CHEMISTRY COMMUNITY

Ethan Laureano 3H

I did that the day before the final. Only advise to do so if you already have a decent foundation on the topics and were paying attention during all the lectures.

Ethan Laureano 3H

I enjoyed quantum and I like anything that is math-oriented.

Ethan Laureano 3H

Starting O-Chem with Chem 30 o.0. Wishing everyone good luck on their future classes.

Ethan Laureano 3H

Just know that regardless of what score you get, it won't define you. If you do see a score you do not like, just know that you'll forget about that score months from now. It is not the end all be all! As long as you know you put in your best work, you should be proud.

Ethan Laureano 3H

Just temperature :)

Ethan Laureano 3H

Overall order of the reaction equals the sum of all the orders of the reactants.

Ethan Laureano 3H

Just meeting new people and socializing! It gets lonely on zoom uni.

Ethan Laureano 3H

If you have trouble memorizing ([M] vs time is zero; ln[M] vs time is first; 1/[M] vs time is second) then it would be best to derive from the integral using the rate law (-d[A]/dt) and the differential rate law (k[A]^m) like how Dr. Lavelle does in the lectures.

Ethan Laureano 3H

Since the units of the rate law are the same, then the units for K has to change depending on whether the reaction is zero order (no M), first order (M), or second order (M^2).

Ethan Laureano 3H

The n is the moles of electrons transferred. This can be found by figuring out the oxidation numbers of the reactants and products, making two half reactions, and determining the amount of electrons introduced or released in each half reaction.

Ethan Laureano 3H

Acid uses hydronium to balance the H and basic uses hydroxide. They both use water to balance O.

Ethan Laureano 3H

Bring your pipes :)

Ethan Laureano 3H

I think Mackenzie is right

Ethan Laureano 3H

I believe for the anode, since electrons are leaving, the solid turns to the aqueous form of the element and enters the solution (Ex. Ag to Ag + assuming the anode is Silver). Since the cathode is in a solution with aqueous ions, the electron from the anode reduces the ions in solution adding to the...

Ethan Laureano 3H

E naught signifies standard conditions (1 M, 25 C, 1 atm) and does not get affected by change in concentrations, unlike E.

Ethan Laureano 3H

Constant pressure since q_p=deltaH

Ethan Laureano 3H

It helps to know your units and write them out so you know if the R-value chosen cancels the units out.

Ethan Laureano 3H

All I know is that the anode is for oxidation and the cathode is for reduction. Since conventionally speaking, oxidation is the left cell and reduction is the right, you can think of it as anode is the left and the cathode is on the right.

Ethan Laureano 3H

Hello fellow Biochem majors. I was checking the handbook that we were given during orientation and it suggests I take chem 30A next quarter. However, when I check the pre-reqs of the class, it does not list chem 14B as one? Would I still be able to take this class? Thanks for the help in advance! :)

Ethan Laureano 3H

I am craving some Alaskan King crab.

Ethan Laureano 3H

If you recall the sapling homework, if both delta H and delta S are positive, then the equation would be deltaG = deltaH - TdeltaS. In order to label a reaction spontaneous, deltaG must be negative. At low temperatures, -TdeltaS might not have a high enough magnitude to overcome deltaH and result in...

Ethan Laureano 3H

Hess's law, bond enthalpies (least accurate), and standard enthalpies of formation.

Ethan Laureano 3H

A positive delta G denotes the need for energy for the reaction, thus indicating it is not spontaneous (occurring without external energy).

Ethan Laureano 3H

Would it be analogous to Q and K, where Q is G and K is G^o

Ethan Laureano 3H

If you are talking about S, then it is only positive values. If you are talking about delta S (which I assume you are), then it would depend on the values used in the equation to derive delta S. You can also think of it conceptually (if it is a phase change from solid to liquid or gas, then degenera...

Ethan Laureano 3H

Go to as many workshops as you can (I know, sounds a lot like Lavelle, but they really help!)

Ethan Laureano 3H

I would just say take your time and review your work once or twice. And if it is any consolation, the midterms and final will be multiple choice so if you do not see your answer, you know there may be a calculation mistake.

Ethan Laureano 3H

Because it is at constant volume. Normally, the change in internal energy would equal work plus q. However, since constant volume denotes no change in volume, work, or
-PdeltaV equals zero. Hope this makes sense.

Ethan Laureano 3H

Sadly it was a pretty disappointing game by the Chiefs. :(

Ethan Laureano 3H

Can someone explain the relationship between C_V and C_P. In Sapling, they say that C_P = C_V+R. However, other sources, including my TA's discussion say that it is C_P = C_V+nR. Can someone clarify this? Thank you.

Ethan Laureano 3H

Definitely need to focus on yourself holistically. Know that these 12-14 questions should not ruin your week!

Ethan Laureano 3H

When the equilibrium constant is smaller than 10^-4, then you can try. Of course, after trying, check to see if the x value is less than 5% of the initial concentration.

Ethan Laureano 3H

It helps to memorize the strong acids with this mnemonic: SO I BRought NO CLean CLOthes. Of course you'll also have to remember an additional CLO in HCLO₃

Ethan Laureano 3H

K refers to K_p

Ethan Laureano 3H

Descendants of the Sun

Ethan Laureano 3H

Heat is given off in the formation of bonds because energy is given off in the formation of bonds.

Ethan Laureano 3H

The temperature stays the same because the heat is used to break bonds and thus change phases.

Ethan Laureano 3H

A change in concentrations is considered a stress and the system will work to minimize this stress (add more products or reactants). Otherwise, equilibrium denotes unchanging concentrations.

Ethan Laureano 3H

Standard state of an element refers to the most stable phase at 1 ATM and the temperature of interest (usually 25 degrees Celsius).

Ethan Laureano 3H

So then what would be the difference between vaporization and evaporation? Are they one in the same or are there differences?

Ethan Laureano 3H

It is best to memorize as I think it is difficult to derive from knowing the qualifications. That being said, a weak acid will not lose hydrogen protons easily. Additionally, a weak acid will not result in a stable anion. And weak acids typically have short, strong bonds.

Ethan Laureano 3H

Basically, if Q is greater than K, that means that there are more products for Q than K (since products are at the numerator). According to Le Chatelier's principle, when a stress is applied to a system, the system works to counteract it. In this case, when there are more products, then the reaction...

Ethan Laureano 3H

Q is the products over reactants at any time of the reaction. If Q=K, then the reaction is at equilibrium. If not, you can determine where the reaction will go to (the products side or the reactants side).

Ethan Laureano 3H

It is best to think of it in terms of K_axK_b=K_w. A stronger acid means a higher K_a value. But, when looking at the aforementioned equation, a higher K_a means K_b will be lower.

Ethan Laureano 3H

I feel like you should find spaces where you can have fun. Once you do that, you can apply this mentality: "Work hard, play hard". I find myself grinding the week and then looking forward to zoom calls with friends or game nights. This way, I feel like I have earned it.

Ethan Laureano 3H

-Attend UA workshops -Go to study halls with chem 14b students -Figure out your strengths and weaknesses per unit and watch videos to strengthen those weaknesses -Peruse chemistry community (if you have a question it is likely that someone else has and posted that same question on chem community) -A...

Ethan Laureano 3H

Large K values are anything above 10^3 and small K values are anything below 10^-3

Ethan Laureano 3H

The reaction quotient tells us if the reaction is at equilibrium or not (if Q=K). If the reaction is not at equilibrium, the reaction quotient also tells us what side of the equation will the reaction work to form (reactants to products or products to reactants).

Ethan Laureano 3H

Like many have stated, changing pressure changes concentration because of the change in volume associated. However, not all changes to pressure result or is the result of a change in volume (i.e. adding an inert gas).

Ethan Laureano 3H

Le Chatelier's principle states that when a stress is applied to a system at equilibrium, the system would react to mitigate the stress. To visualize it more easily, think of an aquarium tank with a divider in the middle and both sides having equal water. If you fill more water on one side, the wate...

Ethan Laureano 3H

Bent and angular refer to the same molecular geometry (AX₂E, AX₂E₂)

Ethan Laureano 3H

You are right that CH₃F has a higher dipole moment. However, size and weight trump this. Since iodine is larger and heavier than fluorine (not to mention that there are three of them), the molecule will have stronger LDF and thus a higher melting point.

Ethan Laureano 3H

Salts of weak bases produce acidic solutions: When the salt NH 4 Br dissolves in water, it produces the cation (conjugate acid) NH 4 + and the anion (conjugate base) Br - . You have to look at the conjugate pair of the cation and anion. Looking at NH 4 + we know that it is derived from the WEAK BASE...

Ethan Laureano 3H

To memorize acids you'll just have to memorize (typically they'll have H in the front, but not always). The strong acids are HCl, HBr, HI, H₂SO₄, HNO₃, HClO₃, and HClO₄. For bases, it's a bit easier. Strong bases are group 1 and 2 hydroxides (OH) and oxides (O).

Ethan Laureano 3H

Hybridization is used to explain why carbon can form 4 bonds with the 4 hydrogen atoms while only having 2 unpaired electrons (from 2p). Since the normal convention states that covalent bonds will share one electron from each atom, then carbon needs to have four unpaired electrons. For this to happe...

Ethan Laureano 3H

If you remember, coordination compounds are neutral. With the knowledge that chlorine's charge is 1-, you can derive that the coordination complex (anything in brackets) is 1+. When you know that, then use your knowledge of the ligand charges to figure out the charge of the transition metal. In this...

Ethan Laureano 3H

I believe unhybridized orbitals arise when there are less regions of electron density than there are valence electrons of the element (but I am only theorizing based on one example: C). When Prof. Lavelle was lecturing about sp2, he used Carbon, an element with four valence electrons. Since there ar...

Ethan Laureano 3H

An important thing to know is that p=-log 10 . K A (the dissociation constant) is only really calculated for weak acids. That being said, the stronger K A is the stronger the acid is. In remembering that p=-log 10 , we can derive that pK A =-log 10 K A . In other words, when K A is larger, pK A is s...

Ethan Laureano 3H

My preferred method would be to determine the number of electron densities around the central atom and then figure out which ones are bonding pairs and which ones are lone pairs. This requires some memorization or visualization skills. For example, like someone mentioned before, this molecule has fi...

Ethan Laureano 3H

I believe you are correct.

Ethan Laureano 3H

You'll just have to memorize. In this case, this results in a square pyramid molecular shape which only has 90 degree bond angles.

Ethan Laureano 3H

When Lavelle mentions this in his lecture, he wants us to visualize a cation or an anion (something that produces an electrostatic potential) with the molecule who's polarity we are trying to figure out. When he says preferential attraction, he means which part of the molecule would most likely be a...

Ethan Laureano 3H

I believe resonance would be the only way delocalized pi bonds exist as resonance describes the delocalization of electrons.

Ethan Laureano 3H

Take a look at which is more electronegative. The more electronegative atom is the area which you can consider a negative pole. More specifically, if the net vector of these poles would be where the negative pole is.

Ethan Laureano 3H

Hybridization denotes a hybrid of two orbitals. When this occurs, the bonds that use the unpaired electrons in these hybrid orbitals are all of the same energy level. When you figure out hybridization orbitals used, you can figure out what types of bonds are used and consequently the properties of t...

Ethan Laureano 3H

AJForte-2C wrote:Do you need to create an afbau diagram in order to properly determine hybridization, or is it not necessary?

It helps to visualize but I don't think it is necessary. So long as you know the electron density regions and number of orbitals in subshells, you can figure it out.

Ethan Laureano 3H

When it comes to dipole-dipole, both molecules are polar with permanent dipole moments. With dipole-induce-dipole, one is a dipole while the other molecule is not naturally polar. It is only until the electrons of another molecule (in this case the polar one) influence the electrons of the non-polar...

Ethan Laureano 3H

You would think that because they are far then it'll be polar. However, when you search up an electronegativity chart, hydrogen is only about .35 less electronegative than carbon. Despite its position in the periodic table, hydrogen actually has a decent electronegativity.

Ethan Laureano 3H

You'll first determine if polar bonds form. You can figure this out by figuring out if the electronegativity difference between the two atoms is high enough to be considered polar bonds. Next, you will need to determine the net electric dipole moment. To figure this out requires knowing the magnitud...

Ethan Laureano 3H

Hi! There has to be a difference in electronegativity to have a polar bond. Further, there has to be an overall separation of charge, so the negatively charged molecules must be on one side. To add on to what Jessica said, if the polar bonds cancel each other (same magnitude and opposite vector dir...

Ethan Laureano 3H

It is polar because of the electronegativity difference between nitrogen and oxygen. As you may know, electronegativity is the tendency of an atom to attract electrons. Because oxygen has a higher electronegativity than nitrogen, and because the difference is large enough, electrons are closer to th...

Ethan Laureano 3H

Should we know how the molecular formulas when given the names of the molecule. For example, in Sapling there is a question where they ask to draw Lewis Structure of phosphate and phosphite ions as well as nitrate and nitrite ions. Should we know these molecular formulas off the top of our heads for...

Ethan Laureano 3H

Dipole-dipole is when two polar molecules (covalent molecules with unequal sharing of electrons) are attracted together due to electrostatic attraction between a negative and positive dipole. Ionic-dipole is when a cation or anion is attracted to the dipole (negative or positive area due to uneven e...

Ethan Laureano 3H

I'm not sure if this was put already but it is my favorite chemistry joke.

"If Iron Man and Silver Surfer teamed up, they'd be alloys."

Ethan Laureano 3H

Also how come Dr. Lavelle said that 4d state is lower energy than 5s state, after 2 e- have occupied 5s state. Based on what you said wouldn't it be the opposite? wouldn't it be that 4d state is lower energy than 5s state before 2 e- have occupied 5s state? When Lavelle says that 4s is lower than 5...

Ethan Laureano 3H

Sharon Kim 1A wrote:When writing the electron configurations, I understood it to be written as 3d orbitals before the 4s. Is that the same thing as saying 3d orbitals are filled before 4s?

No. That is purely a stylistic decision. It is the same as writing 4s 3d

Ethan Laureano 3H

From my understanding, electrons will always fill 4s before 3d. This is because 4s is slightly lower in energy than 3d. It is only when the 3d orbital is filled when 4s is greater in energy than 3d. For this reason, electrons are removed from 4s before 3d.

Ethan Laureano 3H

Do you mean isoelectronic atoms? If so, then it means having identical electron configurations. So Cl-, Ar, and K+ are all isoelectronic to one another. As for the other characteristics, it depends on whether the trend is affected by the nuclear charge or the atomic radius (how many orbitals). Sorry...

Ethan Laureano 3H

When Lavelle says this, he is referring to the unequal sharing of electrons. If you look at models (search up polar covalent bonds) depicting this, you can see electrons closer to one atom than the other. This results in a negative dipole.

Ethan Laureano 3H

Sadly it doesn't seem like Professor Lavelle updated his modules after the Heisenberg Uncertainty Principle one. He did say that if we enjoy them, he will be willing to create more.

Ethan Laureano 3H

hi! so if you notice on the periodic table, after atomic number 20, we encounter the transitional metals in the d-block. if you can recall from Dr. Lavelle's lectures, this transition to the d-block is significant because in contrast to what we would expect, where an increase in n, the energy level...

Ethan Laureano 3H

From my understanding of the lectures, elements greater than or equal to n=3 can have more than 8 electrons. This is because, when thinking about quantum numbers, you can only have l=2 if n is greater than or equal to 3 (l= 0,1... n-1). And when you have l=2, electrons can fill the d-orbital allowin...

Ethan Laureano 3H

For part a, l starts at 0 and can only go up to n-1. So this means a max of l=6. The values will be l= 0,1,2,3,4,5,6 (7 values). As for ml, it is the values of -l to l. In this case, the l value for d is 2. So the ml will be -2,-1,0,1,2. This corresponds with the 5 orbitals in the d subshell.

Ethan Laureano 3H

I believe those are the two main exceptions. I wouldn't know of any more, especially any others Professor Lavelle mentioned.

Ethan Laureano 3H

I think you are correct in your line of reasoning. It may be that the increased nuclear charge accounts for the size of the atomic radius more than the subshells of the valence electrons.

Ethan Laureano 3H

I think they are the groups (columns) 1 and 2 and 13-18. The rest are transition metals and inner transition metals (the two rows at the bottom). As for why they are called main group elements, I am not sure.

Ethan Laureano 3H

The ionization energy trend is based on how easy it is to remove the electron. Having a greater nuclear charge makes it harder to remove the electron. So, fluorine having a higher ionization energy than oxygen follows the trend. However, the exception can be seen in nitrogen, in which case nitrogen ...

Ethan Laureano 3H

I am pretty sure it is the second one. This is because longer wavelength equates to less energy, and the energy disparity between n=4 and n=2 is greater than from n=5 to n=1.

Ethan Laureano 3H

I usually write out the full number each time and then apply the sig figs at the end. That way, I can ensure I get the most accurate number.

Ethan Laureano 3H

That is just the value of the mass of an electron.

Ethan Laureano 3H

Well Lavelle did introduce the former so I would just stick to that.

Ethan Laureano 3H

In fact, this observation that increasing the intensity does not cause ejection of an electron proves that light has this duality of wave and particle. If light only acted as a wave, then increasing the intensity should have ejected the electron (just like how higher ocean waves have a higher knockb...

Ethan Laureano 3H

I believe that all objects have this wave-particle duality. The only reason we don't see it in objects like baseballs or cars is because the momentum of these objects results in a small wavelength (when plugged into the DeBriglie equation). This wavelength is too small for us to register that the ob...

Ethan Laureano 3H

Taylor K 2C wrote:I believe it is because kg is the fundamental SI unit for mass. But I'm not sure.

Yes. Kg are the standard SI units along with meters for length and seconds for time (to name a few more).

Ethan Laureano 3H

I liked the analogy Dr. Lavelle gave in his lecture. It is sort of like a cross country team. No matter how many members you have, if not one of them can jump the hurdle, the team is not going to win.

Ethan Laureano 3H

Professor Lavelle mentioned in the module pertaining to this topic that if you were to double the intensity (double the photons), then you would also double the electrons emitted. Thus, it can be seen in a 1:1 ratio, that is if the energy per photon is high enough.

Ethan Laureano 3H

Hello! From my understanding of the lectures, De Broglie's concept explain that any moving particle with a momentum has wave properties and so all matter has wave like properties. We only notice these properties in small objects with a high velocity since those with a higher mass (like the baseball...

Ethan Laureano 3H

20.01 has 4 sig figs. As for your base question, when there is a decimal point, all trailing zeros are counted in the sig fig count. However, when there is no decimal point, trailing zeros don't matter. Any zero in between numbers counts, regardless if there is a decimal. So 2001 will also be 4 sig ...

Ethan Laureano 3H

The problem tells us that a solution of CaCl2 in water forms a mixture that is 42.0% calcium chloride. It gives us the total grams of the solution (494.6 g) and asks what is the grams for water and calcium chloride. For the sake of the sig figs, I took into account the 42.0% and decided to round my ...

Ethan Laureano 3H

As everyone has stated above, round sig figs at the very end. This way, you prevent any inaccuracy by rounding per step. It may seem tedious to write out the full number every step, but it is needed to ensure accuracy.

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