CHEMISTRY COMMUNITY

Justin Lin 1B

I'm taking Life Science 7B and 7C over the summer!

Justin Lin 1B

The bonus question is worth 4 points

Justin Lin 1B

Final Exam is 9:30 am. Just watch out because tomorrow is Day Light Savings!

Justin Lin 1B

A helpful way to differentiate them is by looking at when they are consumed/produced in the reaction. A catalyst is consumed at first and produced in another step. An intermediate is produced from a step and then consumed in another step.

Justin Lin 1B

I would recommend doing the textbook problems and the UA worksheets! Also review any earlier topics that you might need to touch up on

Justin Lin 1B

You add Pt(s) or another inert metal into the cell diagram when there isn't a conducting metal present in the cathode or anode side.

Justin Lin 1B

You can figure our the overall order of the reaction by looking adding up the order of the reactions for each reactant

Justin Lin 1B

We would use the equation t1/2 = [A]o / 2k. This is also in our constants and formula sheet

Justin Lin 1B

I definitely agree with watching the Organic Chemistry Tutor. They do a great job of explaining the concepts I was confused about and their practice problems are very helpful!

Justin Lin 1B

From what I've noticed, all the problems should tell us if it's under acidic or basic conditions

Justin Lin 1B

We use Pt(s) when a side of the cell diagram doesn't have a solid conducting electrode

Justin Lin 1B

The reaction is still spontaneous; however, it would take an extremely long time for the process to occur

Justin Lin 1B

The max chem community points is 50.

Justin Lin 1B

I think it would be helpful to complete the assigned textbook problems and review the problems that you didn't get right. I would also focus on any topics or outlines that you might need to review.

Justin Lin 1B

Catherine Bubser 2C wrote:Is the oxidizing agent the molecule that has been reduced?

The oxidizing agent is the molecule that's being reduced

Justin Lin 1B

n is the number of electrons that are involved in our redox reaction. Make sure to balance out the charges though.

Justin Lin 1B

Hi! Because this is a redox reaction, you know that something that oxidation and reduction are occurring. You can't have an oxidation reaction without a reduction reaction. So because Br- is involved in oxidation, you can infer that ozone would have to be involved with reduction.

Justin Lin 1B

I would recommend Khan Academy and Chemistry LibreTexts! They are great resources that help clarify any confusion you might have on a topic

Justin Lin 1B

I think it's helpful to take a few deep breaths before the exam. It helps me concentrate and gets rid of the butterflies in my stomach.

Justin Lin 1B

It could be an isolated system if the lid is on. That way, no matter or energy can be transferred between the system and the surrounding.

Justin Lin 1B

The final will be cumulative

Justin Lin 1B

They should be the same thing. Lavelle just uses them interchangeably

Justin Lin 1B

A closed system and isolated system are different things. Energy can still be transferred through a closed system but not through an isolated system because it is insulated and doesn't allow matter or energy to transfer.

Justin Lin 1B

Reversible expansions are a longer process because of small changes that occur infinitely, so more work is done through this expansion. Irreversible expansion is a sudden expansion and does less work.

Justin Lin 1B

State functions are only dependent on their final and initial states, so the pathway through those states isn't important.

Justin Lin 1B

Make sure to look out for what units you are given. Those can help you determine what R constant would be the best to use.

Justin Lin 1B

Yes! Your explanation is exactly correct

Justin Lin 1B

Hi! I was also able to get the same answer as you

Justin Lin 1B

Delta U is defined as the internal energy of the system!

Justin Lin 1B

Hi! You should be able to review your exam with your TA during office hours.

Justin Lin 1B

Depending on your TA, they might give you a chance to make up the points that you missed during the week. I would definitely check with your TA because each one could be different when looking at chemistry community points

Justin Lin 1B

In a closed system, matter can't be transferred in or out of the system. There is no exchange of matter between the system and the surrounding. This means that the volume can't change because matter doesn't change.

Justin Lin 1B

When work is being done by a system, that means the system is losing energy and makes work (w) negative. If work is being done on a system, the surrounding is losing energy and that energy is being gained by the system, making work positive.

Justin Lin 1B

When looking at an acid, we are dealing with deprotonation because a proton is being removed from the acid. We use protonation for bases because it refers to the addition of a proton, which a base does by adding a hydrogen

Justin Lin 1B

I think the ones we should definitely know are the diatomic molecules like O2, H2, Br2... Lavelle also mentioned multiple times that graphite (solid) is carbon's most standard form, so I think we should know that as well.

Justin Lin 1B

I would assume X to be insignificant when the K value is 10^-5. You can double check that your approximating correctly by using the 5% rule.

Justin Lin 1B

I think making a planner is helpful and can keep you motivated. It helps keep me on track by seeing what I just need to finish for that day. I know once I'm done with that day, I'll have some time to relax and take a break from work.

Justin Lin 1B

Depending on if the reaction is endothermic or exothermic, the temperature will have a different effect on K. Raising the temperature in an exothermic reaction will favor reactant formation instead of product formation. This will make your K value smaller. If you raise the temperature in an endother...

Justin Lin 1B

When a bond breaks, it requires energy to do so. Forming a bond will release energy

Justin Lin 1B

We would determine the x value by the stoichiometric coefficient!

Justin Lin 1B

I recommend doing the UA worksheets and assigned textbook problems. They provide good questions that could look like something similar to the midterm. I would also rewatch some lectures to review any information he covers because some questions can come straight from the lectures.

Justin Lin 1B

Having a larger Ka value means that it is a stronger acid, relative to weak acids when comparing their strengths.

Justin Lin 1B

We should be taking it during our respective lecture time.

Justin Lin 1B

Here's a chart of all the strong acids and bases. Anything not listed on the chart would be considered a weak acid/base.

https://sites.google.com/site/chempendi ... cids-bases

Justin Lin 1B

For x to be negligible, our equilibrium concentration needs to be a value smaller than 10^-4. Professor Lavelle also mentioned in his lecture that we can verify the approximation if x is less than 5% of the initial concentration given to you.

Justin Lin 1B

Temperature will change the K value. For example, if a reaction is endothermic and you heat up the reaction, the forward reaction will be favored and more products will be produced. When looking at how to solve the equilibrium constant (K). More product on the numerator will mean a larger K value. P...

Justin Lin 1B

Yes you would square root the Kw value because water is neutral, so we know that [H3O+] and [OH-] have to be the same value.

Justin Lin 1B

Since Carbon is a solid, there is only 1 mole we take into account when comparing the moles in reactants and products. H2 and CO are both in the gas phase so there are 2 moles accounted for on the product side. Because there are more moles on the product side 1<2, the reactant side is favored

Justin Lin 1B

Hi! I think there is a mistake with your quadratic equation. For your problem I got 4x^2 - 23.2x + 4.96. I think it should be -23.2x instead of -17.2x for your quadratic equation. Hopefully this helps!

Justin Lin 1B

I also got 3.9 too, but it was the rounding that could get your equilibrium constant to be 3.88. When I calculated the equilibrium concentration of H2, I got .1566 but it can round to .157. So if you use .157 instead of .1566 when solving for K, you should get 3.8. I hope this helps!

Justin Lin 1B

Hi! You are correct that we only take the gas phase molecule into account when calculating K or Q. We would exclude the solids and liquids from being in our calculation

Justin Lin 1B

K and Q are calculated the same way. Q helps determine which direction a non-equilibrium reaction will proceed. When you calculate Q at any time during the reaction, you can compare it to K to determine which way the reaction is favored/shifted towards. If Q<K, that means that there are more reactan...

Justin Lin 1B

I highly recommend attending the UA sessions. The step up sessions and workshops are both good ways to increase your understanding of what Lavelle has taught that week. I would also recommend doing the online textbook questions he assigned. They are optional, but they are great practice problems tha...

Justin Lin 1B

When the denominator has a greater value, that means the equilibrium constant(K) will have to be a value less than 1. When the equilibrium constant is less than 1 (K<1), it means there is a slight favoring of the reactants.

Justin Lin 1B

Bent and angular refer to the same shape. Their names can be interchangeable.

Justin Lin 1B

NayeliPlayas_2J wrote:Has Dr.Lavelle mentioned anything regarding final exam scores?

Yes! He sent an email yesterday that our scores will be done by Saturday

Justin Lin 1B

You would use -ate for the transition metal when the charge of the coordination sphere has a negative charge

Justin Lin 1B

What did the other elements say to the hydrogen?

What a loner!

Justin Lin 1B

At least for 14A, we wouldn't have to determine if the coordination compound is square planar or tetrahedral.

Justin Lin 1B

My TA said that we would join a zoom link and there would be two proctors this time.

Justin Lin 1B

https://lavelle.chem.ucla.edu/wp-conten ... pounds.pdf

Here is a list of ligands that one of the UA shared with us. I hope this helps!

Justin Lin 1B

Complex ions do have importance in biological processes. An example Professor Lavelle uses is the Heme complex, which is a tetradentate ligand that bonds to an Iron. The heme complex bonded to a histidine creates a myoglobin where the Iron picks up and binds to an O2. Hemoglobin has 4 similar myoglo...

Justin Lin 1B

The length and the lewis structure of the molecule can play a role in determine if something is polydentate. An example of a polydentate is C2O4. After drawing its lewis structure, we can see that the 2 Carbons act as spacer atoms which give the single bonded oxygens room to orientate themselves in ...

Justin Lin 1B

A monodentate is a ligand that can only form 1 bond with a transition metal. A polydentate is a ligand that is able to form multiple bonds with the transition metal. A molecule like CO would be a monodentate because only one of the lone pairs from the carbon or oxygen can pair to the transition meta...

Justin Lin 1B

The coordination number is the number of atoms/molecules bonded to a transitional metal. Anything inside of the bracket is part of the coordination sphere and connected to transition metal central atom. There are 4 NH3 molecules and 2 Br atoms attached to the transition metal, so the coordination nu...

Justin Lin 1B

That's correct! The molecular shape of the molecule will give you its bond angles.

Justin Lin 1B

Molecules that Trigonal Planar, Trigonal bipyramidal, or Seesaw contain 120 degree bond angles. Bent(AX2E) also has bond angles that are slightly less than 120 due to the lone pair on the central atom. I hope this helps!

Justin Lin 1B

Like someone said above, molecules that are bent will have an A-X-E notation of either AX2E or AX2E2. The X represents bonded atoms to the central atom and E represents the lone pairs to the central atom. So any molecule that has two bonded atoms and a lone pair or two bonded atoms and 2 lone pairs ...

Justin Lin 1B

To find the hybridization of the oxygen atom in CH4O, we just have to look at how many regions of electron density are present on the oxygen atom like the bonds connected to it and lone pairs

Justin Lin 1B

I'm not sure if we're able to discuss the midterm questions on chem community but you're able to review the midterm questions with your TA during their office hours.

Justin Lin 1B

I would definitely recommend attending the UA sessions. I know some of the UAs are going to have a finals review session. I would also do all the textbook problems and I found them to be helpful practice for the midterms.

Justin Lin 1B

Lone pairs do count as their own region of e- density

Justin Lin 1B

Hydrogen can only form 1 bond so it wouldn't be favorable to have it as the central atom.

Justin Lin 1B

To determine whether a molecule with a double bond is linear or bent, you look at how many lone pairs and bonding pairs there are connected to the central atom in the molecule. Water is bent because there is a lone pair with 2 bonding pairs connected to the central atom. A molecule with double bonds...

Justin Lin 1B

Any molecule with 2 lone pairs and 2 bonding pairs is called bent. Bent is its official name

Justin Lin 1B

If you draw out the lewis structure for NO3-, there will be two oxygens that share a single bond with the Nitrogen and one oxygen that will share a double bond with the Nitrogen. When you take the formal charge of Nitrogen, you should get 1, which means it has a +1 formal charge.

Justin Lin 1B

The answers would most likely be multiple choice so we wouldn't have to draw them, but we should choose the structure with the lowest formal charge because those are the best represented structures.

Justin Lin 1B

Hi in your example, BF3 would be the Lewis acid and F- would be the Lewis base. If we count up the electrons in BF3, we would get a total of 24 electrons. When we draw the lewis structure for BF3, we'll see that there aren't enough electrons available to complete Boron's octet and it only has 6 elec...

Justin Lin 1B

The ground state configuration for Ta would be [Xe] 4f14 5d3, 6s2. If we look at the 5d orbital, there are 3 unpaired electrons present.

Justin Lin 1B

An intermolecular force occurs between two molecules while and intramolecular force occurs within a single molecule.

Justin Lin 1B

I'm not sure if we would be given those but an easy way remember them though is by looking at the what group the atom is in.Group 1 has a +1, Group 2 has a +2, Group 13 has a +3, Group 14 has +-4, Group 15 has -3, Group 16 has -2 and group 17 has -1. These are determined from the valence electrons i...

Justin Lin 1B

We use formal charge to determine what Lewis Structure would be the most stable. We preferably want a Lewis Structure that has a zero charge or close as possible to a zero charge.

Justin Lin 1B

Electronegativity decreases going down a group and increases going across a period from left to right.

Justin Lin 1B

When an atom is isoelectronic, that means they have the same number of electrons. An example can be K+ and Ar because they both have 18 electrons. They might share the same number of electrons, but they still have their own different properties.

Justin Lin 1B

The expanded octet can be applied for elements starting from period 3 and below

Justin Lin 1B

The electron configuration for Cr would be [Ar]3d^5 4s because it has an exception of moving one electron for the 4s to fill the orbital in the d block, making it more stable

Cr+ should be [Ar] 3d^5 because it gives up the lone electron in the 4s block and it becomes positively charged (cation)

Justin Lin 1B

When we write the electron configurations, it can just be written out as p^6.

Justin Lin 1B

As you move down a group, the ionic radius increases. It increases because a new electron shell is added to each row that are further from the nucleus. The ionic radius also decreased moving from left to right across the period because electrons are still in the same shell and the increasing nuclear...

Justin Lin 1B

Cations would be smaller than the original atom because of less electron repulsion while anions are larger because of more electron repulsion

Justin Lin 1B

Row 3 and after that have an expanded octet because it's in the 3rd energy level

Justin Lin 1B

Light with a wavelength of 190 nm is incident on a metal surface. The most energetic electrons emitted from the surface are measured to have 4.0 eV of kinetic energy. Which of the metals in the table is the surface most likely to be made of - Aluminium (4.08 eV), Calcium (2.9 eV), Potassium (2.3 eV...

Justin Lin 1B

10^-15 is like the borderline for what can be detected for having wavelike properties. Anything over 10^15, like 10^-38 in your question, is too small for wavelike properties to be detected.

Justin Lin 1B

ΔP = M * ΔV If we want to solve for the uncertainty in velocity (ΔV), we have to rearrange the variables so ΔV can be by itself. To do this we just divide the mass over to the other side. This now makes the equation for finding ΔV = ΔP/M. The numerator for this equation would be ΔP and the denominat...

Justin Lin 1B

You should always make sure that the mass is converted to kilograms because you'll be able to work with the SI units. Some of the conversions are on the constant sheet we were given, but there are other conversions not on the sheet that we should memorize.

Justin Lin 1B

My TA said that it's best to apply sig figs until you get your final answer

Justin Lin 1B

Please explain the correct answer to this question. Thank you! Hey! When you look at the electron's transition from n=5 to n=1, there is a high energy gap between those levels. The larger your energy gap is, the more energy is being emitted. Energy and frequency are proportional to each other, so h...

Justin Lin 1B

Hi! For the second question, we are looking for the Kinetic Energy of the electron (KE) so we use the equation KE = E - Work Function. Part A indirectly gives us the work function (7.22 x 10^-19) because the minimum energy required is also equal to the work function (the threshold energy). Now that ...

Justin Lin 1B

Hi! Both constructive and destructive interferences result in a diffraction pattern. The patterns are different for whatever interference is used.

Justin Lin 1B

The m value represents the mass of an electron which is (9.11 * 10^-31). For the velocity, you don't need to make any conversions because the units are already correct as m.s-1

Justin Lin 1B

Hey to solve this question, you want to start by finding the Energy of the photon. Use E=(h)(c)/wavelength because we are given 1850 nm (wavelength). Plug the wavelength into the equation and your energy of the photon should be 1.074*10^-19. Now we want to find the amount of photons that are generat...

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