CHEMISTRY COMMUNITY

Alice Chang 2H

Is anyone having a hard time figuring out how to do Endgame 3B?? I can balance the oxidation reaction, but I can't figure out how to do the reduction reaction with Br2. Hi y'all, it's me again with a mental breakdown over this problem. Make sure to balance your half reactions correctly with the rig...

Alice Chang 2H

Is anyone having a hard time figuring out how to do Endgame 3B?? I can balance the oxidation reaction, but I can't figure out how to do the reduction reaction with Br2.

Alice Chang 2H

Hi nevermind but leaving this here in case someone else is having trouble too.

I forgot to add a negative sign before I simplified further than lnQ.

I'm losing my mind.

Alice Chang 2H

Is anyone else having trouble calculating the concentration of Fe2+ in Endgame 2D?

I have all the right numbers for each variable (checked on the answer key), and I'm using Nernst Equation, but every time I somehow manage to calculate wrong??

Please help I feel like I'm about to lose my mind.

Alice Chang 2H

Does anyone know if the take home final will be turned in online or in person? I'm trying to make plans to go back home :(

Alice Chang 2H

I'm not sure if these sites help, but here: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Chemical_Equilibria/Principles_of_Chemical_Equilibria/Kinetically_vs_Thermodynamically_Stable Summ...

Alice Chang 2H

In case you didn't see, Professor Lavelle just dropped a PDF on rate laws. I think it's safe to assume we should know the basic idea behind how rate laws are derived and what they're used for. https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Kinetics_Integrated_Rate_Laws_Examples.pdf

Alice Chang 2H

According to this site: https://courses.lumenlearning.com/boundless-chemistry/chapter/the-rate-law-concentration-and-time/ The rate law for a chemical reaction is an equation that relates the reaction rate with the concentrations or partial pressures of the reactants. So, I think it's because rate l...

Alice Chang 2H

Title, but what is the purpose of it??
What are the equations used to derive it used for?

Alice Chang 2H

In a first order reaction, there will be one reactant present in the rate law. For a second order reaction, you can either have a rate law with one reactant to the second order, or with two reactants both to the first order. Found this answer (and others) here: https://lavelle.chem.ucla.edu/forum/v...

Alice Chang 2H

I had a TON of trouble with this one too!

I eventually gave up and assumed the textbook made a mistake and flipped the entire cell diagram around. Or, we were supposed to flip the cell diagram ourselves (?) since we were asked for E(M2+/M) rather than E(M/M2+).

Alice Chang 2H

I'm not sure if this will help much, but this website breaks it down a bit. Give it a read? https://chem.libretexts.org/Courses/University_of_California_Davis/UCD_Chem_002CH/Text/UNIT_II%3A_ELECTRO-CHEMISTRY/17.3%3A_Concentration_Effects_and_the_Nernst_Equation#The_Effect_of_Concentration_on_Cell_Po...

Alice Chang 2H

Asha Agarwal 1E wrote:The units will just be in kJ since the units in n and F cancel in terms of moles.

I thought ∆G was in units of kJ since the textbook omits the assumed "/mol" part. A TA mentioned this to me as well in a previous topic. Was I wrong this whole time?

Alice Chang 2H

They're actually assuming that you know the units for ∆G to be kJ/mol. A lot of times, the textbook omits the "/mol" part because it is assumed to be included.

Alice Chang 2H

The only difference between ∆G and ∆G° is that ∆G measures free energy for any conditions not standard while ∆G° measures free energy for standard conditions (1 atm and 25 degrees Celsius).

So yes, the same rules apply with the negative and positive ∆G and ∆G°.

Alice Chang 2H

An example of some half reactions would be: Zn(s) --> Zn2+(aq) Cu2+(aq) --> Cu (s) So in these examples, which one is oxidizing and which one is reducing? Since Zn is becoming more positive, it is being oxidized (losing electrons). Since Cu2+ becomes more negative, it is being reduced (gaining elec...

Alice Chang 2H

Is there any difference in the process to balance a reaction when it's either acidic or basic?

Alice Chang 2H

Shimei_2F wrote:Our TA said that there's a system that automatically checks your chemistry community posts.

I heard this too, and that Prof. Lavelle also personally checks sometimes since he's always somehow online LOL

Alice Chang 2H

Copied from this site: http://www.scramlinged.com/resources/Notes+on+Voltaic+Cells.pdf Qualitatively, the effect of concentration of cell potential follows Le Chatelier's Principle. If the concentration of the reactants in the equlibrium constant expression increases, that pushes the reaction in the...

Alice Chang 2H

I think it's similar to the concepts of Le Chatelier's Principles.

This website talks a bit about it with a worked example: https://www.mikeblaber.org/oldwine/chm1046/notes/Electro/Conc/Conc.htm

Alice Chang 2H

For transition metals, use the oxidation numbers from other elements in the compound to find the oxidation number of the metal by subtracting from the overall charge on the compound. That was a bad explanation but this website breaks it down really well: https://socratic.org/questions/how-do-you-cal...

Alice Chang 2H

I believe it's usually assumed that people know it's kJ/mol, and the mol is just omitted. I think my TA mentioned that once during discussion, but my memory is fuzzy...

Alice Chang 2H

I think they may be referring to the same thing. In the textbook, I believe they were used interchangeably.

Alice Chang 2H

I thought the standard unit for temperature was Kelvin, so I'm not sure about it being interchangeable.

Alice Chang 2H

It's best if you look at it visually, and try to imagine it rotate as a 3-d model. For cis-, there are 12 orientations. It helped me a lot to focus on the red dots (forgot what element they represented), and try to rotate them to different positions (1 on top and 1 on side, 1 on bottom and 1 on side...

Alice Chang 2H

According to the textbook, the cis compound has 12 different orientations while the trans compound only has three different orientations, decreasing the entropy due to the fact that there is less uncertainty in its orientations. In regards to entropy, residual entropy is the measure of how many dif...

Alice Chang 2H

You might be asked to find entropy of a system given information about the system. So, this may include terminology like this.

BTW,
Isobaric: pressure remains constant

Isochoric: volume remains constant

Isothermic: temperature remains constant/the same

Alice Chang 2H

Internal energy (ΔU): the total energy of a closed system. Internal energy is the sum of potential energy of the system and the system's kinetic energy thermal energy: the internal energy of an object due to the kinetic energy of its atoms and/or molecules (raise in temperature leads to an increase ...

Alice Chang 2H

I think energy density is always positive, since the definition of energy density is "the amount of energy stored in a given system or region of space per unit volume."

I don't think energy can be negative (but I may be wrong), so energy density can't be negative.

Alice Chang 2H

ΔS : change in entropy q(rev) : heat inputted into the system that is reversible T : temperature This equation is a "basic way of evaluating ΔS for constant-temperature processes such as phase changes, or the isothermal expansion of a gas." So by dividing heat inputted into the system by t...

Alice Chang 2H

I'm probably wrong about this, but I think reversible reactions can have constant pressure. But according to Le Chatelier's, a change in pressure will cause the reaction to want to stabilize to accommodate for the new pressure. I read somewhere that the q(rev) is usually substituted as the amount of...

Alice Chang 2H

What is the relevance of knowing phase changes? Like, how are they used in calculations?

Alice Chang 2H

So I wrote in my notes under the title "degeneracy" that:
thermodynamic property: small error in S
statistical: large error in W

Can anyone help me decipher what that means? LOL tysm

Alice Chang 2H

Will we be told the specific system/is it provided in the problem, or are we supposed to figure it out on our own?

Also, are there different equations/things to know per system?

Alice Chang 2H

Are there different types of calorimeters? What were the basic ideas behind the experiments that use these types of calorimeters?

Alice Chang 2H

Is there a difference between state property vs state function?
I remember both being used in lecture, but are they the same thing/concept?

Alice Chang 2H

I got this from https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/07%3A_Thermochemistry/7.8%3A_Standard_Enthalpies_of_Formation For example, although oxygen can exist as ozone (O3), atomic oxygen (O), and molecular oxygen (O2), O2 is the most stable...

Alice Chang 2H

https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/enthalpy-chemistry-sal/v/hess-s-law-example

I'm not sure if this will help clarify things, but this is a worked example from Khan Academy using Hess's Law if you learn more visually.

Alice Chang 2H

https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/enthalpy-chemistry-sal/v/hess-s-law-example

Khan Academy pulling through with a worked example! If you're more of a visual learner, this might help.

Alice Chang 2H

What exactly is a state property? I wrote it was a value determined by its current state, but I'm not sure what that means. Does it mean like the amount of energy being carried while in that state (e.g., liquid, solid, gas, etc.)?

Alice Chang 2H

I'm having a bit of trouble trying to figure problem 5J.13 out. I'm trying to work backwards with the given answer for this question, but I'm still getting stuck. In the problem, the concentration can be worked out, and the temperature is given, so the partial pressures (?) of each molecule can be w...

Alice Chang 2H

If it helps, Khan Academy has a video on Le Chatelier's Principle here: https://www.khanacademy.org/science/chemistry/chemical-equilibrium/factors-that-affect-chemical-equilibrium/v/le-chatelier-s-principle

Alice Chang 2H

If you're more of a visual learner, Khan Academy has a video explaining Le Chatelier's Principle here: https://www.khanacademy.org/science/chemistry/chemical-equilibrium/factors-that-affect-chemical-equilibrium/v/le-chatelier-s-principle

Alice Chang 2H

Like everyone else said, do all the homework questions, but do it to clarify any questions that you may have on a topic, not for completion.
I found Lyndon's workshops and review sessions (especially before the midterm and final) to be the most helpful out of all the available resources!

Alice Chang 2H

If your pOH value has 3 sig figs (counted after the decimal!), you use that to calculate your pH by subtracting from 14.000 (has 3 sig figs as well)
There's a worksheet on the chem 14B website that explains sig figs further if you need more help :)

Alice Chang 2H

If you would like to learn more about the specific factors that could affect equilibrium, this website lists the effect of different changes in concentration, temperature, and pressure: https://www.chemguide.co.uk/physical/equilibria/lechatelier.html

Alice Chang 2H

ICE tables are helpful when given limited information, like when the initial concentration and equilibrium constant is given. ICE tables help you find the concentration at equilibrium by organizing your given information in a neat little way so you can find each concentration at equilibrium through ...

Alice Chang 2H

I thought this site helped a bit to explain: https://chemistry.stackexchange.com/questions/18567/what-would-be-the-effect-of-the-addition-of-an-inert-gas-to-a-reaction-at-equili

Basically, inert gasses only affect equilibrium if the volume changes.

Alice Chang 2H

When a reaction is at equilibrium, both sides of the equation (reactants and products) will be reacting, but at the same rate (thus being equal). If you find that K is equal to 1, then the reaction is at equilibrium. Solving for Q means solving for the ratio between products and reaction at any time...

Alice Chang 2H

I think the process is going to be the same in order to find equilibrium concentrations (i.e., solving for X), but if it makes more sense to you to not use an organized table then that works too.

Alice Chang 2H

Basically Kc is the equilibrium constant when it is found through the use of concentrations (typically non-gasses), while Kp is the equilibrium constant when it is found through the use of partial pressures (typically gasses).

Alice Chang 2H

I think this is the full list:
Strong acids:
HCl, HBr, HI, HNO3,H2SO4, HClO4
Strong bases:
NaOH, CaO, KOH, Na2O, Ba(OH)2

If you know the strong acids and bases, the weak ones should be easy to figure out :)

Alice Chang 2H

C10H16N2O8 with a -4 charge!

Alice Chang 2H

I think it has something to do with the orientation of the bonds, how pi bonds are side-by-side and can't rotate while sigma bonds are end-to-end and allow for rotation. Since sigma bonds are end-to-end, they can be hybridized since orbitals can overlap, while there is no overlap with pi bonds.

Alice Chang 2H

I think this is the full list:
Strong acids:
HCl, HBr, HI, HNO3,H2SO4, HClO4
Strong bases:
NaOH, CaO, KOH, Na2O, Ba(OH)2

If you know the strong acids and bases, the weak ones should be easy to figure out :)

Alice Chang 2H

Yes, I believe so! In one of Lyndon's Marshmallow problems, the positive charge of K affected the oxidation number of the metal in the bracket:

K2[Ni(CN)4] -> potassium tetracyanonickelate (2)

Alice Chang 2H

This site helps a bit to explain the process! : https://chem.libretexts.org/Courses/Sacramento_City_College/SCC%3A_Chem_420_-_Organic_Chemistry_I/Text/01%3A_Introduction_and_Review/1.15%3A_Predicting_Relative_Acidity

Alice Chang 2H

This site helps to explain sigma and pi bonds and their formation with visuals! : https://brilliant.org/wiki/sigma-and-pi-bonds/
Helps to explain why pi bonds break and sigma bonds allow for rotation :)

Alice Chang 2H

According to google it's "a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points."

Idk if that helped at all haha
"
:

Alice Chang 2H

According to this website at https://employees.csbsju.edu/cschaller/Reactivity/mechreview/UMintermed.htm , The larger the atom, and the further the electrons from the nucleus, the more polarizable it is. The more polarizable the atom, the more stable the anion. Within a row of the periodic table, th...

Alice Chang 2H

Using the generic trends of the periodic table, the more electronegative atoms are found in the upper right hand corner of the table.

So I assume with these compounds you just compare the atoms individually to figure out which is more electronegative?

Alice Chang 2H

This site gives a bit more information on how to find oxidation states!
https://sciencing.com/transition-metals-unique-6302350.html

Hope this helps :)

Alice Chang 2H

I think this site helps summarize it fairly well: https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch12/complex.php They said: According to this model, transition-metal ions form coordination complexes because they have empty valence-shell orbitals that can accept pairs of electrons from a Lewi...

Alice Chang 2H

This video helped a bit in explaining the concept of orbital overlap: https://www.youtube.com/watch?v=ppR2Zjtgrsk But, basically the idea is bonds are formed through valence electrons, but not all valence electrons are from the same orbital (when combining 2 largely different atoms). So, when these ...

Alice Chang 2H

It should be, since the idea of sigma and pi bonds are based on the number of bonds created between atoms. Since resonance structures are just different structures of the same compound with electrons rearranged, then the same rules for deciding sigma and pi bonds should be the same, or at least I'm ...

Alice Chang 2H

I found that this answer gives a nice visual representation of how atoms can rotate around with a sigma bond, check it out!

https://chemistry.stackexchange.com/questions/68480/why-can-a-sigma-bond-rotate

Alice Chang 2H

My TA told us that we should try to memorize them all in case they appear on the test. He suggested to make flash cards for them and practice as much as we can.

Alice Chang 2H

This website helped a bit if you want to check it out: https://chemistry.stackexchange.com/questions/2426/why-do-single-double-and-triple-bonds-repel-each-other-equal-amounts To summarize, in VSEPR theory, multiple bonds give deviations from the normal ideal shape with just single bonds.

Alice Chang 2H

I found this website super helpful! https://chemistry.stackexchange.com/questions/4399/how-do-i-figure-out-the-hybridization-of-a-particular-atom-in-a-molecule Based on the number of atoms bonded to the central atom and the number of lone pairs, the hybridization can be sp^3 if 4, sp^2 if 3, sp if 2...

Alice Chang 2H

Elements with a d-orbital can allow for more than 8 electrons/break the octet rule! Xenon has a d-orbital so it can hold more electrons.

Alice Chang 2H

"A dipole-induced dipole attraction is a weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar species." Got it here: https://www.chem.purdue.edu/gchelp/liquids/inddip.html Hope it...

Alice Chang 2H

Yes, shape affects the strength of the interaction. This sounds like a dumb comparison, but the way that I saw it was if I had 2 sets of magnets: - 1 set is two flat bar magnets - 1 set is two sphere magnets like marbles If I played around with these magnets, it would be much more difficult to separ...

Alice Chang 2H

505106414 wrote:Is it okay to break the octet rule in order to minimize formal charge?

only if the atom is able to take less or more than 8.
For example, Hydrogen only takes 2 electrons, while any element with a 3d-orbital or after can take extra electrons (more than 8).

Alice Chang 2H

I found this website to be pretty useful as they include models too: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Dipole_Moments

Alice Chang 2H

The trend is towards the bottom left is increasing atomic radius, right? Basically the way that I think of it, on the top right of the periodic table, the elements have less electrons to shield the outer electrons, so the protons in the nucleus have a stronger pull. Meanwhile, on the bottom left, th...

Alice Chang 2H

m = -l to +l

Also, remember if l=0, then m=0 too since it is -0 to +0.

Alice Chang 2H

Honestly didn't know this was a thing until now, but I learned some really cool info from this site and it helped a lot!
Hope it helps too.
https://www.majordifferences.com/2014/10/difference-between-sigma-and-pi-bond.html

Alice Chang 2H

It's a lot, but you can find a good explanation here: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/Deriving_the_de_Broglie_Wavelength ...

Alice Chang 2H

Ooh boy, if you want the long version, you can find the answer here on https://www.quora.com/Why-is-h-divided-by-4pi-in-the-uncertainty-principle or here https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)...

Alice Chang 2H

The way that I understand it is that in electron configuration, you arrange by increasing energy. So, in this case, if only the s-shell is filled, then the s-shell is named first. But otherwise, if there is an electron in the d-shell, then the d-shell is named first before s-shell, because the d-she...

Alice Chang 2H

One of the UA's explained this during the 5-8 PM session on Friday: If I recall correctly, the idea is that you should be writing electron configurations in the arrangement of increasing energy. The d-orbital has less energy when an electron is placed in the d-orbital, but otherwise, the s-orbital h...

Alice Chang 2H

Found out through a Google search that covalent bonds can be both polar and nonpolar! Nonpolar covalent bonds are a type of chemical bond where two atoms share a pair of electrons with each other. Polar covalent bonding is a type of chemical bond where a pair of electrons is unequally shared between...

Alice Chang 2H

Hey according to the website https://chem.libretexts.org/Courses/University_of_Illinois%2C_Springfield/UIS%3A_CHE_267_-_Organic_Chemistry_I_(Morsch)/Chapters/Chapter_01%3A_Structure_and_Bonding/1.03%3A_Lewis_Structures : The central atom is usually the least electronegative element in the molecule o...

Alice Chang 2H

According to the website here at https://wiki.ubc.ca/Effective_Nuclear_Charge_-_Definition_and_Trends : The periodic table tendency for effective nuclear charge: Increase across a period (due to increasing nuclear charge with no accompanying increase in shielding effect). Decrease down a group (alth...

Alice Chang 2H

Hey I found this answer here at https://www.brightstorm.com/science/chemistry/the-atom/exceptions-to-electron-configuration/ : There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially fill...

Alice Chang 2H

According to this website ( https://www.sparknotes.com/chemistry/organic1/covalentbonding/terms/ ): Resonance stabilization - Because resonance allows for delocalization, in which the overall energy of a molecule is lowered since its electrons occupy a greater volume, molecules that experience reson...

Alice Chang 2H

I believe it means energy level, but this video explains it a bit better visually:

https://www.youtube.com/watch?v=VQJx6JAq_po

Alice Chang 2H

Here's some info I found by a Google search online here: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Electronic_Structure_of_Atoms_and_Molecules/Electronic_Configurations/Aufbau_Principle Aufbau co...

Alice Chang 2H

Someone asked a similar question earlier, here's a link to the thread:
https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=31218

Hope it helps!

Alice Chang 2H

Some people have asked a similar question in the past on this site, so you can find the answer here: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=30918 I also found it described on this website: http://eilat.sci.brooklyn.cuny.edu/cis1_5/old%20hws/hw2d_c.htm The Lyman series involve jumps to o...

Alice Chang 2H

Honestly a little confused on to what you're specifically asking, but I found this online that defines the p-orbital and its configuration numbers: The magnetic quantum number, ml, represents the orbitals of a given subshell. For a given l, ml can range from -l to +l. A p subshell (l=1), for instanc...

Alice Chang 2H

I found this info from a quick Google search, so you may want to double check this info. But here's what I found: Rydberg equation: The Rydberg formula is a mathematical formula used to predict the wavelength of light resulting from an electron moving between energy levels of an atom. De Broglie equ...

Alice Chang 2H

Speed in a vacuum is defined as c= 3.00*10^8 m/s, which is a constant while measuring other speeds/variables in the electromagnetic spectrum topic. A formula given from the lecture is c=\lambda \times v , which is (the speed of light) = (wavelength) x (frequency). You can use the speed of light, a c...

Alice Chang 2H

Not sure if someone has already asked this, but I was wondering what diffraction actually is? I looked at the definition which basically defined it as waves that come out of a narrow aperture after a light passes through. But what is diffraction useful for? Is it measurable and we can use it to find...

Alice Chang 2H

I'm not sure if this is the correct topic to post this under, but can anyone help me understand question 1A.11? I read through the answer from the solutions manual, but I don't understand how they got to that conclusion. Here's the question: In the spectrum of atomic hydrogen, several lines are gene...

Alice Chang 2H

Not sure if this is right, but from what I've found online, electrons can only move about 1% of the speed of light. The question's answer is around 4.12 x 10^16 m/s for the electron's speed, which is way faster than light (assuming I did the calculations correctly). So, I assume that this is unreaso...

Alice Chang 2H

I searched this up online, not sure if it's true but it seems logical: It’s a stepping stone in finding the molecular formula of an unknown compound. You can find the empirical formula experimentally, then get some more information from Nuclear Magnetic resonance imaging/ spectroscopy etc, and then ...

Alice Chang 2H

TIL: I just found this online, hope this helps! There's something called Hill System. This is the system of writing chemical formulas. In this system the carbon atoms are first, then hydrogen atoms and then other in alphabetical order. When the formula contains no carbon or hydrogen atoms, then all ...

Alice Chang 2H

I'm not sure if this is just me being dumb and not getting it or not, but I searched up the rules for sig figs and found the basic rules for multiplication and division, which states that after the process of * or /, the least amount of sig figs throughout the entire process determines how many sig ...

Alice Chang 2H

This is something I found while looking up rules for sig figs, hope this helps: For addition and subtraction use the following rules: 1. Count the number of significant figures in the decimal portion ONLY of each number in the problem 2. Add or subtract in the normal fashion 3. Your final answer may...

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