound to the TM in more than one spot and then count the number of bonds. If not given a figure, you just have to memorize it (this is what a TA just told us in a review session). The ones we need to know are ox (2), edta (6), en (2), and dien (4).

Olivia L 4E

Amphoteric means to display both acidic and basic characteristics. They can act as an acid or a base. An example is water.

Olivia L 4E

We don't need to know this for our final but I believe they are inorganic.

Olivia L 4E

So when determining polarity and dipole, you need to look at the atoms' electronegativities. Oxygen is more electronegative than sulfur so electrons are pulled towards the oxygen atoms. When considering the lone pair electrons, they are negatively charged and actually contribute to electron repulsio...

Olivia L 4E

Keep in mind that when determining the orbital hybridization, you are focusing on the number of electron densities. This where the d oribital will come into play (for octahedrons and square pyramidals). If this is the case, then the composition will be (ELEMENT 2sp3d2, ...).

Olivia L 4E

I just asked my TA this today and he said it would be (Cp -Cp) because they are the same type of bond. The compositions are the same but there are more than one.

Olivia L 4E

When and if we are asked to draw out molecule in their correct molecular shape, it has to be in 3-D right? My concern is that the 3-D figure will look wrong if we draw it poorly.

Olivia L 4E

When determining the shape of a molecule, all the regions of electron density need to be taken into account. They must be spread as far apart as possible in order to make the structure more stable (close together causes e- repulsion and therefore instability). Since lone pairs are regions of e- dens...

Olivia L 4E

In a molecule, the atoms surrounding the central atom have some degree of electronegativity (the "hogging" of electrons when sharing). This creates a dipole moment. If the shape doesn't allow the polarity (pull of the electrons and difference in charge) to cancel each other out, it will be...

Olivia L 4E

Yes, the above statement is correct regarding the electronegativity trend. The noble gases, with the exceptions of Xe and Kr that sometimes bond with fluorine and highly reactive elements, do not have electronegativity values. Those two exceptions are not of much importance though.

Olivia L 4E

Dr. Lavelle hasn't gone over this with us yet so this could be a part of Wednesday's lecture or it may not be something we learn how to calculate in this class. For now, I would suggest just memorizing (it will probably be on the formula page though) until further notice from Lavelle.

Olivia L 4E

Yes they can be the same length. This would indicate that this Lewis structure is a resonance structure. We all know double bonds and single bonds are not equivalent so if the structure shows they are, this means the electron is delocalized and shifts from one atom to another in the middle.

Olivia L 4E

My friend said she got chem material from the test bank, but I don't think it's from Lavelle's tests. There are several worksheets on here, Chemistry Community, from step ups and such other than the Garlic Bread one.

Olivia L 4E

For question 12c, why is it better to have a triple bond with the two nitrogen atoms instead of double bonds on nitrogen and oxygen? The charge is both the same.

Olivia L 4E

The midterm is just covering material up to Wednesday's lecture correct? So we don't have to know electronegativity and everything else from Friday's lecture?

Olivia L 4E

Parallel shells are electrons with the same spin (up or down) in different orbitals but the same subshell. As a result, the only differing quantum number is ml. Electrons cannot have the same spin in the same orbital because that would give them identical quantum numbers.

Olivia L 4E

Is a covalent or ionic bond stronger? I've heard people argue both. Also why is it that one?

Olivia L 4E

This is one of the exceptions Lavelle discussed in lecture. It's called the "Full d^10" exception because usually the 4s has lower energy level (4s before 3d) but this case it does not and the 3d has all elections and is full.

Olivia L 4E

Is everything from The Quantum World going to be on Test 2? If not, which concepts are we NOT going to be tested on?

Olivia L 4E

So I wasn't able to make Friday's lecture and I was looking at my friend's notes, but I'm really confused. Can someone explain the Shrondinger equation and the concepts behind it please!

Olivia L 4E

The probability is psi squared because of the Born Rule. This rule states that "the probability of obtaining any possible measurement outcome is equal to the square of the corresponding amplitude."

Olivia L 4E

This doesn't apply to "properties of light," but does anyone know when we will receive our results from test 1 and if we will be able to go over our answers?

Olivia L 4E

Where does the R come from in this equation (En=-hR/n^2)? Since it's Rydberg's constant, does it just have to do with proportionality like Planck's constant?

Olivia L 4E

A mole isn't referring to a specific type of unit; instead, it is a numerical representation of whatever object, unit, etc. is at hand. There are 6.022 x 10^23 objects of whatever your measuring. This could be atoms, molecules, Joules, etc. It's just a measurement similar to how a "dozen" ...

Olivia L 4E

What I usually do is round the molar mass to the number of sig figs in the initial problem. By initial problem, I mean the number amount given in the question. If there isn't one given, probably stick to the molar mass of the periodic table.

Olivia L 4E

Yes, you just multiply the two because theoretical yield is in grams so by multiplying 81g.mol-1 and 0.20 mol, you get 16.2g. Basically, the student will have 0.2 mols of product, the expected and theoretical results if nothing alters the reaction. If the product has a molar mass of 81g.mol-1 and if...

Olivia L 4E

Can someone explain Step 5 of "Solving a Stoichiometry Problem" more in depth please?

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