CHEMISTRY COMMUNITY

Ethan Yi 1K

yeah it wasnt on the equ sheet

Ethan Yi 1K

yeah. the equations sheets tell you this.

Ethan Yi 1K

its more theoretical for a lab situation. we dont have any calculations with this i dont think

Ethan Yi 1K

there will be more of the recent section compared to older ones since we have not been tested on the new topics yet. But study everything.

Ethan Yi 1K

the order of a reaction depends on how the concentrations of reactants affect the rate of the reaction. if the reactant concentration does not impact the rate, it is zero order (rate = k). if there is a linear relationship, where the rate and concentration have a direct correlation, it is first orde...

Ethan Yi 1K

the anode half reaction and cathode half reaction are separated by the double line which represents a salt bridge

Ethan Yi 1K

see if there are standard conditions being used

Ethan Yi 1K

id guess during our next discussion

Ethan Yi 1K

M is equal to mol/L so both are the same

Ethan Yi 1K

n is the change in moles of the reaction so you can look at the two sides of the reaction and see the difference

Ethan Yi 1K

these are all related through different equations that are given to us. they are all significant in their own way, as G tells us about spontaneity, and H tells us about endothermic/exothermic.

Ethan Yi 1K

if T is 0 it is at absolute zero, which is impossible, and so yes, T has to be greater than 0K.

Ethan Yi 1K

its not that gibbs free energy is negative or positive, but the change in Gibbs tells us if the reaction is spontaneous is not. negative delta G is spontaneous.

Ethan Yi 1K

for hess's law, if you flip an equation, you change the sign. If you double the contents of a reaction, you double the deltaH value

Ethan Yi 1K

W = (# of equal energy conformations)^(# of molecules)

Ethan Yi 1K

you should look at the states then the size of the molecules. g > l > s and heavier/more atoms > lighter/less atoms

Ethan Yi 1K

Eruchi Okpara 2E wrote:So how do we know when to use either 3/2R or 5/2R?

as stated above, use Cv = 3/2 R at constant volume and use Cp = 5/2 R at constant pressure

Ethan Yi 1K

MadelineHlobik wrote:In an isolated system, no energy or matter leave the system right? However in a closed system energy can leave the system?

yes, in a closed system, energy can enter and leave freely.

Ethan Yi 1K

aaronharouni wrote:How do you know which method to use when dealing with bond enthalpies?

draw the lewis structures

Ethan Yi 1K

steam has a lot more energy already put into it that made it go from water to steam, which is why it causes worse burns

Ethan Yi 1K

look at what units your other values are in and use the R that will allow the units to cancel out.

Ethan Yi 1K

it says that the total entropy of an isolated system is always increasing. Basically, the more that energy is transformed, the more energy is wasted.

Ethan Yi 1K

the 2NO's are on opposite sides of the equation and therefore will cancel out. however, the O2's are on the same side, so you add them together.

Ethan Yi 1K

that energy is being used to break bonds

Ethan Yi 1K

you have to put in energy in order to break bonds. when bonds form, they go to a more stable state so energy is released

Ethan Yi 1K

yeah. if your estimate is <5% of the original value, then the estimate is ok to use. and the range is 10^-3 to 10^3

Ethan Yi 1K

for both Q and K, the products are in the numerator and thus if Q>K, there is an excess of products, and the reaction will proceed in the reverse reaction. likewise, the opposite is true of Q<K

Ethan Yi 1K

Kp is p for partial pressures (gases) and Kc is c for concentration

Ethan Yi 1K

K is the [products]/[reactants] at equilibrium. Q can be used anytime during the reaction. For instance, at the very start of the reaction, there may be a lot more reactants than products, and at this point, [products]/[reactants] would be Q, not K bc the reaction is not at equilibrium yet.

Ethan Yi 1K

you have to get the net ionic equation and then use that to find K. Also, solids and liquids are not included in K.

Ethan Yi 1K

K is the value at equilibrium, while Q is the value or [products]/[reactants] anytime during the reaction.
if K=Q, the reaction is at equilibrium
if K>Q, then [reactants]>[products] and the forward reaction is favored
if K<Q, then [reactants]<[products] and the reverse reaction is favored

Ethan Yi 1K

it is easily ionized

Ethan Yi 1K

for ml to be -9, the l value must be at least 9 and the n must be at least 10 which does not exist and it purely theoretical

Ethan Yi 1K

smaller and highly charged are stronger

Ethan Yi 1K

if you draw out the lewis structure, you can see if there is a lone pair which would allow a molecule to act as a base, or the opposite for an acid where you can see if there is room for another pair

Ethan Yi 1K

marg44 wrote:For these sigma and pi bonds, is one bond stronger than the other? Or are they of equal strength?

i think a sigma bond alone is stronger than a pi bond would be alone, but a pi bond is never alone, it's always on top of a sigma bond

Ethan Yi 1K

probably both

Ethan Yi 1K

the pi bond will break first because it is weaker than the sigma bond (less overlap).
a double bond is stronger than a single bond because it has a sigma AND pi bond rather than just a sigma bond.

Ethan Yi 1K

so is the test only on the things we learned after the last midterm?

Ethan Yi 1K

yeah youre right but <109.5 is still around so the answer key is correct. but in the future for the class we should use <109.5 im pretty sure

Ethan Yi 1K

not every molecule has a permanent dipole, but they do have temporary ones like van der waals forces

Ethan Yi 1K

yeah pretty much. down the group, polarizing power decreases. its the opposite for polarizability

Ethan Yi 1K

the lone pair of electrons has a negative charge that will repel the bonding pairs that also have a negative charge, changing the shape.

Ethan Yi 1K

^ the lone pair on the central atom creates a repulsive force on the bonding pairs

Ethan Yi 1K

if there are no lone pairs, then the molecule should follow the pattern of being either linear, trigonal planar, or tetrahedral, depending on the number of bonds. if lone pairs are present, the molecule will be bent because the bonding paris will feel repulsion

Ethan Yi 1K

just look and see if there are any lone pairs. If there are, there will be repulsion with the bonding pairs and thus a bent shape will be formed.

Ethan Yi 1K

you should calculate the formal charge on each atom and see what bond arrangement gives you a formal charge of 0 on most or all of the atoms.

Ethan Yi 1K

The extra electrons go into the d orbital of the atom. Thats why only elements in rows 3 or higher can have expanded octets, since they have a d orbital.

Ethan Yi 1K

And the elements in rows 3+ can have expanded octets because they have a d orbital that the electrons can fill

Ethan Yi 1K

He said in class that it would be obvious if a wavelength could be measured or not. He said he wouldn't make the answer something that could be ambiguous and go either direction, so dont worry too much.

Ethan Yi 1K

Ag is one of the exceptions where the 4d orbital will actually take an e- from the 5s. therefore, the ground state of Ag would be [Kr]4d^10 5s^1. Because in this case Ag is an ion in the form Ag^+, we remove an electron from the 5s orbital, leaving [Kr]4d^10.

Ethan Yi 1K

Yes. Ionic bonds are formed when two atoms have electronegativities that are not close to each other, so that an atom pulls an electron off of another atom. This means two nonmetals do not form ionic bonds because their electronegativities are too close together, as they form covalent bonds instead.

Ethan Yi 1K

It's easier for Li and Be to become stable by losing 1 or 2 electrons respectively and becoming like the noble gas He, rather than gaining 6 or 7 electrons to become like Neon.

Ethan Yi 1K

Just to reiterate, when the energy difference is smaller, wavelength is larger, and frequency is lower.

Ethan Yi 1K

its actually not the same symbol. velocity is the actual letter 'v' but frequency is the Greek letter nu. It's like a curvy v.

Ethan Yi 1K

its saying that the (indeterminacy in position) x (indeterminacy in momentum) >= h/4pi. its always going to be >= because its saying those two factors multiplied will be, at a minimum, h/4pi. Its possible for both position and momentum to be very indeterminate (a large number), but it is not possibl...

Ethan Yi 1K

And also, for substances like caffeine that are made up of more than just H,C, and O, there would just be an extra product. in the case of caffeine, because N is in its structure, NO2 would be on the products side to account for this.

Ethan Yi 1K

No, even though it says SO3 molecules, it still wants you to find the number of moles. The question wants you to treat the molecule as a whole, and find the number of moles of the molecule. In part a you find the number of moles of an ion, and likewise in part b you find the number of moles of a mol...

Ethan Yi 1K

Yeah to chain off of what the others said, you should start by balancing any of the elements that only appear once on each side of the process. In this case, that would be nitrogen. From there, balance either C or H because they appear the next least (Oxygen should be last because it appears the mos...

Ethan Yi 1K

On the test, the questions will most likely specify what units they want the answer in. And if they tell you to to find for example "mass" without units, I assume we should use the base SI units?

Ethan Yi 1K

Go to Dr. lavelle's website and click on the syllabus. All of the homework should be listed there, separated by topic. Here's the url https://lavelle.chem.ucla.edu/wp-conten ... SYLL_1.pdf

Ethan Yi 1K

the molecular formula will be an exact multiple of the empirical. So the molar mass of the molecular formula divided by the molar mass of the empirical should turn out to be a whole number.

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