CHEMISTRY COMMUNITY

Arnav Saud 2C

Salt bridges allows the neutrality of the cell to be maintained by allowing electron flow through the cell.

Arnav Saud 2C

I think knowing the relationship of how equilibrium can change in terms of the Laws for Le Chatelier's Principle is important. (Changing temperature, pressure, volume, amount of reactants or products and how it will effect the way the system will act.)

Arnav Saud 2C

Q is mainly used to compare which side is going to be favored in relation to Q.
You'll probably have to find Q using some initial molar concentrations, then compare it to K.

Arnav Saud 2C

q is normal heat, while q rev refers to the heat of the reversible expansion.

Arnav Saud 2C

State property can be described as a property in which the pathway that was taken is not accounted for/does not matter. It's kind of like if you travel to two different cities, but take some extra trips along the way. The only thing that matters is the net difference between the distances of the sta...

Arnav Saud 2C

I don't think third order reactions will be covered on this exam. We'll only cover 0-2 order reactions.

Arnav Saud 2C

Thermodynamics deals primarily with the stability/spontaneity of a reaction.
In kinetics, you focus speed/rate of the reaction.

Arnav Saud 2C

Since B is a second order reaction, it will change by a factor of [3]^2 = 9

Arnav Saud 2C

You should stick with kelvin because most of the common/most used constants in this class use kelvin.

Arnav Saud 2C

In order to calculate half life of a zero order reaction, you would want to use the t_1/2 = [A]₀/2k.

Arnav Saud 2C

Salt bridges help maintain the neutrality of the charges in the system.

Arnav Saud 2C

For this homework assignment, put the phases of matter in unless not specified.

Arnav Saud 2C

So for this one, It gives you the half reactions already so, I think what you're supposed to do first is add the electrons to the half reactions. The Cu reaction would be: Cu ---> Cu^2+ + 2e- The Ag reaction would be: Ag+ + 1e- ---> Ag Then, you'll want the electron numbers to be equal so multiply t...

Arnav Saud 2C

Lets say we have an anode reaction of: Pb + 2Cl- -rev-> PbCl2 + 2e- And a cathode reaction of: 2AgCl + 2e- -rev-> 2Ag + Cl- For this reaction of the cell, the short hand notation would be: Pb|PbCl2|Cl-||Cl-|AgCl||Ag On the left hand side, you want to show the reaction that is occurring in the anodes...

Arnav Saud 2C

When work is done on the system, it's positive.
When the system does work, it's negative.

Arnav Saud 2C

For this problem, the first thing you want to do is find the reduction potential values of the anode and cathode.
You then want to use the E = cathode - anode.
After you find that, you want to use the delta G = -n*F*E equation.
Also, note that n = moles of electrons are transferred in this reaction.

Arnav Saud 2C

State properties are essentially properties where you do not need to know the intermediary steps that resulted in the final value being produced. A good example is the one that Dr. Lavelle provided in class where you're going hiking up a mountain. Let's say you're going from 5000 feet to 6000 feet. ...

Arnav Saud 2C

When working with the gas constant R, the most important thing you need to look at are the units that you have and the ones you need to find. For example, if you know the pressure, temperature, mass(in mols) and need to find the volume, you'll want to use the 8.206E-2 value.

Arnav Saud 2C

When work is done on the system, it's a positive value because energy is being directed to the system. When work is done by the system, it's a negative value because the system is expanding/expending energy.

Arnav Saud 2C

I think the best way to think about it is the way it's situated.
If K is used as a unit, then it's most likely kelvin. If K is equaling some kind of value or is involved in an equilibrium problem, then it's probably referring to the equilibrium constant. A lowercase k refers to the Boltzmann Constant.

Arnav Saud 2C

Cell potential isn't a state function because knowing the path of the system is necessary.

Arnav Saud 2C

For state properties, the most important thing to account for is whether or not the property is only dependent on the final and initial state. Entropy and enthalpy are good examples of this.

Arnav Saud 2C

a) First you want to convert the 80 degrees celsius to kelvin which makes it 353 degrees kelvin. The equation you want to use for this problem is deltaH = T*deltaS. We know the entropy of vaporization is 85 J/K and we know the degrees kelvin for the problem is 353 degrees kelvin so plug the values i...

Arnav Saud 2C

For 4I9a) The total entropy change is given by deltaS surr + deltaS for an isothermal, reversible process. This means we need to use this equation: deltaS = nRln(V2/V1) We need to find n so use the PV = nRT formula. After you find n, plug it in and all of the other given information into deltaS = nR...

Arnav Saud 2C

The enthalpy, entropy, and gibbs free energy equations are all state functions.
Work and heat are not state functions though. (deltaE = q +w)

Arnav Saud 2C

qrev refers to the reversible reaction's heat while q refers to the overall heat

Arnav Saud 2C

Specific heat capacity can be described as the amount of energy (J, KJ, etc.) needed to raise the temperature of a given quantity by 1 degree.
I think the main thing you should do is to remember what values are needed being J/KJ over a temperature degrees (C,K,etc.) and a mass value in g,kg,etc.

Arnav Saud 2C

I think the way a closed system works is that energy is able to leave/enter the system, but matter cannot.
In an isolated system neither matter nor energy can leave/enter, and in an open system, energy and matter can both leave/enter.

Arnav Saud 2C

Hey! so for this problem you use q=m*deltaH to find delta H. From the table you find the difference between initial and final mass then divide the mass difference by the molar mass of the molecule. The boiling point is used to find delta S using the equation delta S= delta H/ T. Don't forget to con...

Arnav Saud 2C

Hello, I'm little confused on what exactly this problem is asking us to do and what it wants us to do with the table? Would it be possible for anyone to explain to me how were supposed to use it?
Thank you!

Arnav Saud 2C

Aside from doing practice problems, something you could try to do is figure out how the equations are related to each other. A lot of the equations are tied to each other in different ways, and if you can figure this out, it can help you improve your understanding for how you should use the equation...

Arnav Saud 2C

Bond energies that are taken for specific bonds like C-C are taken as an average of the energies of C-C bonds from a variety of different organic compounds. Since these specific bond energies are all averages, this makes them inaccurate, especially when you are adding up multiple bond energies toget...

Arnav Saud 2C

Vaporizing requires a far larger amount of energy compared to melting ice because there are more hydrogen bonds that need to broken in liquid water when you compare it to ice.

Arnav Saud 2C

Yes, if they don't give us temperature, assume that it is at 25 degrees celsius.

Arnav Saud 2C

Basically, you just make the pka value negative. Then you make the log and the pka to the power of 10. This should cancel out the log and you will get the ka value.

Arnav Saud 2C

Work can't be a state function because it's proportional to the distance an object moves. This means it depends on the path used to go from the initial to the final state.

Arnav Saud 2C

If I'm correct, the reason why we can add pka and pkb to get pkw is because pka and pkb are found by taking the logmarithm of the ka and kb. When you multiply two logs together, you can add their inner parts up.
Thus,
-log(ka*kb)) = -log(ka) + -log(kb) ---> This should translate to pka + pkb

Arnav Saud 2C

Hess's law basically describes that enthalpy is a state value which means that you can just add and subtract the enthalpy values. You don't have to focus on how the pathways go.

Arnav Saud 2C

The best method is to memorize all of the strong acids and strong bases. Everything else is considered as a weak acid or base.

Arnav Saud 2C

If the K value is less than 1E-3, you can set the x values from the ICE tables to 0.

Arnav Saud 2C

The main thing you need to understand from the principle is how volume, pressure and temperature changes are applied to Le Chatelier's Principle. You primarily should know that if you increase temperature in an exergonic reaction, it means that reactants will be favored, and if you increase the temp...

Arnav Saud 2C

K is the general terminology used. Kc and Kp are the more specific forms.
Kp is typically used when you are given bars while Kc is used when you are given a molar concentration (mol L-1 or M).

Arnav Saud 2C

It's false because increasing the concentration of the products would mean that the reaction equilibrium would lead to the excess product being used to create more reactants in order to bring the system back to equilibrium.

Arnav Saud 2C

Convert Ka to Kb by dividing Kw by Kb (10 -14 /4.0x10 -8 ) since the reactive ClO - is the conjugate base of the HClO, which gets you Kb=2.5x10 -7 . You can use this Kb to create the equation Kb=[OH - ][HClO]/[ClO - ] (2.5x10 -7 =x 2 /0.040) by solving this equation you get [OH - ]=x=6.52x10 -5 . Y...

Arnav Saud 2C

When q=k, the reaction is at equilibrium.
If q is greater that k, it means that the reaction will produce more reactants.
If q is less than k, it means that the reaction will produce more products.

Arnav Saud 2C

For that part of the problem, you just have to put the products/reactants and then solve for kc.
In this case it would be [NO2]^2/[N2O4]. Just plug in the given values and you'll get the kc.

Arnav Saud 2C

Temperature changes would result in a change in K.

Arnav Saud 2C

I think that most of the time ICE boxes are only necessary for weak acids and bases.

Arnav Saud 2C

I personally like to double check which reactant or product is going to increase or decrease. Also, always mark/write down the information you know and what you don't/what you need to find out. This'll let you organize yourself and prevent confusion when doing the ICE box. Also, something I personal...

Arnav Saud 2C

Only include water when its gaseous. If it's liquid or solid, it shouldn't be included.

Arnav Saud 2C

A net ionic equation is used to simplify a complete ionic equation. In a net ionic equation, all of the spectator ions are removed, only leaving the chemical species that are involved in the reaction. I'm not entirely sure, but I think that you would most likely use the net ionic equation to simplif...

Arnav Saud 2C

If the problem is some time of comparison, they will most likely give you K, or give you values to allow you to solve for K.

Arnav Saud 2C

You should use kelvin.

Arnav Saud 2C

Jay Solanki 3A wrote:the K value of 53.3 should not have a square root attached to it. Removing this square root and solving the resulting quadratic equation should result in the correct answer. Hope this helps!

Why would you not take the square root of 53.3? Aren't you supposed to take the square root of both sides?

Arnav Saud 2C

I think it still applies to water molecules. Water molecules have two atoms being hydrogen around the central atom and 2 lone pairs. This makes its structure AX2E2 (x=atoms, e= lone pairs). I think for the structure of water, that is just the optimal way it is. The lone pairs repel each other and re...

Arnav Saud 2C

The difference in electro negativity between the carbon and oxygen is greater than it is between the sulfur and carbon

Arnav Saud 2C

It's basically the number of nodes/the shape.

Arnav Saud 2C

For the purposes of the class, I believe we need to understand that water has amphoteric properties, and the metalloids are amphoteric.

Arnav Saud 2C

I believe that you can recognize it by finding how many lewis base sites are present in the molecule (having multiple lone pair donating sites that are used to bond to a central atom). An example is EDTA, a hexadentate ligand, is an example of a polydentate ligand. EDTA has six donor atoms with elec...

Arnav Saud 2C

Acid rain is mainly caused by the introduction of high levels of CO2 and sulfuric compounds being released from the burning of fossil fuels.

Arnav Saud 2C

I believe its caused by the electron-electron repulsion of the extra electron that oxygen has. It weakens electron shielding which lowers its ionization energy.

Arnav Saud 2C

For the purposes of this class, the p block elements that have an expanded octet are P, S, and Cl. H, He, Li, Be, B, and Al can have an incomplete octet.

Arnav Saud 2C

Generally, you want to first look at the overall negative charge of the structure, because that is what the all the charges of all the molecules should add up to. Then identify what all the negative charged molecules, and the remaining charge will be the plus on the central molecule.

Arnav Saud 2C

I'm pretty sure its ferrate only for coordination compounds.

Arnav Saud 2C

Generally, try to find all the negative charged molecules/atoms. Then find all the positive charged molecules/atoms. Add up all the negative and positive charges together. The leftover negative charge should then be turned positive and that should be the charge. A simple example is Titanium(4) Dioxi...

Arnav Saud 2C

c will always be the constant for the speed of light(at least for this class).

Arnav Saud 2C

The main thing when looking at these kinds of molecules is to figure out what atoms are bonded to each other, and potential dipole moments. Generally, if a molecule is not asymmetric and the atoms bonded to the central atom are different, then the molecule is polar. An example of each is H2O with it...

Arnav Saud 2C

For problems like these, its best to memorize all of the strong bases (there are only a handful of them). Anything that is not of that list is not a strong base. If you had to compare KOH and Ca(OH)2, Ca(OH)2 is higher because it has an extra OH which makes it more alkaline or basic. A side note: ac...

Arnav Saud 2C

The main importance that he presented about acidic rain is the way acids can be circulated through the earth's atmosphere. He was also explaining the impact of acid rain on biological system and on how its formed.

Arnav Saud 2C

The general trend of the hydrohalic acids (HCl, HBr, HI) is that HCl is stronger than HBr and HI is stronger than HBr. These 3 acids are all classified as strong as well. Why is HF not classified as a strong acid? What property of HF causes it to not completely dissociate in solution(be classified a...

Arnav Saud 2C

You should try to memorize all of them with a greater focus on the more common ones because generally if you know all the common ones, you can cross those out in a multiple choice test. Then you can try to recognize them based on their names because a lot of the VSEPR structures are quite recognizab...

Arnav Saud 2C

For this class, I go to the UA sessions a lot more than I did from the start of the quarter. Additionally, I have a bigger emphasis on textbook problems for practice as well, and I combine this with spaced out readings of the chapters preceding an exam. Then, I do a review of everything in the days ...

Arnav Saud 2C

If I'm correct, for this class, the main incomplete octet elements you need to know are Be, B, and Al. The textbook section 2C.3 has a good explanation on the incomplete octet elements as well.

Arnav Saud 2C

Single bonds only have sigma bonds while double bonds have one sigma and one pi bond. A triple bond has 1 sigma bond and 2 pi bonds. Sigma bonds allow for flexibility of a molecule, which, as seen Dr. Lavelle's lecture with his marker demonstration, allows for the structure to bend without breaking....

Arnav Saud 2C

You can tell if something is ionic or covalent with a variety of ways. The main way is to use your periodic table and know the electronegativity trends. The greater the distance between two elements in a bond, the more likely the bond is going to be ionic/polar. Additionally, when drawing lewis stru...

Arnav Saud 2C

The main reason why this occurs is because there are only 4 regions of electron density. The double bond does not count as an extra region, which is why there are only 4.

Arnav Saud 2C

GC is stronger than AT because it has one extra h bond.

Arnav Saud 2C

Yes, it has 3 h-bond pairs when its with cytosine.

Arnav Saud 2C

Yes, I'm pretty sure that the overall energy of resonance hybrids is lower because they are more stable.

Arnav Saud 2C

The unit is known as millimole, which is 10^-3 of a mol.

Arnav Saud 2C

https://secureservercdn.net/45.40.146.2 ... /K5EcA.jpg
This link should have some pictures so you can see a visual representation.

Arnav Saud 2C

Shape is a good indicator of whether or not something is polar/nonpolar; however, you also need to check the dipole moments as well.

Arnav Saud 2C

London forces are in all bonds; however, they are the only type of bonding present in most if not all nonpolar bonds.

Arnav Saud 2C

They're experimentally determined, and generally for usage in class, I think we just need to know the bond angles for the generalized shapes, and then make a prediction on what it'll be based on the general shapes.

Arnav Saud 2C

As a molecule becomes more positive in charge (a cation), it becomes smaller. I think this is because the repulsion between electrons is weaker and the strength of the effective nuclear charge from the nucleus is able to pull them closer. As a molecule becomes more negative in charge (an anion), it ...

Arnav Saud 2C

I think concerning shape and structure we'll have to memorize all the types and how to determine them when looking at a lewis structure or VSEPR notation.

Arnav Saud 2C

I don't think we'll need to calculate bond length for this midterm.

Arnav Saud 2C

N, O and F are all small and highly electronegative. This can be seen through the trends on the periodic table.

Arnav Saud 2C

The answer is false because you have to increase the frequency in order to increase the energy of the photons. Increasing the intensity means that the number of photons that are emitted is increase.

Arnav Saud 2C

The goal on formal charges is maximizing the number of atoms in a molecule with 0, and to get positive charges on the least electronegative atoms in the structure and negative chares on the most electronegative atoms.

Arnav Saud 2C

A radical is a species with an unpaired electron. This lone electron makes the species incredibly reactive.

Arnav Saud 2C

ms refers to the directions of the spin. +1/2 is up spin and -1/2 is down spin. A problem would probably give us n=2, l=0, ml=0, ms = +1/2. The answer would be 2s, and it would have one electron with an up spin.

Arnav Saud 2C

Can someone explain that in other words? I know that the bigger the molecule the stronger the forces, but for some reason that still isn't making sense to me. I would have thought that because the valence electrons are further from the nucleus the forces would be weaker, but I know that is not the ...

Arnav Saud 2C

The main thing is that compared to spherical molecules, rod shaped molecules have a greater amount of surface area for the electrons of the molecule to interact in.

Arnav Saud 2C

Some resonance structures are more stable because their formal charges are minimized. The more charges in the structure that equal zero, the more stable it is. Additionally, the placement of negative and positive charges also differs between different resonance structures. Negative formal charges on...

Arnav Saud 2C

London Dispersion Forces(LDF) only exist in nonpolar molecules. CH4 is a nonpolar molecule which causes LDF to exist between the bonds of CH4. Concerning CH4, you know it is nonpolar because the lewis structure shows 4 hydrogens surrounding a carbon. Because they are all the same molecule, their dip...

Arnav Saud 2C

Chem_Mod wrote:Correct.
I will go through this in my 3pm discussion section today.

ok thank you!

Arnav Saud 2C

At around the 39 minute mark of today's lecture, Dr. Lavelle was talking about the Na+ and Cl- relationship and the energy they output. Just wanted to confirm, does a negative value (Ex. -250 Kj.mol) means that energy is being released, and a positive value (Ex. +250Kj.mol) means that energy is bein...

Arnav Saud 2C

One of the easiest ways is to go to the quick links section at the top left near FAQ. Hitting it will open a drop down with a couple of different links with one of them being your posts.

Arnav Saud 2C

Personally, I like to use the textbook for my problems, etc; however, if I dont understand a concept or I need help on something, I normally attend a drop in session.

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