CHEMISTRY COMMUNITY

kendal mccarthy

I am just going to put together a comprehensive study guide with a ton of example problems from outlines 1-6.

kendal mccarthy

My chem 14BL class made the final a gradescope exam so we have to print it out, complete it, and then turn it into gradescope within the open and close date of the test. I have heard a couple other chem profs are doing a similar type of thing but we will see.

kendal mccarthy

Thank you for posting this Dr. Lavelle!

kendal mccarthy

I am assuming this means any resources we have access to we can use for this final. I am not sure how this would work yet as we don't know the window we can turn in the test but we will see when Lavelle lets us know :)

kendal mccarthy

My TA sent us an email and told us to send him a picture of our HW. He also told us to make sure to put our name and section as it will be easier to grade.

kendal mccarthy

Grades are avaliable for viewing on MyUCLA. Also my TA said he would come up with a plan so we would be able to get them back before the final.

kendal mccarthy

Possibly take home or online final or maybe smaller rooms for the final exam to be given? My other classes have been changed to online exams or to turnitin.com assignments.

kendal mccarthy

Yes, just shoot your TA an email with a picture of the homework to be safe. Mine emailed a couple hours ago telling us to do that.

kendal mccarthy

Hi! I was wondering if anyone has heard anything about what the Chem department might do about finals from friends taking other chem related exams. Also, if the format of the test will be different due to it possibly being take home, will the final exam review sessions (if we are able to have any) c...

kendal mccarthy

well because all classes including discussion sections are not allowed possibly review sessions will be bruincast? And about the final, no idea, I hope we can still get partial credit for work though somehow haha.

kendal mccarthy

This is because the Evalue at the cathode basically determines if the Ecell will be positive or negative. When the value is positive the system can do work, when the value is negative work must be done on the system. The equation is Ecell=Ecath-Eannode, so if Ecath>Eanode, the equation will have a n...

kendal mccarthy

I think most combustion reactions are spontaneous because they are exothermic, releasing heat, and usually cause an increase in gaseous substances, which have a higher value for entropy. It really depends on other determining factors, however.

kendal mccarthy

yes, n is referring to the number of electrons transferred in the redox reactions involved at the anode and cathode.

kendal mccarthy

Yes, if the potentials are not given you can assume the cathode is on the right and the anode is on the left.

kendal mccarthy

You balance the redox reactions, and the least common denominator of electrons transfered on the product and reactant side is equivilant to n.

kendal mccarthy

awesome congrats :)

kendal mccarthy

yes, you must balance both half-reactions to see if the electrons exchanged is the same, and if not multiply by a coefficient so they cancel out when they are added together to create the full balanced reaction. This value that cancels is your n.

kendal mccarthy

yes, we will most likely be given either a sheet with the cell potentials or they will be given on the problem if need be.

kendal mccarthy

without the salt bridge, the charges would build up disabling the flow of electrons due to uneven charges between the two half cells of the voltaic cell. The salt bridge monitors the charges on each side, allowing electrons to continue to flow from the anode to the cathode without a buildup of posit...

kendal mccarthy

The entirety of outline 5, which is electrochem, and the second page of outline 4. Do the HW probs on the outlines I think that is the best form of preparation :)

kendal mccarthy

Write the half reactions and balanced equation for the cell reaction.

I am not sure how to do this for part (d) which gives
Pt|O2|H+||OH-|O2|Pt

I don't understand how to get the half-reactions for either side.

kendal mccarthy

If you're not part of the solution, you're part of the precipitate.

kendal mccarthy

I keep laughing at the jokes on here cuz they are all sodium funny !!!

kendal mccarthy

It was moved to week 9. So during your discussion section, the test will be given.

kendal mccarthy

Based on your given values, then you can determine which value to use. 8.314 J·K-1·mol-1 or 0.0821 L·atm·K-1·mol-1 can be used to cancel out units and obtain a value.

kendal mccarthy

I think for neutral solutions mainly one should use h2o to make up the difference in redox reactions.

kendal mccarthy

Test 2 will be based on material after the midterm. Since much of the midterm was acid-base and equilibria, however, I would also study some thermochemistry and thermodynamics just in case.

kendal mccarthy

I think he will curve the class to the median which is a B.

kendal mccarthy

STP is just 273.15K and 1 atm. These values are mainly just for theoretical calculations because 0K is not feasible in everyday life.

kendal mccarthy

DeltaS total= DeltaS system + DeltaS surroundings

And temperature does help determine if a reaction is spontaneous. Using the formula deltaG=deltaH - TdeltaH you can see if a reaction will be spontaneous or not depending on T.

kendal mccarthy

Treat heat as another product or reactant. When I know a reaction is exothermic I write heat on the product side, as exothermic releases heat. If I know a reaction is endothermic I write heat on the reactant side. Then treat heat as you would a product or reactant. ex. if a reaction has an increase ...

kendal mccarthy

entropy is equal to S. DeltaS is the change in entropy. If the reaction is reversible, the total deltaS, which is equal to the deltaS of the system + the deltaS of the surroundings, is equal to 0.

kendal mccarthy

haha omg I just wrote down 25 instead of 22.5 ok that makes sense now

kendal mccarthy

"A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45°C to 23.97°C. What is the heat capacity of the calorimeter?" I set up this problem doing qcal=Cc...

kendal mccarthy

I was having trouble with this one too. I think the Cu final should be the same as the Water final.
The setup should be:
20*0.39*(T-100) = 50.7*4.18*(T-22)

instead of 20*0.39*(100-T) = 50.7*4.18*(T-22)

kendal mccarthy

a closed system can transfer energy to the surroundings but not matter. an isolated system can not transfer energy or matter to the surroundings. an example of a closed system would be an ice pack. an example of an isolated system would be a thermos.

kendal mccarthy

"A piece of copper of mass 20.0 g at 100.0 C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings." I am unsure how to calculate the final temp of the wa...

kendal mccarthy

Can someone explain how they calculated w for part a given "the inner diameter of the pump is 3.0 cm and the pump is depressed to 20.0cm with a pressure of 2.00atm" ?

kendal mccarthy

pKa is basically the hydronium concentration while pKb is the hydroxide concentration of a solution. pKa and pKb when added together always equals 14. You can calculate pKa or pKb from having Ka(equilibrium constant for acids) or Kb (equilibrium constant for bases) and taking the negative log.

kendal mccarthy

To determine which R to use view the givens you have and then you can determine which R unit would cancel out the appropriate units to get what value you desire. For most calculations, like in the VP=nRT equation, it will be 0.08206.

kendal mccarthy

if h2o is a gas, you include it in the ICE table. You only don't include substances that have a set amount of space they take up like a solid or a liquid.

kendal mccarthy

Because this is an exothermic reaction, an increase in heat will shift to the left because you can basically treat heat as you would treat an increase in a product on the product side. Having an excess of a product on one side will cause the reaction to go towards the reactants side in order to main...

kendal mccarthy

One trick I like to use is to look at the relationship between the variables of the PV=nRT equation. because P and V are on the same side of the equation that means they have an inverse relationship. This means an increase in one leads to a decrease in the other and vice versa.

kendal mccarthy

If Avogadro calls.... tell him to leave his number ;)

kendal mccarthy

Le Chatelier's principle basically is a principle that is used to help one determine what will happen in a reaction when different scenarios happen that would affect its equilibrium. By following Le Chatelier's principle one can determine the course the reaction will take to re-reach equilibrium.

kendal mccarthy

When solving these kinds of problems, the temperature will most likely be a constant because changing the temperature during a reaction will change the equilibrium constant.

kendal mccarthy

depending on whether the reaction is forward or reverse, then you can tell whether to add or subtract the change value.

kendal mccarthy

you can use this equation to gain information such as converting from concentration to pressure and vice versa.

kendal mccarthy

P is pressure
V is volume
n is moles
R is the ideal gas constant (8.314 J / mol·K)
T is temperature in Kelvin

kendal mccarthy

Are you talking about Kc? Because Kc itself doesn't have units because it is a constant. But in order to get a correct value for Kc there are units in the equation ([products]/[reactants]) that are represented by brackets, [ ]. These brackets represent molarity or mol/L.

kendal mccarthy

Q helps to determine or predict the path a reaction will take after a specific time. It can be compared to K to make assumptions about the reaction at hand.

kendal mccarthy

Yes, a reaction may occur with both aqueous and gaseous solutions. Depending on the question and data given that could help decide whether to use Kp or Kc.

kendal mccarthy

Test 1 will most likely cover the objectives from outline 1, which deals with chemical equilibrium. To study I would look over the problem sets along with the videos posted on the class websites. I would also make sure to do all the problems listed by the outlines to make sure that you have a firm g...

kendal mccarthy

K is a constant, meaning there are no units used. But, it is a good way to check your work if you end up with units because there should not be any because they should all cancel out.

kendal mccarthy

Lewis acids are lone pair acceptors. Lewis bases are lone pair donors. Bronsted acids are H+ donors. Bronsted bases are H+ acceptors. Bronsted acids are most always the same as Lewis bases because they always accept a proton by donating a lone pair. Bronsted acids are a special kind of Lewis acid be...

kendal mccarthy

A lewis acid is anything that is able to take in a lone electron pair. Usually it has a positive charge or can be a expanded octet.

kendal mccarthy

To reduce acid rain sanctions can be put in place on fossil fuel usage and power plants.

kendal mccarthy

The main drug discussed in class was cisplatin. Which is square planar and has 2 amine groups on one side and 2 chloride groups on the other side.

kendal mccarthy

What topics would you suggest to focus on for the final? Did anyone's TA give them a specific list of what type of problems or topics to study/ focus on?

kendal mccarthy

Bent can have either one lone pair: which makes an electron geometry of trigonal planar because three things around the central atom and therefore a molecular geometry of bent. it can also have two lone pairs: which makes an electron geometry of tetrahedral because 4 things around the central atom a...

kendal mccarthy

Sigma bonds would be stronger because of the overlapping orbitals while pi bonds don't have this overlap.

kendal mccarthy

I usually read the textbook and any concepts I have issues with I look for videos on Khan Academy!

kendal mccarthy

I think as long as you know the general trends of electronegativity that should suffice. If there are weird patterns that might not seem obvious my TA said the test would include numbers of electronegativity to help.

kendal mccarthy

I don't recall covering this so far, but I guess we will see on Wednesday!

kendal mccarthy

Look to see the electron geometries and molecular shapes to help you decide! For example if there are 2 atoms bonded and 1 electron then it is bent, if there are 2 atoms and 2 electrons it is also bent, if there are 2 atoms and 3 electrons it is linear because the lone pairs balance eachother out.

kendal mccarthy

A sigma bond is any single bond in a molecule, including 1 out of the 2 bonds in a double bond and 1 out of the 3 bonds in triple bonds. A pi bond is any 2nd or 3rd bond in a double or triple bond.

kendal mccarthy

You don't have to write subscribts for X or E if it is 1. Only for 2 and above!

kendal mccarthy

Yes, because in the ranking of powers of IMF's hydrogen bonding is a specialized kind of dipole-dipole bonding which is actually stronger, so if a molesule has H bonding it will be polar.

kendal mccarthy

T shaped is when the electron geometry is trigonal bipyrimidal because there are 5 regions of electron density around the CE and the Molecular shape is t-shaped because 3/5 of the regions of electron density are atoms and 2/5 are lone pairs.

kendal mccarthy

How often do I tell chemistry jokes on here?

~periodically~

kendal mccarthy

What kind of dogs do chemists have?

~laboratory retreivers~

kendal mccarthy

Ya it looks like the HW problems from outline 4 because it will be tested this week in discussion!

kendal mccarthy

I think the majority of what we will have to know are the basic trends. They also might give us numbers though if there are certain elements that don't stick to the status quo.

kendal mccarthy

I'm pretty sure it's graded on a weekly scale, but I'm not sure. I'll ask my TA and get back to you.

kendal mccarthy

My TA said

IMF, H bonding, molecular shape, VSPER, polarity from VSPER structure, bond angles, polar/non polar, intro sigma and pi bonds

kendal mccarthy

Yes some examples are H, He, Li, Be, B, and Al.

kendal mccarthy

combustion equations always have O2 on the reactant side and CO2 and H2O on the other, sometimes N2 depending on the organic molecule. 2C10H14N2 +27O2 ------> 20CO2+ 14H2O + 7N2

kendal mccarthy

Formal charges help you find the most probable structure and from there you can see if there could be resonance structures of that structure.

kendal mccarthy

I think they would tell you to write out the whole e- config or the short-hand one. They would definitely specify which to use.

kendal mccarthy

London dispersion forces happen because electrons moving can induce dipole forces due to attraction.

kendal mccarthy

This is kind of a joke but my class and I made a periodic table with pictures of literal moles, like the animal, and gave it to my teacher for April fools in high school. Kinda funny she was dying laughing.

kendal mccarthy

Electronegativity is the strength of an atom to attract an electron in a compound ex. in H2O oxygen has a electronegativity giving the oxygen a partial negative charge and the hydrogens a partial positive charge. Electron affinity is the energy released when an electron is added to an atom ex. Flour...

kendal mccarthy

yes. Non-polar molecules experience forces called Van Der Walls forces, which create a small dipole moment for a tiny amount of time when there is a difference in charge between two molecules. More polar molecules experience stronger dipole moments because of their innate polarity, meaning these for...

kendal mccarthy

electron affinity is the atoms affinity or how much an atom wants an electron and the energy it gives off when it obtains an electron. Ionization energy is the energy it takes to take away an electron from an atom. Usually, these trends follow a similar pathway on the periodic table as atoms who hav...

kendal mccarthy

The stronger the bond in covalent molecules, the more ionic character it possesses. So look for molecules with a difference in electronegativity to tell the strength of the bond. If they are similar it will not be as ionic, if they are different it will act more ionic.

kendal mccarthy

I don't think it is a requirement to use x, y, z. You should only have to write it as whatever quantum number it is and then "p".

kendal mccarthy

You can also post a comment and then scroll down to the comment you made and click on the number of posts you made and then it will tell you the date and time you posted.

kendal mccarthy

It is positive because ionization energy is the amount of energy required to remove an electron, which requires an input of energy. And it depends on the number of electrons and the number of subshells filled generally when dealing with ionization energies.

kendal mccarthy

Subshells are either s,p,d, or f on the periodic table.
Orbitals are inside subshells.
for example: s has 1 orbital, p has 3 orbitals, d has 5 orbitals, and f has 7 orbitals that each hold 2 electrons.

kendal mccarthy

What helps me is looking at the periodic table and counting how many atoms are in each subshell and pretending they are electrons, for example: for s subshells there are 2 atoms on the periodic table (2 electrons), in the p subshells there are 6 atoms on the periodic table (6 electrons), in the d su...

kendal mccarthy

This has to do with the number of valence electrons along with the increasing number of protons in the nucleus as you go from left to right across the periodic table. This trend causes the protons to have a greater pull over the electrons, thus leading to a smaller atomic radius.

kendal mccarthy

Based on the question and the given information, it's kind of like a puzzle where you can use certain equations or combine them to get the information you are looking for!

kendal mccarthy

E represents the energy of the photon, as it is the constant times the wavelength.

kendal mccarthy

How is the electron ejected if the energy of the photon is equal to that of the work function, meaning it has no KE? Because wouldn't it not be able to move if it has 0 KE?

kendal mccarthy

I'm pretty sure they are talking about black bodies. And I am not 100% sure if it will be tested ill ask my TA and get back to you! I don't think it will though because there is no module for black bodies on the class website and I think those are like the main concepts we need to know.

kendal mccarthy

Hi! It seems mostly the wavelength, distance from peak to peak, is measured in nm, nanometers, on most of the diagrams in the book for the EM spectrum. But I'm sure maybe the tests will have us convert units to use in other equations.

kendal mccarthy

I literally love this youtube channel for chemistry, I used it all throughout AP and regular chem in high school. His name is Tyler Dewitt. He is so succinct and I like his videos way better than crash course or any other teaching resource. Sometimes he can be a little slow so I usually watch on 1.5...

kendal mccarthy

Here is one i found that sent me: Old chemists never die. They just stop reacting!

kendal mccarthy

Ya I think as long as you can see the number of posts and the dates they were posted on it should be fine so even if there is a grading error there is still proof that you posted in the correct time frame.

kendal mccarthy

I like to think of photons like beads on a necklace or string, and each bead is a photon.

Search found 109 matches