CHEMISTRY COMMUNITY

Reina Robles 2B

Thank you so much!!

Reina Robles 2B

So I know that the format for the final has changed so it's a lot easier, but this topic is still super helpful to me. Thank you to everyone who posted here!

Reina Robles 2B

Congratulations!!!

Reina Robles 2B

Thank you so much, and best wishes to you!

Reina Robles 2B

Thank you!

Reina Robles 2B

Thank you!

Reina Robles 2B

Thank you!

Reina Robles 2B

Entropy is a state function, so the change in entropy of the system is the same regardless of whether the path is reversible or irreversible. I agree with the peer above's explanation. In addition, the initial & final states are the same because the process is isothermal, so, according to ΔS = ...

Reina Robles 2B

Standard potentials are given as reductions, not oxidations. Therefore, in the reduction of Fe2+, Fe2+ would be the reactant and Fe would be the product. In the given reaction, Fe2+ is being oxidized, which is why it's flipped and Fe2+ is the product rather than the reactant. But the standard poten...

Reina Robles 2B

In the textbook, the standard cell potential of this reaction

Fe(s) + 2Ag⁺(aq) → Fe²⁺(aq) + 2Ag(s)

is

E˚_cell=E˚(Ag⁺/Ag)-E˚(Fe²⁺/Fe)

Why is it product/reactant for Fe, and reactant/product for Ag?

Thanks!

Reina Robles 2B

Find the amount of heat transferred to ice in 0.5hrs using q=mCdeltaT. You will get 3135J transferred in 0.5 hrs. Then use dimensional analysis to find how many joules are transferred in 10hrs. You get 62.7kJ transferred in 10hrs. Then divide 62.7kJ by 8.33 moles and get 7.53kJ/mol for enthalpy of ...

Reina Robles 2B

In 1750, Joseph Black performed an experiment that eventually led to the discovery of enthalpies of fusion. He placed two samples of water, each of mass 150. g, at 0.00 8C (one ice and one liquid) in a room kept at a constant temperature of 5.00 8C. He then observed how long it took for each sample ...

Reina Robles 2B

Q: Calculate ΔS, ΔS surr , and ΔS tot for a) isothermal, reversible expansion and b) isothermal, free expansion of 1.00 mol of ideal gas molecules from 8.00 L to 20.00 L at 292 K. a) isothermal & reversible expansion: ΔS = +7.6 J/K ΔS surr = -7.6 J/K ΔS tot = 0 b) isothermal, free expansion (and...

Reina Robles 2B

Why is ∆U = 0 when ∆T = 0? Thanks!

Reina Robles 2B

I did this problem yet I keep getting my final answer as 28.6, which would round up to 29. The answer says it' supposed to be 28. Has anyone else been getting the same thing? I got that too, but when I used 2.8*10 -4 instead of 2.8274*10 -4 , I got 28.371, which rounds down to 28. Are we supposed t...

Reina Robles 2B

You do use w = P * A * D! w = 2 atm * (0.015 m) 2 * 0.2 m * pi w = 2.8274 * 10 -4 m 3 * atm Then, you can multiply the answer by 101,325 Pa to convert from atm to Pa. Once you have your answer in m 3 * Pa, it is equal to that amount in joules (J). Where did you get 0.015m from and pi from? I believ...

Reina Robles 2B

I'm getting almost all of the answers wrong for these two questions and I'm not sure why. Any help is appreciated, thanks! 4E.5 a) 3C 2 H 2 (g) --> C 6 H 6 (g) What I did: [3(837)] + [6(-348)] = 423 kJ.mol -1 Textbook answer: -587 kJ.mol -1 4E.7 a) N 2 (g) + 3F 2 (g) --> 2NF 3 (g) [944+(3*158)] + [6...

Reina Robles 2B

I have the solutions manual and can also confirm that it's correct!

Reina Robles 2B

You don't need K nor the ICE table because Ba(OH)2 is a strong base and thus will be 100% dissociated in water. This means you can assume the equilibrium concentration of the reaction will be: [Ba2+]final = [Ba(OH)2]initial = 0.025M and [OH-]final = 2*[Ba2+]final = 0.05M Remember that these conclus...

Reina Robles 2B

"6A.23 Calculate the molar concentration of Ba(OH)2(aq) and the molar concentrations of Ba21, OH2, and H3O1 in an aqueous solution that contains 0.43 g of Ba(OH)2 in 0.100 L of solution."

Are we supposed to use the ice box method to solve this? K wasn't given.

Thanks!

Reina Robles 2B

5G.1 asks to "State whether the following statements are true or false. If false, explain why." For Part D of the question, it says "If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger." Why is that marked as true w...

Reina Robles 2B

Test anxiety is a big issue for me and I'd like to thank everyone who gave tips! Here are some of mine (sorry for any repeats): 1. Exercise! Or at least, get moving. I can get incredibly tense while studying, and working out helps relieve that. Keeping your body healthy in general is also helpful in...

Reina Robles 2B

If you mean hydrogen bonding, then it's where nitrogen, oxygen, and fluorine atoms with a lone pair are bonding sites (each lone pair is one bonding site). Hydrogen atoms attached to a nitrogen, oxygen, or fluorine are also bonding sites.

I hope this helps!

Reina Robles 2B

Yes, all molecules have LDF. Induced-dipole dipole occurs between a polar molecule and a non-polar molecule.

I hope this helps!

Reina Robles 2B

Nitrogen, oxygen, and fluorine atoms with a lone pair are bonding sites (each lone pair is one bonding site). Hydrogen atoms attached to a nitrogen, oxygen, or fluorine are also bonding sites.

I hope this helps!

Reina Robles 2B

Unless all the atoms are the same, tetrahedrals are always polar. CH2F2 looks flat on paper, but its 3D structure shows that it's not.

I hope this helps!

Reina Robles 2B

You use those when the ligand already contains a prefix (for example, (en)), is a polydentate, or it starts with a vowel.

I hope this helps!

Reina Robles 2B

It's probably simpler to delete the old post and repost it here.

Reina Robles 2B

Not that I know of, but it might be better to not make posts back to back.

Reina Robles 2B

Substances with higher boiling points will have stronger intermolecular interactions. Conversely, substances with lower boiling points will have weaker intermolecular interactions.

I hope this helps!

Reina Robles 2B

I believe that you can still look at posts (since you don't have to login for that) but you can't reply or make your own unless you're going to have Dr. Lavelle for Chem 14B. In that case, you will be able to post.

Reina Robles 2B

Are you talking about ammine for the neutral lignad: NH3 and about their spelling? If so, I was told in one of my plf's that the spelling matters in regards to points so when naming coordination compounds make sure you write ammine with double m's! There is a difference between an amine and an ammi...

Reina Robles 2B

Thank you both! I am pretty sure the only givens are those we have seen on the midterm and tests. You may be able to ask about abbreviations as long as they are not on the periodic table/have been explained in class. It would be best to memorize ion charges, but worst case you can calculate the form...

Reina Robles 2B

Thank you both!

Reina Robles 2B

A ligand is polydentate if when we draw the lewis structure there is more than one bonding site in the form of lone pairs present on separate atoms in the compound. Fro the textbook, the main ones we have to know are en which is bidentate, bien which is tridentate, oxalate which is bidentate, and e...

Reina Robles 2B

Polydentate ligands have more than one lone pair that it can donate. They are also usually in the structure of atom with a lone pair — space atom — space atom — atom with a lone pair.

Reina Robles 2B

How do you write the hybridization of pi bonds?

Reina Robles 2B

How do I know if a ligand is polydentate? Thanks!

Reina Robles 2B

So I know polydentate ligands have multiple sites where they can bond to the same transition metal, but how do you know that it can do that? Thanks.

Reina Robles 2B

During the final, will we be given any information for naming coordinate compounds? (ex: what abbreviations would mean, ion charges, etc.)

Reina Robles 2B

Is there a difference between amine and ammine?

Reina Robles 2B

A base and a Lewis base are the same thing. Lewis base just states how Lewis describes bases (donating an electron).

Reina Robles 2B

Acids have a pH lower than 7, and they produce hydronium (H3O+) when they react with water. The Lewis definition of an acid states that it accepts an electron; the Bronsted definition states that it donates a proton. Bases have a pH higher than 7, and they produce hydroxide (OH-) when they react wit...

Reina Robles 2B

The dipole moments cancel out when they're facing in opposite directions. If there's a diagonal dipole, I like to break them up into the two directions it's made of (up-right, down-right, etc.) and then check if any of the other dipoles cancel it out.

I hope this helps!

Reina Robles 2B

Normally, electron acceptors (Lewis acids) are positively charged, and electron donors (Lewis bases) are negatively charged (this may not be the case all the time). For me, drawing the Lewis structure helps determine which species has lone pairs of electrons, which helps to determine the Lewis base...

Reina Robles 2B

Yes, if the intermolecular forces between two molecules is stronger, it will be harder to break the bonds between them. The strengths of the different types of intermolecular forces in increasing order are as follows: induced dipole-induced dipole (London forces) < dipole-dipole < ion-dipole < ion-...

Reina Robles 2B

So I know Lewis acids are electron acceptors, and Lewis bases are electron donors. But how do you know whether a molecule accepts or donates an electron?

Reina Robles 2B

I believe so. Just as a side note though, the molecules aren’t bonded to each other like in a covalent or ionic bond. They’re interacting with each other/strongly attracted to each other.

I hope this helps!

Reina Robles 2B

Yep, promotion means that an electron goes to a higher energy orbital. However, the orbital must be empty. So while carbon can promote an electron, nitrogen can’t (none of its p orbitals are empty).

I hope this helps!

Reina Robles 2B

-ate is for negatively charged complexes. Usually complexes are neutral or positively charged, so -ate is supposed to be a red flag/signifier.

Reina Robles 2B

Hi, I'm a little confused. Are all the bond angles in square pyramidal (AX5E) 90 degrees? What about the bond angle between the two equatorial atoms? And doesn't the lone pair also affect the angle? And with t-shaped (AX3E2, AX3E3), are the bond angles 120 and 90 degrees even though there are lone p...

Reina Robles 2B

Hi Tony! The link didn't work when I tried it, but I did use it to find this one: https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_A_Molecular_Approach_(Tro)/10%3A_Chemical_Bonding_II%3A_Molecular_Shapes%2C_Valance_Bond_Theory%2C_and_Molecular_Orbital_Theory/10.3%3A_VSPER_Theory%3A_T...

Reina Robles 2B

Haley Fredricks 1B wrote:Technically, yes, but in reality it more has to do with the formal charge. Whatever makes it the lowest is how many the octet should be expanded to.

I completely forgot about that. Thank you!

Reina Robles 2B

For atoms with expanded octets, the amount they can expand to is limited to what shell they're in, right?

For example, Si has valence electrons in the 3p shell and can expand to fill the 3d shell but not beyond that.

Reina Robles 2B

On the midterm, would we have to know how to write the molecular formula if we're given the chemical name? If so, how can I do that?

Thanks!

Reina Robles 2B

I definitely agree with all the advice here! Also, I talked to my TA about this, and he suggested using the Cornell note-taking system (although it might be too late to do that now). Here's a way you can do it if you don't know how to already: https://upload.wikimedia.org/wikipedia/commons/4/4f/Note...

Reina Robles 2B

The answer is C.

Reina Robles 2B

They don’t need eight electrons to fill their shell. H and He only have the 1s shell, which only needs 2 electrons to fill it. Li and Be only have the 1s and 2s shell, and the 2s shell only needs two electrons to fill it.

Hope this helps!

Reina Robles 2B

In chemistry, penetration means an electron's probability density near the atom's nucleus. In other words, how close an electron can get to the nucleus. s-electrons of any shell can be close to the nucleus/have greater penetration, while the electrons of other subshells (p, d, etc.) have less penetr...

Reina Robles 2B

n is the shell, l is the subshell, m_l is the orbital, and m_s is the electron's spin. I hope this helps!

Reina Robles 2B

Velocity: meters per second Threshold energy: Joules Plank's constant: Joules times seconds Frequency: Hz (which is also cycles per second) You can also find these on the constants and equations sheet that they give us during tests: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14A/c...

Reina Robles 2B

I didn't take calculus in high school and I don't remember a lot from pre-calculus, is there anything I should review/learn about for this class? Thanks!

Reina Robles 2B

The De Broglie wavelength equation is used to see if a moving particle has detectable wavelike properties.

Reina Robles 2B

In the photoelectric experiment, increasing the intensity would only increase the number of photons (like making a light brighter, for example). On the other hand, the researches needed to increase the energy of each individual photon. This is done by increasing the frequency of the EM wave.

Reina Robles 2B

Is saltwater a mixture or a compound? From what I remember, the textbook says one thing while the internet says another. Thanks!

Reina Robles 2B

Are orbitals the same as lobes? In the textbook and lecture an atom's structure is usually described as shell --> subshell --> orbital, but where do lobes fit into this? Thanks.

Reina Robles 2B

I read that the number of subshells in an atom's shell corresponds to the principal quantum number, but is there a pattern to how many orbitals are in each subshell? Thanks!

Reina Robles 2B

I never really self-studied before and was wondering if anyone could explain to me how they plan to study for this class/any study tips in general? Thanks!

Reina Robles 2B

Hi, I'm not sure if this question has been answered already, but will we be able to bring our own copy of the periodic table to the test? Thanks.

Reina Robles 2B

Thank you for the advice! Best wishes in medical school and beyond.

Reina Robles 2B

Thanks for all the information everyone! Also I think this is the link for the SI info that was mentioned earlier:

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

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