CHEMISTRY COMMUNITY

Charlotte Adams 1A

YuditGaribay3J wrote:So when we are looking at oxidizing agents it is just the opposites of what we think it is. So normally I think of oxidizing as losing but it is actually gaining? and vise versa?

If you put it that way then yes.

Charlotte Adams 1A

If you have a reaction that has a negative gibbs free energy, but the reactant does not turn into the product, then the reactant is kinetically stable

Charlotte Adams 1A

Change in internal energy is zero for an isolated system.

Charlotte Adams 1A

Amines contain a nitrogen atom with a lone pair.

Charlotte Adams 1A

Kamille Kibria 2A wrote:im not sure if this diagram helps but this is what I did. you just add up the reverse delta H and activation of the forward reaction. we have different numbers but it's still the same concept

This is so helpful!! Thanks

Charlotte Adams 1A

I believe you are usually given the delta H of fusion or vaporization, at least thats how it was on the previous tests. Is this a book problem? Maybe you have to look at an appendix?

Charlotte Adams 1A

You got this!!!Just keep reminding yourself that you have studied, that you are prepared, and it is just one test.

Charlotte Adams 1A

There are some good meditation apps that have segments on test anxiety and school anxiety that I find helpful. Try the Calm app, its great!!

Charlotte Adams 1A

I schedule my day in advance and make sure to at least give myself an hour of down time.

Charlotte Adams 1A

I Know Lavelle derived them in class but I found the book to be really helpful for these equations.

Charlotte Adams 1A

Is it still from 2-4?

Charlotte Adams 1A

IM SO EXCITED

Charlotte Adams 1A

Hello! The reaction mechanism as, Dr. Lavelle mentioned, is simply the number of steps that take place as reactants go to products. In regards to your second question, the overall rate law is determined by the slowest step, also known as the rate-determining step, because the other steps following t...

Charlotte Adams 1A

No, you don't multiply by the stochio coefficients. Could you let me know your procedure for this question? I got E⁰ to be 3.878 using Red potential of Au3+ minus Red potential of Mg2+ = 1.498-(-2.38)=3.878 Keep in mind though that this question is asking you for delta G and not E⁰ Thanks for your ...

Charlotte Adams 1A

Could someone help me find the E∘cell of this eqn? I have tried it a couple times but have not been able to get it. Do I need to multiply by the stoich coefficients?

Thanks in adnavce

Charlotte Adams 1A

When balancing a half reaction that is in a basic solution, should you balance the oxygen before the hydrogen? For example, how should I go about balancing the half reaction in the picture below?

Thanks in advance

Charlotte Adams 1A

Can someone explain what a reducing agent does and what an oxidizing agent does? Also how do you know what is the reducing agent and what is the oxidizing agent when given a chem eqn?

Thanks

Charlotte Adams 1A

Can someone tell me what I am missing for the balanced equation. I wrote the half reaction and added H2O and OH when I thought it was necessary but I think they cancel out, am I wrong?

Charlotte Adams 1A

This problem is asking us to determine how the oxidation numbers have/haven't changed across the reaction. Starting with KClO2, we know that the oxidation number of O is 2- (from the periodic table) and that the oxidation number of K is +1 (from the periodic table). From that we can deduce an equat...

Charlotte Adams 1A

There are a few rules that you can follow. First, any neutral element that is not a part of a compound (such as O2 in this problem) will always have an oxidation state of 0. Second, oxygen and hydrogen usually have oxidation states of -2 and +1, respectively, when attached to any compound. So for t...

Charlotte Adams 1A

Hello, I know this is supposed to be a pretty easy question but could some one help me figure out the oxidation states for this problem and maybe explain how they figured it out? Thanks in advance.

Charlotte Adams 1A

steps #1-identify species being reduced/oxidized #2-write skeletal eqn. #3-balance all elements except O and H #4- basic solution=balance O by adding H20, then balance H by adding H2O and then add OH to other side #5-balance electrical charges by adding electrons where it is appropriate #6-multiply ...

Charlotte Adams 1A

I thought the same thing but I think the book wants us to calculate the standard entropy as the water temp rises, calculate the entropy for the vaporization of water, then calculate the entropy for it to cool back down to 85 degrees. Basically, the book is just unclear in their directions

Charlotte Adams 1A

Arya Adibi 1K wrote:As stated by Chem_Mod, Whenever a conducting electrode is needed, use Pt.

You would need a conducting electrode whenever either the reactants or products are aqueous and don't have a solid conductor.

Just to clarify, can a conducting electrode be an anode or a cathode?

Charlotte Adams 1A

Think of the bicycle example from lecture. If we push air into bike, we are doing the work and the bike is gaining work.

Charlotte Adams 1A

I think the solution is just aqueous

Charlotte Adams 1A

I stayed up cleaning to destress.

Charlotte Adams 1A

Thermodynamically Favorable just means that the gibbs free energy is negative

Charlotte Adams 1A

Its used to find the equilibrium constant at some temperature if we know the equilibrium constant for the same reaction but at a different temperature.

Charlotte Adams 1A

Without the salt bridge the solution with the anode will become positive and then the electrons will not want to flow toward the cathode.

Charlotte Adams 1A

LeanneBagood_2F wrote:wait what exactly are bomb calorimeters? has this mentioned in lecture before? if so, when/where and how solid should we be on this topic?

I believe it was mentioned in lecture 12 but it may have been lecture 11. I know its in one of the two.

Charlotte Adams 1A

Try converting kelvins to degrees Celsius by subtracting 273.15

Charlotte Adams 1A

use the formula ΔS=nCvln(T2/T1)

Charlotte Adams 1A

Think of Lavelle's example of the bicycle pump. When the system is being compressed we are putting work into system so the system gains work.

Charlotte Adams 1A

Heather Costa 2C wrote:wait actually it just used to help find the temperature when it is unknown?

Yes, it helps us find the temperature that is needed for reaction to be either spontaneous or nonspontaneous

Charlotte Adams 1A

I am a little confused because for one of the sapling questions we had to calculate using the irreversible path equation and the reversible path equation.

Charlotte Adams 1A

Use stoichiometry to find the moles of N2 and then plug into PV=nRT, also I think you will have to convert your final answers to joules.

Charlotte Adams 1A

It is called reversible because the process can be reversed by a a small change.

Charlotte Adams 1A

I think sapling questions are useful and a good way to test your knowledge, especially because the solutions are right there and do a good job of describing how to solve the problem.

Charlotte Adams 1A

I plan my entire day and put aside some time to relay at night. I have recently discovered that I enjoy painting and it calms me down.

Charlotte Adams 1A

I thought of it more in terms that the total heat had to be heat required to melt ice + q (ice) + q (water), then I plugged in and solved the equation.

Charlotte Adams 1A

If you drew the lewis dot structure for N2 or if you remember VSEPR you wold be able to find the shape.

Charlotte Adams 1A

I'm currently taking 14BL virtually with Dr. Casey, and while I do regret missing out on the experience of an in-person lab, I would say that the class itself has been enjoyable. I learn best in a hands-on environment, so my lab skills will likely be shaky after only learning through videos and sim...

Charlotte Adams 1A

Inert gases have no effect on pressure, compressing the system changes the pressure and thus K.

Charlotte Adams 1A

I understand how you feel and it is not a good feeling. Luckily, we have another midterm and a final so we have the ability to raise our grades. Also, chem community and hw are really easy points that add up which helps.

Charlotte Adams 1A

If the reaction is endothermic, increasing temp will increase K because more products have formed
If the reaction is exothermic, increasing the temp will decrease K because more reactants are formed.

Charlotte Adams 1A

My guess would be at least a week to two weeks.

Charlotte Adams 1A

Also, I believe for weak acids/bases x is insignificant because you know that because they are weak, they will have a K value that is considered small.

Charlotte Adams 1A

I'm currently taking 14BL virtually with Dr. Casey, and while I do regret missing out on the experience of an in-person lab, I would say that the class itself has been enjoyable. I learn best in a hands-on environment, so my lab skills will likely be shaky after only learning through videos and sim...

Charlotte Adams 1A

The C and H2 were omitted because they are already in their standard state. Also I am pretty sure we will be given standard enthalpies of formation of each reactant and product on midterm.

Charlotte Adams 1A

Yes, it is included in the equation unless it is unless it is a pure solid or liquid.

Charlotte Adams 1A

I believe that you are correct that the equilibrium concentration of the reactants would be larger to maintain the equilibrium constant.

Charlotte Adams 1A

We might get the delta H and be asked what would be favored if there was a temperature increase/decrease.

Charlotte Adams 1A

Are you sure that the initial concentration is what causing you to get this problem wrong? What did you do to get your answer?

Charlotte Adams 1A

I think the rule of the percentage being over 5% applies to percent ionization and percent protonation.

Charlotte Adams 1A

I think, like the others said, that he was referring to iodine as i2.

Charlotte Adams 1A

Is the exam proctored by our TA?

Charlotte Adams 1A

Stronger acid= higher Ka, lower pKa
weaker acid=lower Ka, higher pKa

Charlotte Adams 1A

I assume we will only be given problems with elements that we know the standard state for. So like diatomic molecules and carbon.

Charlotte Adams 1A

Im not exactly sure but I know that breaking the bonds of a liquid to get a vapor requires energy so for the opposite to occur energy is released.

Charlotte Adams 1A

I believe that is correct because I know that for an acid/bas reaction Ka*Kb=Kw which is the constant for the autoprotrolysis of water

Charlotte Adams 1A

It also helps to eliminate the equations you know that you are not gonna use. For example the one equation had Cl but that was not in our final equation so we know that we don't need that equation.

Charlotte Adams 1A

Yes, you do the same ICE table and procedure as you would if given concentration and I remember Dr. lavelle saying 1 bar= 1atm

Charlotte Adams 1A

I thought it would be during discussion like last quarter, but people in my discussion said that it was during class on January 29th.

Charlotte Adams 1A

Does someone mind explaining what to do witht he reverse of that question ^? Like when you end up with two negative answers. Or is that typically a red flag and the work should be checked? I think you want to check that because usually X is the concentration of some reactant or product and a concen...

Charlotte Adams 1A

if the rxn shifts to right, the reactants decrease and the products increase. If the reaction shifts to left, the reactants increase and the products decrease.

Charlotte Adams 1A

The pressure increase we are referencing is the pressure increase that occurs when the volume is decreased. This causes the reaction to shift because my changing the volume, we are changing the concentration of the reactants and products and this causes the reaction to no longer be in equilibrium.

Charlotte Adams 1A

We would need to be given if the reaction is endothermic or exothermic. I assume we will either by told or given delta h.

Charlotte Adams 1A

the reaction quotient expression has the same form as expression K, but it refers to any stage of the reaction

Charlotte Adams 1A

When volume decreases and the pressure increases, the reaction will shift in the direction that reduces the number of molecules

Charlotte Adams 1A

The only thing that will change the equilibrium constant, k, is temperature. However when you increase the pressure by decreasing the volume, the concentration increases and the reaction will thus proceed to the left or right in order to return to equilibrium.

Charlotte Adams 1A

Harry potter!!

Charlotte Adams 1A

For problems like these, you first have to look at all of the molecules that make up the products and reactants, in this case that is NH3, 3I2, N2, and 6HI. Then, you can look at the one step equations given and make note of the ones that contain the molecules you got from step one. Then, from the ...

Charlotte Adams 1A

You can also think of it in terms of Q, if you remove product then Q will be less than K and we know when that happens that the system will proceed to the right/make more product.

Charlotte Adams 1A

Im not positive but I think that because reaction is going in opposite direction, you have to set it equal to 1/K

Charlotte Adams 1A

I think if K is greater than 1 that means the product is more stable than the reactant because there is a higher concentration of product than reactant. Same for if the reactant is higher than the product.

Charlotte Adams 1A

The reaction will proceed to the right and the excess reactant is turned to product.

Charlotte Adams 1A

Just to add to what everyone else has said, Q=K when the reaction is at equilibrium.

Charlotte Adams 1A

I had the same problem and it wouldn't let me use my credit so I logged out and logged back in then it worked. Also I had a sapling problem last quarter and had to call them, the IT people at sapling are pretty helpful.

Charlotte Adams 1A

I believe the values will be different but if you need to convert one to the other you can use the equation PV=nRT.

Charlotte Adams 1A

Products will be plus X because as they reaction takes places products are formed. Reactants are minus X because as the reaction occurs the reactants are being used to form the products

Charlotte Adams 1A

I would read the textbook lessons he assigns and make sure to both the sapling questions and DO THE TEXTBOOK questions even though it is not mandatory. They often show up on the exams. Also make sure you understand the concepts behind the math and not just how to plug the numbers into the equation.

Charlotte Adams 1A

Some of the problems we have done included them, but my guess is if they are part of the problem that the question will say what each represents.

Charlotte Adams 1A

I believe we do not know and I don't think we would be asked to identify. I think we should just know that if a coordination compound has a coordination number of 6 it is an octahedron and if it is four it can be tetrahedral or square planar.

Charlotte Adams 1A

I believe that equation is only used in a one electron atom and it would be used if we wanted to find the energy absorbed or released.

Charlotte Adams 1A

I believe an oxyacid is just an acid that contains oxygen, like HNO3 or H2SO4

Charlotte Adams 1A

I think just know that they can donate more than 1 hydrogen proton and they include H2S04, H2CO3, and H3PO4

Charlotte Adams 1A

LeanneBagood_2E wrote:What about when you're presented with the names+prefixes already and you have to find the opposite?
Like, does the order you write the ligands/formulas in the square brackets matter?

My TA said that it doesn't but I think you would just do it alphabetically.

Charlotte Adams 1A

if you know what (en) stands for you will be able to tell if it is a polydentate ligand by the name of the compound.

Charlotte Adams 1A

If a complex has a coordination number of four, a seesaw shape would not be the most stable structure because the atoms are not as far from each other as possible, like in a tetrahedral or square planar shape.

Charlotte Adams 1A

I believe diamagnetic just means that there are no unpaired electrons

Charlotte Adams 1A

If a a pi bond is present that means that a sigma bond is also present.

Charlotte Adams 1A

Drawing the shape of the molecule and the dipole moments will help because it will show if the dipole vectors cancel out.

Charlotte Adams 1A

I think as long as we can name the ligands we used in class examples, in the sapling hw, and in the textbook problems, we will be fine.

Charlotte Adams 1A

Ligands attach to a transition metal in a coordinate covalent bond. If there are 6 ligands connected to the transition metal it is an octahedral Copley and if there are 4 ligands attached it is either tetrahedral or square planar complex.

Charlotte Adams 1A

You can use the group number to determine the number of valence electrons or you can figure out the electron configuration but that takes a while.

Charlotte Adams 1A

Can someone explain why the bond angles about the carbon atoms for the molecule (CH3)2Be are 109.5 degrees. Shouldn't it be less than 109.5 because Be pushes the H atoms further away from it than a H atom would?

Charlotte Adams 1A

The elements closest to Fluorine have a higher electronegativity.

Charlotte Adams 1A

I was also confused and still am, but the solution says molecules of this type can be explained by the formula H2CC(x)CH2 and if X is an odd number the H atoms at end of molecule will lie on perpendicular planes.

Charlotte Adams 1A

I just know that the hybridization numbers have to add up to the atomic orbitals and that s can only go to 1, p to 3, and d to 5. So if there are 5 atomic orbitals I know it is sp3d, because 1+3+1=5.

Sorry if this is confusing.

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