CHEMISTRY COMMUNITY

Eliana Witham 2H

If one species is a gas, then a solid inert electrode is also needed such as Pt. Also, in the example that you gave, both Ti2+ and Ti3+ are in the solution and are aqueous, so they can be separated by a comma since there is no phase difference and they are in contact with each other. And another tip...

Eliana Witham 2H

You use R= 8.314 J/(Kmol). If you look at the units, we know that delta G and delta G nought are in J/mol. Therefore, RTlnQ needs to be in J/mol, too. When R is in J/(Kmol) and temperature is K, then the final product of RxT is in J/mol, which is what you want.

Eliana Witham 2H

I like to write down the given variables and what the problem asks for first. Then, it's easier to look for an equation with those variables. Also, the equation sheet gives the kinetics equations in order of 1, 2, then 0 order.

Eliana Witham 2H

We know that deltaU = q + w, and the question actually gives you the values for q and w. For a constant pressure, deltaH = q. Also, work is done on the system, meaning that your given work value is positive. You can add these numbers for the answer.

Eliana Witham 2H

Kaley Qin 1F wrote:There is a review sheet called ENDGAME for this year

That's what I was looking for, thank you!

Eliana Witham 2H

What are the names of some worksheets posted on here for final review? More specifically, what is the name of the final review from last spring; it has a name like the "dino nuggets" worksheet, but I forgot what it was.

Eliana Witham 2H

For these intermediate values, neither reactants or products are strongly favored. However, there are more products if K>1, and more reactants if K<1. When K=1, there are equal amounts of reactants and products (neither is favored).

Eliana Witham 2H

The slowest step determines the rate because the overall reaction cannot be completed until the slowest step is finished. A real life analogy could be if you're hiking with friends and one person is slower than the others, the hike is not complete until that person gets to the end, too.

Eliana Witham 2H

When I want to make a quick meal, the frozen fettuccine alfredo from Trader Joes is so good!

Eliana Witham 2H

An inert conductor is useful because it does not participate in the reaction (unreactive), but it is a source of electrons. Examples of inert conductors are graphite, platinum, gold, and rhodium, while some reactive electrodes are copper, zinc, lead, and silver.

Eliana Witham 2H

In 14A, the final's content was based on the amount of time we spent on each topic. So, thermodynamics will probably be a large part of the test.

Eliana Witham 2H

Thank you so much, Dr. Lavelle, for being such a supportive and caring professor! You have been so helpful throughout this class, and I'm sure everyone appreciates your effort. Also, thank you to the TAs and UAs for providing hours of extra help!

Eliana Witham 2H

I think it's necessary to know the basic rules for oxidation states. You need to be able to assign oxidation numbers to the atoms in a reaction in order to balance it and understand what is being oxidized and reduced. Sapling has a lot of practice from this week where you have to assign oxidation nu...

Eliana Witham 2H

For Au, all single atoms have an oxidation number of 0. In HAuCl4, you assign -1 to Cl and +1 to H. Therefore, you have -4 from Cl4 and +1 from H, so Au's oxidation number must be +3 to balance the overall charge of 0. Au is oxidized by losing 3 electrons. You can go through the same process to see ...

Eliana Witham 2H

A monatomic ion consists of one atom. The K in both compounds will be a K+ ion, while the Cl is Cl- in KCl and ClO4- in KClO4-. Therefore, Cl would not be a monatomic ion in ClO4- because there is also oxygen in the ion, making it polyatomic.

Eliana Witham 2H

You put the anode on the left and cation on the right. Then, you separate the aqueous ions by a double line, representing the salt bridge. On either side of the ions, you write the solids separated by a single line. Also, if there are multiple solids or ions in the cathode or anode, make sure you wr...

Eliana Witham 2H

You can type in the ions using the provided buttons that appear when you click in the box. There's a button that lets you put a superscript, or you could probably also use the ^ icon on your keyboard.

Eliana Witham 2H

E (cell potential) is a path function because it depends on the path taken, or which substance was reduced and which was oxidized.

Eliana Witham 2H

The entropy of the universe is always increasing, but individual reactions can have a decrease in entropy. For example, a phase change going from liquid to solid is a decrease in entropy because there is more order in a solid than liquid.

Eliana Witham 2H

I'm going to Palos Verdes today for a walk. If you're in Westwood, it's about 45 minutes away, I recommend it!

Eliana Witham 2H

At constant pressure, you can use deltaU = deltaH - P(deltaV) because q=deltaH and w= -P(deltaV).

Eliana Witham 2H

I don't think you can use the second equation because constant volume assumes that w=0. Therefore, deltaU = q, and you use that equation. However, when there is constant pressure, work is done and you use deltaU = q + w.

Eliana Witham 2H

First, you need to think about what equation is useful. For this problem, you'll want to use ΔG = ΔG∘ + RTlnQ. You can find Q by using the partial pressures and coefficients in the problem (we learned about Q before the first midterm). Then, you just need to plug in the information given. Also, keep...

Eliana Witham 2H

You have to first find the change in entropy when the volume changes. Then, find the change in entropy when the temperature changes. Use the equations nRln(V2/V1) and nC(v,m)ln(T2/T1). These equations added together will give you the answer!

Eliana Witham 2H

It's easiest to picture the liquid state vaporizing into a gas. If there is a great increase in disorder, then you can think about the liquid being very ordered at first so that it has more room to become disordered when vaporizing. If the liquid is already more disordered, then it won't have as gre...

Eliana Witham 2H

Yes, the equation you wrote should be correct. Make sure that you get a negative answer since volume and temperature are decreasing and that you are using the correct R value!

Eliana Witham 2H

As everyone else said, the final was a bit more difficult. I did find that the UA's had some insight into the types of questions that Dr. Lavelle likes to ask, so going to as many review sessions as possible along with redoing textbook problems helped a lot.

Eliana Witham 2H

You want to use the equation q=mCdeltaT. First, you can solve for delta T, which is 200 degrees C. Then, you can use deltaU=q+w to find q. w is negative and deltaU is positive. Finally, you can plug these numbers into the original equation to get C.

Eliana Witham 2H

For #10, I actually did put a negative in front of q(water). I used the equation deltaH(fusion) + q(ice) = -q(water). This equation worked for me!

Eliana Witham 2H

To change Cp to Cv, you can use the equations (given on the sheet) Cp=(5/2)R and Cv=(3/2)R. With some algebra, you get Cv=(3/5)Cp.

Eliana Witham 2H

If you look under grades on the CCLE site, it should be there!

Eliana Witham 2H

Yes, you only count the moles of gas. If you think about it conceptually, liquids and solids cannot change volume, but gases can.

Eliana Witham 2H

It helps me to picture a potential energy diagram. A temperature increase favors the side that is higher on the graph. In an endothermic reaction, the higher side is the products, so K will increase. In an exothermic reaction, the higher side is the reactants, so K will decrease.

Eliana Witham 2H

I agree, the midterm was definitely not as easy as 14A! But, it only harms you to dwell on things that you can't control. Try to remain positive and change your study techniques for the next test. Also, remember that one bad test doesn't mean that this class is not for you, it just means that you ha...

Eliana Witham 2H

Water won't affect the reaction because it is the solvent. Even though glucose is dissolved in water, you can think of it as though adding water will have barely any noticeable effect on the concentration of glucose since there is so much more water than glucose. It helps to think of Dr. Lavelle's e...

Eliana Witham 2H

I think that the wording is just confusing, but you have the right concept. Equilibrium composition refers to the concentrations of reactants and products present at equilibrium. So, equilibrium composition can change while K remains constant. For example, when there is a forward shift, more product...

Eliana Witham 2H

I would solve this by using the equation nitrous acid forms hydrogen ions and nitrite. Then, you set up an ICE table. The initial value of nitrous acid is given, and the initial value of nitrite is .15 M because potassium nitrite completely dissociates. Initial for hydrogen ions is 0. Then, you can...

Eliana Witham 2H

X is insignificant when it is less than 5% of the initial molarity of the reactant after approximating. In general, you can use the approximation when K<10^-4. As for why we do this, it is because omitting the x will cause negligible change in the final answer since K is so small. It's easier to sol...

Eliana Witham 2H

I would solve this by using the equation nitrous acid forms hydrogen ions and nitrite. Then, you set up an ICE table. The initial value of nitrous acid is given, and the initial value of nitrite is .15 M because potassium nitrite completely dissociates. Initial for hydrogen ions is 0. Then, you can ...

Eliana Witham 2H

Which UA sessions this week are review for the midterm? I can't seem to find out whether they're going over new info or doing a review of weeks 1-3.

Eliana Witham 2H

If you're still having trouble understanding this, Dr. Lavelle went over this concept in lecture 3. It's called Le Chatelier's principle.

Eliana Witham 2H

I believe we only really used this equation to convert between pressures and concentrations. This would be helpful in a chemical equilibrium problem that asks for Kp or Kc, and you need to convert values.

Eliana Witham 2H

To add on to everyone else's posts, when you add an inert gas, they do not participate in the reaction because they have a full outer shell. Therefore, they are unreactive and will not cause changes to the partial pressures of the other gases.

Eliana Witham 2H

Which types of compounds exhibit autoprotolysis? I understand what it is, but are there certain types of substances besides water that exchange protons regularly? Do all weak acids or bases do this?

Eliana Witham 2H

Yes, this is correct! Also, you can use reverse reactions with the equilibrium constant 1/K, and you can multiply equations by a number to get new coefficients. The equilibrium constant would be raised by that number, K^x.

Eliana Witham 2H

Also, if you are given gas concentrations instead of partial pressures, it is ok to find Kc unless the problem states otherwise.

Eliana Witham 2H

I can't tell what you did wrong from this information, but I can give some suggestions. Make sure you are using the correct value for Kb. Then, make sure to pay attention to the problem. X will be the concentration of OH-, not H3O+. You might be confusing pOH with pH.

Eliana Witham 2H

In lecture, I remember Dr. Lavelle saying how not many concepts from 14A will appear directly. One that will appear again is lewis structures. Thermodynamics and some other topics are very different from 14A material.

Eliana Witham 2H

It helps to visualize this as well. If you increased pressure on a solid, it wouldn't change. Same with a liquid, it wouldn't change volume. However, if you increase pressure substantially on a liquid, it could turn to a solid.

Eliana Witham 2H

The equations that have only unrelated compounds, such as the last equation, would not be useful. The extra equations were added to make the problem more difficult- you have to find the equations that could be added to get the reaction you want.

Eliana Witham 2H

For the first one, when volume is compressed, that means that, since the moles stay the same, the concentration increases. Therefore, you shift towards the side that has less moles of gas. The reactant side has 3 moles of gas, and the products have 2 moles of gas. For the second one, the reaction is...

Eliana Witham 2H

With ideal gasses, you assume that there are no attractive forces taking place between molecules, the volume is negligible, the particles are constantly in motion, and all collisions are elastic. Essentially, the particles only have kinetic energy and no potential energy.

Eliana Witham 2H

Adding to Mohamed's answer, the heme complex can bind to oxygen and histidine, indicating that it has 6 e- density regions.

Eliana Witham 2H

I think (not exactly sure) that in some cases like strong acids/bases, solutions that are negatively charged are acidic and positively charged are basic. This would be because when acids dissociate, the products will be an anion and H+ ion. The anion will make the solution negative. The same reasoni...

Eliana Witham 2H

I think you should have the right answer if you change grams to kilograms!

Eliana Witham 2H

Acid rain is caused by the reaction of carbon dioxide with water, which produced carbonic acid. Therefore, anything that reduces carbon dioxide in the air could reduce acid rain. An example would be switching to more renewable energy sources and burning less fossil fuels.

Eliana Witham 2H

From the lectures, a ligand is a lewis base that forms coordinate covalent bonds with a transition metal cation. That's all I have in my notes for the definition!

Eliana Witham 2H

-ate is added when the coordination complex has an overall negative charge.

Eliana Witham 2H

If this happened on the final and it was because you mixed up final and initial, you could also just reread the problem and look at whether the energy level needs to be above or below n=4. Because light was emitted, the answer should be n>4.

Eliana Witham 2H

emilyyribarren1k wrote:Will we need to have this memorized? Also does anyone know if we can use the common ligand table on the final or if this type of information will be given to us in the question?

I know that the final is closed book, so I'm preparing to only get a periodic table and formula sheet.

Eliana Witham 2H

For octahedral, when you create a shape out of the atoms, making each one a vertex, then you get an octahedron. This shape has 8 faces, hence the name. If you look up the shape online, it will make more sense!

Eliana Witham 2H

Dipole arrows represent the dipole moment in a molecule. The arrow points towards the more electronegative atom. For example, water has an arrow pointing towards the oxygen in between the hydrogens representing the net dipole moment.

Eliana Witham 2H

The more electrons there are, the more electron shielding there is. Therefore, another molecule will more easily distort (or pull) the electrons in the large molecule, creating greater LDF's.

Eliana Witham 2H

For memorizing the shapes, it's helpful to visualize them in a way that connects to their name. For example, it helps me to visualize trigonal bipyramidal as a triangle formed by 3 atoms and the other 2 atoms are the tips of 2 pyramids. This is much more useful than thinking of the regular lewis str...

Eliana Witham 2H

Happy Thanksgiving (3 days late)! My aunt usually makes potstickers as an appetizer!

Eliana Witham 2H

All you have to do is count the number of atoms bonded to that atom, and add this number to the number of lone pairs. sp corresponds to 2, sp2 to 3, and so on.

Eliana Witham 2H

I think (not sure) it would be better to put the unpaired electron on the oxygen because the formal charge on both O and Cl would be 0. However, if the unpaired e- was on Cl, then Cl would have FC= +1 and O's FC= -1. This is less favorable.

Eliana Witham 2H

For valence electrons, you only want to count the number of electrons after the last noble gas' configuration. For this example, you would look at the e- configuration [Ar]3d3. Therefore, the textbook answer would make more sense!

Eliana Witham 2H

The general trend is that ionization energy increases up and across the periodic table.

Eliana Witham 2H

In the notes, the only exceptions are Cr and Cu. But, it makes sense that Ni would want to fill its d orbitals as well. I think you could write Ni's electron configuration both ways. Also, for the Ni2+ cation, the highest energy electrons will be lost first. Therefore, the 4s electrons will be lost ...

Eliana Witham 2H

How many possible hydrogen bonding sites does guanine have? I think it's 11, but I want to be sure. Thanks!

Eliana Witham 2H

Interaction potential energy is the 2 polarizabilities of each molecule/atom multiplied together and divided by distance^(6). This equation means that when polarizability increases, the strength of the attractive interactions increases. Also, when distance increases, the interaction strength decreas...

Eliana Witham 2H

Your'e correct! The resonance hybrid is an average of all the individual resonance structures drawn for a molecule. Resonance hybrids are more accurate than resonance structures because the represent bond lengths better. In any molecule that has more than one type of bond and has resonance structure...

Eliana Witham 2H

Looking back at notes, it was mentioned towards the end of lecture 10. It is the net positive charge on an electron in an atom. Inner electrons will shield outer electrons from the electrostatic attraction of the nucleus (+). Therefore, outer electrons feel reduced electrostatic attraction, and this...

Eliana Witham 2H

A full 4d subshell is a more stable electron configuration. The 4d subshell is lower in energy than the 5s subshell, so the new e- configuration is lower in energy.

Eliana Witham 2H

Yes, if you are dealing with copper or chromium, they will have more stable electron configurations with full or half-full 3d subshells. N=3 is lower in energy than n=4.

Eliana Witham 2H

I like to draw the lewis structure and make sure the electron count is correct first. Then, I'll find the formal charges and draw a new lewis structure if it lowers the formal charges. Hope that helps a little!

Eliana Witham 2H

SO2 has a bent shape, which I believe causes it to be slightly polar and have dipole-dipole forces. Also, to answer the second question, hydrogen bonds are actually a type of dipole-dipole force, so yes!

Eliana Witham 2H

This is one of the exceptions to writing electron configurations (the other is a d^5 subshell). Having a full 4d^10 subshell has a lower energy and is thus more stable than having a 4d^9 subshell. Another example of when this occurs is with copper and chromium.

Eliana Witham 2H

An easy way to think about this is to ask yourself what the easiest way to get to a full valence shell is. Would it be more simple to lose or gain electrons? For example, for +1 cations, it is much easier to lose one electron than to gain seven electrons.

Eliana Witham 2H

It also depends on the ion. If you're talking about a cation, then it lost electrons so there are less electrons than in the neutral state configuration. If you're talking about an anion, then it gained electrons so there are more electrons than in the neutral state configuration.

Eliana Witham 2H

I believe that all salts have ionic bonds. Any compound with an anion and cation is labeled as an ionic compound/salt.

Eliana Witham 2H

No, the atomic radius gets smaller which the last post explains. The exception, however, is that the radius increases from the nitrogen atom to the oxygen atom because of the extra electron-electron repulsion. Oxygen has 2 electrons in one orbital, whereas nitrogen does not.

Eliana Witham 2H

Happy day-after Halloween! I did scary clown makeup and hung out with a couple close friends and cousins. We ordered pizza and set up a projector in my backyard to watch the Nightmare on Elm Street!

Eliana Witham 2H

L indicates the particular subshell. 0 corresponds to s, 1 corresponds to p, and so on. If you know the values for l and n, then you know how many electrons are possible for that atom. For example, if l=2, then you know the atom reaches the d subshell. You then know that there are 5 orbitals for the...

Eliana Witham 2H

Hi,

How would you write the electron configurations for the Chromium ions? Also, how do you write the electron configurations for cations in the d block in general?

Eliana Witham 2H

These exceptions apply to chromium and copper. When writing chromium's electron configuration, you have [Ar]3d^(4)4s^(2). However, to get the lowest energy and therefore the most stable configuration, you want to put one electron from the 4s subshell into the 3d subshell so that there are 6 unpaired...

Eliana Witham 2H

Adding on to Charlene's answer, you can use the equation (uncertainty in momentum)=(mass)(uncertainty in velocity) to substitute for uncertainty in momentum in Heisenberg's Indeterminacy Equation. Therefore, you can get the final answer using only one equation.

Eliana Witham 2H

I may be wrong, but I believe the answer is middle option. You are correct that the work function is the energy required to remove an electron. You have to convert kJ/mol to J/photon. In order to do this, you can use conversion factors to convert kJ to J, then multiply this by (1 mol/ 6.02x10^23 pho...

Eliana Witham 2H

If you draw 7 energy levels, you can visualize all of the possible changes in energy level. There are six levels below n=7, so there are 6 spectral lines that can appear. The wavelength range will be between the shifts of n=7 to n=6 and n=7 to n=1. The highest wavelength corresponds to the lowest en...

Eliana Witham 2H

Hi, I am confused what to do in this problem:
Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom.

The diameter was given in the problem, then you can find the uncertainty in velocity, which I understand how to do. What would this model look like, though?

Eliana Witham 2H

When we get the final answer using the Heisenberg Uncertainty Equation whether it is delta x or delta p or delta v, what does this value mean conceptually? Could someone please give an example of how you could apply the answer to a real world situation? I'm mostly confused about the inequality symbol.

Eliana Witham 2H

I think you should definitely know this just in case. It's a concept from high school chemistry- only the ions that are used to make the product and the precipitate are included in the net ionic equation. No spectator ions are included.

Eliana Witham 2H

That's interesting, thank you!

Eliana Witham 2H

This problem is asking you to find M(x)S(x), which is the metal sulfide. You know the molar mass of the metal by subtracting the molar masses of 2 oxygen and 2 hydrogen atoms from 74.10 g/mol. You also know the charge is +2 because hydroxide is -1, and there are two hydroxide ions. Then, the sulfide...

Eliana Witham 2H

In yesterday's lecture, Dr. Lavelle mentioned that x-ray diffraction is easier to use/more available than electron diffraction. Why is this, and what is the difference in results when using these two methods?

Eliana Witham 2H

Electrons are not emitted when they transition between energy levels. The arrow he drew going down represents an excited electron moving back to ground state. This will emit a specific amount of energy; every atom and molecule has unique amounts of energy they absorb/emit, and electrons never stay b...

Eliana Witham 2H

It was just that the wording was a little confusing. He meant that when the energy of the photon is greater than or equal to the energy to remove an electron, electrons are emitted. All other times, electrons are not emitted.

Eliana Witham 2H

Hi! Adding on to this, I think the most important concept to know is that increasing the intensity of light does increase the number of photons, but if no electrons are being ejected to begin with, this will not result in ejected electrons. One photon can eject one electron, so the energy of each ph...

Eliana Witham 2H

Thanks everyone!

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