CHEMISTRY COMMUNITY

Jaden Joodi 3J

While it might have panned out this way for this question, it is possible to have two of the same concentrations of [C] that is meant to show that one of the other reactants is is affecting the initial rate.

Jaden Joodi 3J

Given a formula alone, it is impossible to determine the order of reactants. You must be given a table complete with experiments that allow you to see see what increasing the concentration of only one of reactants does to the amount of product.

Jaden Joodi 3J

This equation can only be used when work is an irreversible expansion (constant external pressure)

Jaden Joodi 3J

The catalyst does not change the amount of heat absorbed or given off for a reaction. It only lowers the activation energy required to activate the reaction

Jaden Joodi 3J

Always use the R value that cancels outs the variables in whatever equation you are using.

Jaden Joodi 3J

As several people have already stated, the crash course videos are entertaining and have a relatively good amount of information. For easy to read written texts I would recommend chemistry libre texts.

Jaden Joodi 3J

n in this case refers to the moles of electrons transferred in the reaction
i.e for a reaction where irons the oxidation is like this: Fe----> Fe^+3
The moles of the electrons transferred would be 3

Jaden Joodi 3J

The salt bridge prevents the charges from being too stacked on one side causing the reaction to stop

Jaden Joodi 3J

Because electrons always flow from the anode to the cathode, the species losing electrons (oxidized) is the anode and the species gaining electrons (reduced) is the cathode

Jaden Joodi 3J

As long as the units cancel, and you convert to whatever the answer is looking for, it should always work!

Jaden Joodi 3J

While n is moles of electrons, the usage of it in this formula, when given a redox reaction, is simply the number of electrons transferred.

Jaden Joodi 3J

The ln should be able to always be used. The log one can only be used when the temperature is 25C (298.15 Kelvin)

Jaden Joodi 3J

I think that in this formula, n actually represents the number of electrons transferred, but I am not entirely sure about that

Jaden Joodi 3J

E naught is the energy under standard conditions, whereas E is just the general energy. In order to find the energy not under standard conditions, you must use E naught

Jaden Joodi 3J

As a rule of thumb, always put phases unless it specifically tells you that you do not have to use phases.

Jaden Joodi 3J

Most of the time it gives you phases, but I think for when it does not, you just have to use common sense in regards to the reaction. For instance, H2O is most likely to be liquid in a redox reaction.

Jaden Joodi 3J

Because the function for work is looking at work done from the perspective of the system. To the system, it is losing its ability to do work, by doing work.

Jaden Joodi 3J

I think that the only important abstraction to be gained from knowing that something is a state property, is that it's change in value is always equal to final minus initial.

Jaden Joodi 3J

Most have already mentioned that H° is H at standard conditions, but I just wanted to add that I think Dr. Lavelle mentioned that whenever we see the ° symbol, that it always means standard conditions.

Jaden Joodi 3J

If Q<K, there are more reactants than products. This means that more reactants will become products in order to reach equilibrium. The opposite is also true. If Q > K, there are more products than reactants. This means that more products will become reactants in order to reach equilibrium. If Q=K, t...

Jaden Joodi 3J

Just use whichever R value will cancel out the other units in the equation, so that the only units remaining will be those needed for the answer.

Jaden Joodi 3J

As people have said, d represents the derivative. What's more important to know are the equations that Lavelle derives from these.

Jaden Joodi 3J

From what I remember, when using the first law of thermodynamics, we treat open systems as being closed.

Jaden Joodi 3J

From the math point of view, the reason that ΔH plays such a large role at low temperatures is because it is being divided by temperature. The difference between being divided by 1, 2, 3 is quite large compared to being divided by 50,51, 52.

Jaden Joodi 3J

In question #4, n is still taken into account. Because we are asked to calculate PER MOLE, we just use 1 for n.

Jaden Joodi 3J

Theoretically, you could change the R value, but it would be much easier to convert kPa to atm(1 kPa = 0.00986923 atms)

Jaden Joodi 3J

The first step is to take the grams of NaN3, and turn it into moles. Then, you use the given equation to convert the moles of NaN3 into moles of N2(since it is the only gas). Now, you want to use PV=nRT to find the volume. Once you find the volume, use the formula w= -p*deltaV. This will give you th...

Jaden Joodi 3J

I am a little confused on your question? Every sapling specifies whether it wants the answer to be in Joules or L*atm.

Jaden Joodi 3J

It depends on what constants you are using in your calculations. If you are using any constant of R in your calculation, you must convert the Celsius to kelvin.

Jaden Joodi 3J

I'm pretty sure a vapor and a gas are the same thing? After doing a little google search, it seems like there could be a difference. It seems that a vapor is a mixture of a gas and a liquid, where the gas is the main composition.

Jaden Joodi 3J

Cp = Cv + R
(The R used in this is 8.31446261815324)
For more information check this nasa sheet:
https://www.grc.nasa.gov/www/BGH/speche ... iven%20gas.

Jaden Joodi 3J

Intensive properties are properties that do not change depending on the amount of substance. e.g mass and volume
Extensive properties do change depending on the amount of substance. e.g density and color

Jaden Joodi 3J

Would everything be a perfect system, or is a perfect system only possible in theory?

Jaden Joodi 3J

In lecture, Dr. Lavelle said that molar heat capacity was less used than the specific heat capacity, but I do believe that it is used when heating a gas at a constant pressure.

Jaden Joodi 3J

Because a closed system disallows matter from being exchanged, it is impossible for the volume in the system to change.

Jaden Joodi 3J

As a follow-up question, if isolated systems are so boring, why are bomb calorimeters so widely used?

Jaden Joodi 3J

pKa is -log pKa

Jaden Joodi 3J

It just depends on what way the reaction is going. If it is going away from the products and towards the reactants, it will be -x and +x respectively. (and vice-versa)

Jaden Joodi 3J

After reading this thread I am a little confused. What does it mean to approximate x as 0? Could you do this on any of the homework problems? I solved all of them with the quadratic equation. How would you do it the other way?

Jaden Joodi 3J

I see people saying that we can assume this when Ka is less that 10^-3. Doesn't this mean that for problem 1 on the sapling, we could have assumed that x was 0? For this one I just used the quadratic formula?

Jaden Joodi 3J

I don't know which problem it is, but during the saplings, the discriminate should never be negative. You most likely dropped a negative somewhere or just made a general calculation error.

Jaden Joodi 3J

The easiest way to do this is to look at what is being added to the reaction. If more of the product is being added to the reaction, you will subtract x from the products.

Jaden Joodi 3J

Q is simply the concentrations of the molecules at any given time. It can be, but is not necessarily, equal to Q. Given enough time, Q should always reach K

Jaden Joodi 3J

For endothermic reactions, K increases when temperature increases
For exothermic reactions, K decreases when temperature increases.

Jaden Joodi 3J

As many others have said, look at which one donates protons and which one accepts protons. There isn't a real way to determine if it is a strong acid/base except for just memorizing the lists of them.

Jaden Joodi 3J

Yes, you want to test both positive values in order to see which one would fit in the ICE table

Jaden Joodi 3J

You use the value of R that would cancel out the units of the pressure, volume, and temperature.

Jaden Joodi 3J

As a follow-up question, if real and ideal gasses are so different than each other, why is it helpful to treat real gasses the same as ideal gasses? Would this assumption not cause problems?

Jaden Joodi 3J

I did a little research and it would appear that the only way a reaction could not reach equilibrium, would be if the K value was incredibly small or incredibly large. For example, if the K value was something like K = 10^30, it would mean that there would be 10^30 molecules of the product for every...

Jaden Joodi 3J

If we are assuming that 1 bar is equal to 1 atm, would we assume that the conversion would allow for infinite sig. figs?

Jaden Joodi 3J

Does anybody mind posting an example of a reaction involving water, in which H2O would be included in the ICE table?

Jaden Joodi 3J

In this situation, the acid will not dissociate, so the solution will remain neutral

Jaden Joodi 3J

Yes, please make sure you know the bond angles. Here is a good reference image:
https://i.pinimg.com/originals/62/14/b5 ... 4ee088.jpg

Jaden Joodi 3J

I think that the only polyprotic acids we need to know are:
H2SO4, H2CO3, and H3PO4

Jaden Joodi 3J

I don't really know how to figure out if a substance is amphoteric, but, I think that the only ones we need to know are:
BeO, Al2O3, Ga2O3, SaO2, Sb2O5, and PbO2.

Jaden Joodi 3J

Electron Geometry treats electron pairs as if they are bonded atoms.
i.e The electron geometry is the same for a molecule with the structure AX2E2 as it is for AX4

Jaden Joodi 3J

In order to go from pH to H+, you would take the inverse log of the negative pH.
i.e 8.85 = -log(x) and solve for x

Jaden Joodi 3J

Coordination number is simply the number of the bonds connected to the transition metal cation.

Jaden Joodi 3J

c is always the speed of light as long as it is in a vacuum. If it is the speed of light not it a vacuum, then it varies.

Jaden Joodi 3J

I see people mentioning that planar shapes would never be ideal for 6 bond, because the electrons want to be as spread out from each other as possible. What number of bonds would be fine being in a planar shape?

Jaden Joodi 3J

A coordinate covalent bond is specifically when a transition metal cation bonds with anything that can donate electrons (these are called ligands).

Jaden Joodi 3J

They are more stable due to the delocalization of electrons. The energy of delocalized electrons is spread out over a larger area, making it more stable.

Jaden Joodi 3J

Because of the way lone pairs interact, the lone pairs would be closer to each other, while pushing away the two bonded atoms. Keep in mind that a square planar formation requires 4 bonded atoms and two lone pairs.

Jaden Joodi 3J

https://i.pinimg.com/originals/62/14/b5 ... 4ee088.jpg
This chart has almost if not every single molecule shape with drawings and bond angles.

Jaden Joodi 3J

The easiest way to know the bond angle is simply by memorizing it for each shape. I would recommend looking up tables that have all of the possible molecular geometries, and their corresponding bond angles

Jaden Joodi 3J

As to your first question, you bring up a really good point. I initially drew it all out linearly with double bonds connecting all the carbon atoms, and based on one of the questions that follow asking about the bonds connecting the carbon atoms it is clear that they would like us to draw it all wi...

Jaden Joodi 3J

Looking at the the lewis strucutre, it would appear C2H4 is indeed two trigonal planars.

Jaden Joodi 3J

The general guideline for hybridization is as follows: Regions of e- density = number of hybrid orbitals 1 s-orbital + 1 p-orbital → 2 sp hybridized orbitals (Linear) 1 s-orbital + 2 p-orbitals → 3 sp2 hybridized orbitals (Trigonal planar) 1 s-orbital + 3 p-orbitals → 4 sp3 hybridized orbitals (Tetr...

Jaden Joodi 3J

The way I learned the bond angles in high school, was by making a table that contained the names of molecules, drawings of them, and the bond angles. By studying this, it allowed me to later recall the drawing that contained the bond angles

Jaden Joodi 3J

After drawing the lewis dot structure, there is an unfilled octet, then it is a lewis acid. If there is a lone pair, it is a lewis base.

Jaden Joodi 3J

I do not believe that we are expected to calculate bond length. BUT, it is important to know trends for bond length. Know that bond length is inversely proportional to bond strength. Also make sure to remember that the larger an atom is, the larger the bond length will be.

Jaden Joodi 3J

LDF should be present in all molecules, polar and non-polar. This is because LDF are a sort of pure chance thing, where electrons just end up on one side of a molecule more than the other

Jaden Joodi 3J

Sulfur and Chlorine are the only two exceptions I believed you did not mention. Like Phosphorus, these are able to accommodate more than 8 valence e-. This is due to the 3d block being able to be used to store extra electrons

Jaden Joodi 3J

For a rod shaped model, the two molecules are much closer together, sharing a much greater surface area. With this, electrons are much closer together, making dipole moments all the more common.

Jaden Joodi 3J

From what I understand there are no exceptions. Hydrogen bonding can occur when ONLY N, O, and F are present. If they are not present, there can not be hydrogen bonding

Jaden Joodi 3J

Is Chem_Mod Dr. Lavelle? Or is it a shared account between Lavelle and TA's? Anyways thanks for the info!

Jaden Joodi 3J

I see others explaining the two concepts thoroughly, so I will just hijack this thread in order to share a little tip for remembering Hund's rule from my old chem teacher. Hund's is for heaven. What she meant by this is that, electrons fill up separate orbitals in the same subshell, with parallel sp...

Jaden Joodi 3J

From what I understand, London dispersion forces are when, through random chance, electrons end up being on one side of the compound more than the other. This causes one end of the compound to be more negative, while the other end is more positive.

Jaden Joodi 3J

As a follow-up question, do we know how much material is covered/when midterm 2 is?

Jaden Joodi 3J

After reading some on the replies, I would like to ask the follow-up question: How can we know if a compound receives its needed electrons solely from another compound?

Jaden Joodi 3J

So far I have kept my head above the water, but man this quarter is a ton of work. It feels like the only thing I do is work all day. But besides that, Chemistry class itself is going pretty well!

Jaden Joodi 3J

^^^^^
The reason why the effect going across a row has such a lower effect on the decrease of the atomic radii is because of the electron shielding's limited effect. Increasing radii through gaining new shells is much greater of an effect.

Jaden Joodi 3J

You would only assume this if the it was an emission spectrum problem. If it was an absorption problem, you would assume that n=1 is the initial.

Jaden Joodi 3J

Happy Halloween Everybody!!!
I thought it would be fun if everybody listed the things they were doing/did for Halloween. I dressed up with some siblings and watched the ring. We also ordered some sushi. What has everyone else done for Halloween?

Jaden Joodi 3J

As a good rule of thumb, it is best to put the atom that has the least electronegativity in the center.

Jaden Joodi 3J

I was wondering the same thing but, for now I would say to just try and get it done before then

Jaden Joodi 3J

To try and recommend shows with scientific themes, Dr. Stone is a great show involving someone trying to rebuild society with science. There are numerous occasions in the show where the main character uses accurate chemistry in order to accomplish this. I highly recommend this show.

Jaden Joodi 3J

The questions appeared to be in the correct order when I completed them a few nights ago.

Jaden Joodi 3J

I am fairly certain that the only things you are allowed to have are the periodic table and the approved list of formulas, both of which can be found on Lavelle's website.

Jaden Joodi 3J

To add on to what everyone else is saying, you know that n=1 is involved if it is a hydrogen atom emitting/absorbing UV rays. N=2 is involved if it is in the visible light spectrum.

Jaden Joodi 3J

From what I understood from my TA, the only thing that is graded is the test itself. Because of this, we can assume that no work needs to be shown. (I would definitely recommend you write the work down though, as it is easy to get lost in the problem without it.)

Jaden Joodi 3J

Whenever I am feeling stressed out from class, I normally relax with a nice cup of coffee and a snack. No matter how stressed I was before, this always helps me chill out for at least a few minutes.

Jaden Joodi 3J

I am fairly certain that there is no relationship between the frequency/wavelength of electromagnetic radiation, and the speed at which it moves. This is because electromagnetic radiation moves at a constant speed of 3.0 x 10^8 m/s in a vacuum. This is how we get the formula c= wavelength * frequency.

Jaden Joodi 3J

To add on to what everyone else in the thread has already stated, planck's constant is used to relate the frequency of a wave to the energy of a photon. It was calculated by measuring the relationship between the two. It turned out that the frequency and the energy of the photon were directly propor...

Jaden Joodi 3J

DanielHong2L wrote:If I remember correctly, according to my TA and other folks, TI 84's can be used during exams.

Nice! Thanks for the quick response. I will update this thread later if I get confirmation from my own TA.

Jaden Joodi 3J

I will try and give a decent explanation on how to solve this problem. The first step of is to analyze exactly what electromagnetic waves this college student would be running in to throughout the day. When reading, the student encounters visible light waves When at the dentist, X-rays When microwav...

Jaden Joodi 3J

My strategy has been to watch lecture and take notes. Afterwards, I watch the audio-visual focus topics and take the post assessments. If I feel like I need some more practice, I try and do some of the recommended book problems

Jaden Joodi 3J

On that note, does threshold energy refer to the amount of energy needed to move the electron in general or does it differ depending on the level level? All the threshold energy refers to is the energy required to dislocate an electron from an atom of any metal. If the energy of the photon was the ...

Jaden Joodi 3J

It seems that we are unable to use calculators that can use text. This would lead me to believe that I could not use my handy dandy TI-84 calculator. Anybody have any ideas on some chemistry approved calculators?

Jaden Joodi 3J

It is very clear that everyone in this thread would love for the music to return; I would agree. In the event that the music does not return, I would love to know if anybody knows the name of this amazing track. I would love to listen to it before every lecture, just so I can get hyped to learn some...

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