CHEMISTRY COMMUNITY

Nohemi Garcia 1L

If you're given the cell diagram, the cathode is usually on the right of the diagram and the anode on the left.

Nohemi Garcia 1L

Jessica Chen 2C wrote:Thanks for the response! Could someone summarize what knowing the type of system would tell you for each system? Like if it’s an isolated system, do I know that a certain value would be 0 or something?

The change in entropy is greater than or equal to 0 in an isolated system.

Nohemi Garcia 1L

I'm pretty sure that in case major technical difficulties occur, we can email Lavelle or our TAs just in case.

Nohemi Garcia 1L

Does anyone know if he's using the same grading scale as last quarter for 14A?

Nohemi Garcia 1L

I'm not sure if it's for all TA's, but my TA had us pick our tests up in her mailbox. Maybe try emailing your TA to see if they're also willing to do that?

Nohemi Garcia 1L

Julia Holsinger_1A wrote:When the equilibrium constant K is larger than 10^3 does the reaction favor the products or the reactants?

When it's larger it favors the products.

Nohemi Garcia 1L

Yes, definitely. Always check in case there's a typo or possibly a little "trick".

Nohemi Garcia 1L

No, it's never used for balancing in an acidic solution.

Nohemi Garcia 1L

I think it's better to know about these topics in depth, just to get a better understanding along with what Lavelle has gone over throughout the quarter.

Nohemi Garcia 1L

It relates to when you balance a redox equation, since they relate to charge. If an oxidation number/charge becomes more negative/smaller, then it means that there is a gain of electrons (Fe +3 ----> Fe +2). If it becomes more positive/larger, then there's a loss of electrons (Cr +3 ----> Cr +6). Re...

Nohemi Garcia 1L

Does anyone know if collision theory will be emphasized a lot in the final?

Nohemi Garcia 1L

If you were to increase the volume of a reaction, would it yield more products?

Nohemi Garcia 1L

I think that lecture notes and the textbook are fine. I don't think chemistry community is allowed though.

Nohemi Garcia 1L

I don't think that it's likely due to the formats of past finals/midterms. Since this situation different, it most likely a mix.

Nohemi Garcia 1L

Does anyone know if we'll get a review packet to work on even though reviews have been cancelled?

Nohemi Garcia 1L

As of now, I'm pretty sure we're taking our finals in the locations on the review sheet Lavelle gave us.

Nohemi Garcia 1L

It's independent if you see that the changes in concentration don't affect the rate. If you compare Experiments 1 and 4, you can see that only C changes in concentration, but the rate stays the same.

Nohemi Garcia 1L

I'm pretty sure they were written on our tests last week so it's likely that they'll be provided. It doesn't hurt to memorize them though.

Nohemi Garcia 1L

For this problem just use the first order equation, Rate=k[A]. Just find the concentration of N2O5 by converting the grams into moles, and then placing it over the amount in liters. Finally, all you have to do is multiply the k given with the concentration.

Nohemi Garcia 1L

You add platinum (s) or carbon (gr) when the anode and/or the cathode have no solid conductors in the cell diagram (they either have nonmetals or metals in an aqueous phase). As far as I know, platinum and carbon can be used interchangeably, but platinum is more common.

Nohemi Garcia 1L

In this case, since C is a zero order reaction (Rate=k), you won't really need to take C into account since its concentrations won't have any effect on the rate. Just solve for A and B as if C wasn't there.

Nohemi Garcia 1L

Why don't concentrations for zero order reactions matter? For zero order reactions, the differential rate late is just Rate=k. The concentrations aren't included in this calculation, so since C in this question is a zero order reaction, changing its concentration (like in Experiments 1 and 4) won't...

Nohemi Garcia 1L

Does anyone know why certain experiments are compared to each each to solve?

Nohemi Garcia 1L

I know that adding carbon is not as common adding platinum, but when would you need to add carbon (gr).

Nohemi Garcia 1L

I believe you add platinum to a cell diagram when the anode and/or the cathode need a solid conductor. How do we know/tell if the anode or cathode needs a solid conductor? We know we do based on the phases of the molecules. If it's just aqueous phases, then you'll definitely need one. Even in cases...

Nohemi Garcia 1L

Does anyone know if we are getting another review packet and if so does anyone know when it will be posted? Are the review sessions up as well?

Nohemi Garcia 1L

Is there a specific reason why the reduction part is written as Cl2 + 2e- ---> 2Cl - instead of using Cl2 as written in the problem?

Nohemi Garcia 1L

I remember hearing that Gibbs Free energy was going to be on it, and I think most of electrochemistry is fair game too.

Nohemi Garcia 1L

The anode is the part of the cell that performs oxidation, so the element/compound inside loses an electron. This electron transfers over to the cathode, which performs reduction and adds the electron to the corresponding element/compound inside. Just to add on: one way you can remember this is wit...

Nohemi Garcia 1L

I believe you add platinum to a cell diagram when the anode and/or the cathode need a solid conductor.

Nohemi Garcia 1L

Since oxidation occurs when an ion loses electrons (ends up having a more positive charge), you have to figure out the charges between the reactants and the products side. Like in Example 6K.1 (page 538), the oxidation half reaction is between C2H2O4 and CO2, because C goes from having a charge of +...

Nohemi Garcia 1L

H+ is added for balancing reactions in acidic solutions, and OH- is used for basic solutions. Just remember that in acidic solutions, only H+ is used for balancing H, while for basic solutions H2O is added to the side that needs H and add OH- to the other side of the reaction.

Nohemi Garcia 1L

When do you add carbon (graphite) as a conductor instead of platinum?

Nohemi Garcia 1L

The double lines just separate the oxidation half reaction and the reduction half reaction. The single line is just used to separate elements of different phases (gas/liquid/solid/aqueous solution) in a half reaction.

Nohemi Garcia 1L

There are some things to look out for when finding oxidation states: 1. The oxidation number for an atom in an elemental form is always 0 2.The oxidation number of of all Group 1A metals is +1, and Group 2A is +2, unless they are elemental. 3. Hydrogen is either +1 (when bonded to a nonmetal), or -1...

Nohemi Garcia 1L

You can tell by comparing the charges of the element as a reactant and as a product. The charges are either given directly in the chemical equation (like Fe +2) or are calculated (like with MnO4, which has an overall charge of -1, Mn is calculated to have a charge of +7 since the four oxygen atoms h...

Nohemi Garcia 1L

I'm pretty sure it extends into this week as well.

Nohemi Garcia 1L

Is there a reason why we balance a redox reaction with H2O and OH when it's a basic solution instead of just H2O and H?

Nohemi Garcia 1L

Study groups are also extremely helpful, as everyone can have different grasps on different topics.

Nohemi Garcia 1L

I'm pretty sure we can still work on thermodynamics, specifically Focus 5G.

Nohemi Garcia 1L

I'm pretty sure you're not alone on this; I'm having a bit of trouble too. I know peer leaning sessions help immensely, as the mentors are able to explain things in more detail and you can work in a small group at a time. Chemistry Community is also a great place for questions, and never be afraid o...

Nohemi Garcia 1L

He doesn't give any but if you are worried about grades you may be able to talk to him about it.

Nohemi Garcia 1L

For review sessions, just go to the ones you feel like you would need the most amount of help in. They are lots of them to help fit with everyone's schedule, so if there's a particular section you don't feel confident in, you can go to multiple of the same topic. I would highly recommend the review ...

Nohemi Garcia 1L

For those of you who have already taken the quiz, up to what subject do you recommend that we prepare for, and what topic should we put an emphasis on for studying?

Nohemi Garcia 1L

Doing all the homework problems does help in terms of practice. I also got a lot of help through peer learning sessions, as they were able to give a lot more practice and were able to clear up a lot of the material.

Nohemi Garcia 1L

Does anyone know why we have to multiply the concentration by 2 for part C? The solution manual says to do that, but I'm not sure if that's correct.

Nohemi Garcia 1L

In some problems, I've seen that ICE tables are used to solve for the equilibrium concentrations/partial pressures of reactants and products.

Nohemi Garcia 1L

K and Q are really similar when it comes to solving for them (they use the same formulas). Q however, can be solved during any point of a reaction, while K is only solved for at equilibrium.

Nohemi Garcia 1L

You can probably figure out which is going to be used if they use the terms "partial pressure" (which means that Kp will be used), or "concentration" (meaning Kc will be used). Kc is also used if the problem says that a certain amount of moles is mixed with a certain amount of so...

Nohemi Garcia 1L

The R is the gas constant, which is generally R = 8.314 J·K-1·mol-1. You can find it on the constants and equations sheet on the 14B website, along with its other conversions.

Nohemi Garcia 1L

Definitely do more than the required amount of homework assignments to get a broader sense of the topic, peer learning sessions, and studying with friends helps a lot. There are plenty of office hours so don't be afraid to go there, especially since we are able to go to all TA hours. Another thing t...

Nohemi Garcia 1L

In a way you can think about Le Chatelier's Principle as the homeostasis of a reaction. When something in the reaction changes, the reaction responds accordingly. If more reactants were to be added, the reaction would respond by forming more products. If more products were added, then more reactants...

Nohemi Garcia 1L

Does anyone know other examples of inert gases besides helium or argon, or are they all just noble gases?

Nohemi Garcia 1L

Another one is diethylenetriamine (dien), which is NH2CH2CH2NHCH2CH2NH2.

Nohemi Garcia 1L

I think an easy way to tell is to see if there are multiple atoms with lone pairs attached. Like with ethylenediamine, its nitrogen atoms have a set of lone pairs, allowing it to be a bonding site.

Nohemi Garcia 1L

Also as a quick tip, I believe you write the polydentate in parenthesis when using the prefixes.

Nohemi Garcia 1L

Tetrahedral I believe is one of these examples. It tends to be polar but in cases such as CH4, the structure become neutral. This is because all of the surrounding atoms are the same and their dipoles "cancel out."

Nohemi Garcia 1L

Working with others is always beneficial, since one person does not have the same information as another person, and overall helps with encouragement and support.

Nohemi Garcia 1L

I think the emphasis may be placed more on strong acids, but I would prepare for that anyway.

Nohemi Garcia 1L

What does it mean when dipoles "cancel out?"

Nohemi Garcia 1L

How does resonance affect the pH of an acid/base?

Nohemi Garcia 1L

Which coordination compounds do we for sure need to know for the final?

Nohemi Garcia 1L

Sigma bonds consist of two orbitals, one electron overlap from end to end, and can rotate. Pi bonds also have two orbitals with one electron overlap, but its side by side, and they cannot rotate.

Nohemi Garcia 1L

An amphoteric compound is one that shows both acidic and basic qualities. Like water, which is amphoteric, can react with acid to make a basic reaction, and with a base to make a more acidic counterpart.

Nohemi Garcia 1L

I'm not entirely sure, but I think it depends on the lone pairs within a molecule. Like water is a monodentate because it can only bond through oxygen which has 2 sets of lone pairs. With en (ethylenediamine) since it has multiple nitrogens with lone pairs, it is able to bond through multiple site, ...

Nohemi Garcia 1L

It's that, but when it's bonded to Fluorine, Oxygen, Sulfur, and nitrogen.

Nohemi Garcia 1L

For the oxidation numbers I just recommend keeping an eye out for negatively charged ligands.

Nohemi Garcia 1L

What do you do when your calculator cuts off a decimal before I get the required amount of significant figures? It's happened when my calculator decides to display the cut off decimal instead of the answer in scientific notation.

Nohemi Garcia 1L

I'm having trouble with quantum, since a lot of the problems require you to relate multiple equations with each other step by step. Does anyone have any tips on how to start, keeping your mind focused, and finding relationships between each equation?

Nohemi Garcia 1L

For these sets of problems, yes we want their overall charge to be neutral. Just remember that the coordination compound/ligands must have a charge opposite to the "outside" ion.

Nohemi Garcia 1L

If Lavelle posted that table himself, then I doubt that he would add some extra ones to the final. If you do happen to see one in the problems that occurs often but is not listed in the table, then it would be a good idea to write it down.

Nohemi Garcia 1L

For breakfast, do what works the best for you and don't make any huge changes the day off. Like if you normally do not drink coffee, don't try taking a large coffee the morning of. Fruit is always a good idea, and eat enough so that you don't get hungry during the exam.

Nohemi Garcia 1L

I feel like since quantum overlaps a lot anything should be fine. For sure look over equations and key constants.

Nohemi Garcia 1L

I say that for sure quantum and molecular shape/structure since we spent a lot of time emphasizing those.

Nohemi Garcia 1L

A ligand is a polydentate when there are multiple molecules to that one ligand (like NH2CH2CH2NH which is a bidentate).

Nohemi Garcia 1L

Definitely look over quantum, since it was a large emphasis during the first half of the quarter.

Nohemi Garcia 1L

I would say look over any review sheets that were already given to us to refresh our memories on everything that we went over in the beginning. Also forming study groups with people helps a lot since everyone gets to help each other out. Also, if there are still some concepts that still don't make s...

Nohemi Garcia 1L

Neutral ligands include H2O (aqua), NH3 (ammine), NO (nitrosyl), CO (carbonyl), NH2CH2CH2NH (ethylenediamine), NH2CH2CH2NHCH2CH2NH2 (diethyltriamine).

Nohemi Garcia 1L

Another idea would be to redo the midterm questions. Since we got the test packet back, it wouldn't hurt to look over which problems we missed and get extra practice for what we went over at the beginning of the quarter.

Nohemi Garcia 1L

A neutral atom? If you determine its formal charge, you'd use the equation (5-(2+6/2), which would equal 0. I'm guessing you're meaning non-polar or polar, and I believe that it is polar, since it's a tetrahedral molecule that doesn't have the same 4 atoms bound to its electron-dense regions. The m...

Nohemi Garcia 1L

There isn't a way to calculate bond angles (or at least in this course) because the exact angles are found experimentally. I think you will be fine if you just memorize the general bond angles given for each shape.

Nohemi Garcia 1L

It's linear. There are no lone pairs on the central atom and it has 2 areas of electron density (VSEPR formula: AX2).

Nohemi Garcia 1L

You could also ask Lavelle since he is making our final to double check.

Nohemi Garcia 1L

Seesaw occurs when a molecule has 5 areas of electron density and 1 lone pair (VSEPR formula: AX4E1).

Nohemi Garcia 1L

You leave it as a regular p orbital since it technically wasn't hybridized.

Nohemi Garcia 1L

A molecular shape is a seesaw when the molecule has 5 areas of electron density and 1 lone pair. Tetrahederals have 4 areas of electron density and no lone pairs, but t shapes either have 5 areas of electron density and 2 lone pairs, or 6 areas of electron density and 3 lone pairs. (Basically t shap...

Nohemi Garcia 1L

There are times when the central atom has a positive/negative charge but that's only when the molecule has a positive/negative charge.

Nohemi Garcia 1L

The main idea behind the equation is to find the location of an electron and its probability finding it at a certain point.

Nohemi Garcia 1L

I would recommend paying attention to the sig figs in a problem to avoid losing points on the midterm.

Nohemi Garcia 1L

Resonance structure are basically like the synonyms of chemistry; it's when there are multiple ways to draw a lewis structure for a molecule.

Nohemi Garcia 1L

When you draw a lewis structure you have to pay special attention to the valence electrons in each atom; they help determine if there are single/double/triple bonds. There is normally a center atom, and that is normally the atom that has the lowest ionization energy. For bonds (when the molecule is ...

Nohemi Garcia 1L

Can anyone explain why and how the equations c=lambda*frequency and E=hv are combined (E=c*h*lamdba^-1) to solve for this answer? I honestly don't understand how this works.

Nohemi Garcia 1L

I also talked to my PLF about midterms today, and she said this midterm could be more quantum heavy. It's a possibility but it doesn't help to study more on this subject.

Nohemi Garcia 1L

It works for problems that ask for the wavelength but list a momentum (m/s) instead of a frequency. As others have mentioned already, it is pretty similar to the equation, c=lamda*frequency; just be careful not to confuse the two.

Nohemi Garcia 1L

Just a thought, but if you think that there should be more modules, then you should ask Lavelle so he can post them for later terms.

Nohemi Garcia 1L

Will the specific sig fig range be given before/in the test?

Nohemi Garcia 1L

Does anyone know if we have to provide our own periodic table for the test?

Nohemi Garcia 1L

In a problem, sig figs would probably just be mentioned for rounding, like in keeping the final answer a certain number of sig figs.

Nohemi Garcia 1L

I think some of the molecular formulas are given to us, such as the "less common ones", whereas compounds like carbon dioxide which are "more common" will not.

Nohemi Garcia 1L

The 100 gram method is especially useful for when the problems don't give a specific mass for a molecule, but it gives the mass compositions. Just be careful when there is a specific mass given for a molecule; the 100 gram method probably won't work.

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