CHEMISTRY COMMUNITY

Gina Spagarino 3G

If we haven't used it in any assigned problems hopefully it won't be needed on the final??

Gina Spagarino 3G

Hi! I'm not positive my logic is correct, but from my understanding-- it does not necessarily have to be a porous disk because of the salt bridge. The electrolytes form from the cathode to the anode in this salt bridge, with the negative electrolyte coming from the reaction in the cathode the result...

Gina Spagarino 3G

Yes, and this relationship is important for the pre-equilibrium method in determining a rate law with a fast then slow step.

Gina Spagarino 3G

Galvanic cells have the flow of electrodes from anode to cathode without adding an electrical current. In a concentration cell, there is the same aqueous solution in different concentrations, with the cathode containing the higher concentration, and I believe it is a type of Galvanic cell as mention...

Gina Spagarino 3G

Hi, that is the K of the fast step 1, to use the pre-equiliibrium approach to substitute in for step 2 the slow step. It is set up for step 1 as [products]/[reactants], as K usually is... because K also equals k/k', then solving for [HClO-] allows it to be substituted out of step 2 since it is an in...

Gina Spagarino 3G

Even if the proposed rate law fits the criteria of the sum of the elementary steps = the overall reaction, and the mechanism agreeing with the experimentally determined rate law, the reaction mechanism is not proved correct, only showing it is a possibility. The actual determining is beyond what we ...

Gina Spagarino 3G

Like everyone said above, the rate determining step is the slow step. Lecture #24 also includes a diagram that shows that the rate determining, slow, step has a higher energy barrier than the fast step.The rate law for the overall reaction is the rate law of the slowest step.

Gina Spagarino 3G

First add H₂O as appropriate to balance the oxygen, then add H⁺ to the opposite side because of the hydrogen in the water molecules. Then, if it is a basic solution, add OH- to both sides to balance the added H+.

Gina Spagarino 3G

Taking 20 minutes for a yoga flow is quite worth the time I think!. Also, CBD (with no THC!!) eases my anxiety

Gina Spagarino 3G

I like to remember that anode contains the solution that loses an electron using the phrase An Ox, as well as Dr. Lavelle's LEO [lose electron oxidation]. Both are animals which is nice. In a redox reaction, reduction an oxidation must both occur, so lose electron solution=anode, and the reaction in...

Gina Spagarino 3G

I like handwritten notes and highly recommend an iPad (or any tablet) for them. It keeps notes organized and they are easy to edit, like u can write something and then relocate the chunk you just wrote, which is not possible on paper. I like Notability a lot and it is very nice to be able to have al...

Gina Spagarino 3G

I am hoping to surf and go to the beach a lot, but that is definitely reliant on the weather and swell!

Gina Spagarino 3G

Thank you! Quite unfortunate timing haha

Gina Spagarino 3G

So, looking at your final equation for that question, there should be no water in the reactants and only one water molecule in the products, but the 2OH- is correct!! sorry I made that more confusing with the incorrect first comment^^

Gina Spagarino 3G

Very Sorry, I read my work wrong. You should be adding 2OH- molecules to each side so that the the 2H+ and the 2OH- form 2 water molecules. Then those 2 reactant water molecules cancel with the 2 of the 3 water molecules in the overall reaction, leaving only one H₂O in the products.

Gina Spagarino 3G

I am not sure if you need the help with the other parts, but for the reduction reaction of ClO - + 2e- --> Cl - , first I added a water molecule to the products to balance the oxygen, then i added to H + to the reactants to account for the hydrogens in the water molecule. Then, since it is a basic s...

Gina Spagarino 3G

Hi, so for the oxidation 1/2 reaction (since Pb goes from 2+ to 4+ oxidation number electrons must be lost), the H in the reactant [Pb(OH) 4 ] 2- needs to go to something, so first i added 2H 2 ) to the products. This leads to a half reaction that is balanced in products and charge if you note that ...

Gina Spagarino 3G

You want to use the idea that E* is 0.0V since this is a concentration cell and the equation E=E*-(0.0592/n)log(Q), with n being moles of electrons transferred in the reduction of H + ... for some reason it works when you use the partial pressure and the hydrogen ion concentration together to find Q...

Gina Spagarino 3G

Hi! On your bottom one, the 2H⁺ and OH^- should combine to one H₂O for the reactants, not 2. So, that water cancels and there are no water molecules in the reactants, and one water is left in the products after the cancelling.

Gina Spagarino 3G

The reaction with the higher reduction potential must be at the cathode since E_cell=E*_CATHODE-E*_ANODE, and for it to be spontaneous E must be positive so the smaller number must be subtracted as the anode's reduction potential.

Gina Spagarino 3G

I was not aware that the 2 in front of the Fe 2 O 3 also applied to the hydrate at first and I was confused as to why I was getting the question wrong. Also, my method for balancing slightly differed from the above, I said 2Fe+ 3/2O 2 +3H 2 O --> Fe 2 O 3 *3H 2 O then just doubled the coefficients t...

Gina Spagarino 3G

I love burritos and also thai food, especially pad see ew, panang curry, and tom kha

Gina Spagarino 3G

entropy (S) is k_blnW, so then do S/k_b=lnW, then do e raised to the power of each side (since ln is then cancelled)... so e^S/kb=W

Gina Spagarino 3G

Another thing to note is that Reversible expansion more work than irreversible, which Dr. Lavelle mentioned in his lectures and is also applicable to a textbook problem

Gina Spagarino 3G

I noticed that of the questions on weeks 5/6 used the wording "as written" and "opposite as written" instead of "forward" and "reverse"

Gina Spagarino 3G

I'm in Anthro 3 culture and society right now and it is a great class!

Gina Spagarino 3G

Hi, I notice that I did the opposite for the V1 and V2 as above, but my answer registered in SAPLING. My question said the gas is compressed to 1/6 of its original volume, and I solved the equation using ln(1/6), and you can just plug in your given ratio for V2/V1. This makes sense because if V1 wer...

Gina Spagarino 3G

I use the idea that pressure and volume are inversely related to remember that this is for constant temp, and not pressure. Since there are 2 different volumes being plugged in, the volumes are changing, and therefore are not constant, so neither are the pressures (then it is constant temp because w...

Gina Spagarino 3G

2C2H6(g)+7O2(g)⟶4CO2(g)+6H2O(g) That is the equation used, maybe you are plugging in wrong values from the table? There H 2 O has a gas and liquid row, but it also may just be mistyping? Since your free energy valued for the table are not listed, I tried copy and pasting them from the table into the...

Gina Spagarino 3G

I find it helpful to remember to multiply the answer for the second part of your addition equation, with the entropy found using delta S=c v ln(T 2 /T 1 ), by physically crossing out the units as they cancel... since SAPLING wants the units in J/K, you know to multiply by moles, even though it is no...

Gina Spagarino 3G

I also thought of each step as a "Hess-like" problem. Since the second equation needs to be flipped and doubled, multiply delta H and delta S by (-2). Then, plus in the entropies/enthalpies for both reactions into the Gibbs Free energy equation. Then, once again using Hess's method, you ad...

Gina Spagarino 3G

I find the textbook problems very helpful, especially writing down specifically what I did wrong so I can reread it and know not to make that specific mistake again.

Gina Spagarino 3G

I really liked the show "Psych" when I was younger, I just rewatched it and understanding most of the jokes makes it much funnier now

Gina Spagarino 3G

Thank you! I also happen to do textbook problems last minute from procrastinating, this makes me feel much better about it :)

Gina Spagarino 3G

Because constant pressure calorimetry can change pressure to remain constant, it is not sealed. The bomb calorimeter is sealed and jas a steel container (which has the sample) submerged in water.

Gina Spagarino 3G

Heat capacities are always positive. It is the heat required to raise temp of an object by 1 degree celcius and is measured in a calorimeter... A negative amount of heat would not raise the temperature.

Gina Spagarino 3G

I have found Peach Pit [the band, they also have a song titled "Peach Pit"] to be very pleasant to study chem to [the pleasant counters the unpleasant... neutralization if you will]

Gina Spagarino 3G

Saying a negative amount of heat is released would make it seem like that heat is being absorbed and not released, but I do not think Lavelle would try to trick us with that combination

Gina Spagarino 3G

After doing all the problems, I like to go through and redo the steps on my calculator to make sure I didn't enter something wrong. It does not take too much time either since everything is written out already. On the midterm, this saved me for one problem because I had mistyped the first time going...

Gina Spagarino 3G

Aqueous is included in K as everyone said above... perhaps you were thinking of counting moles per side with Le Chatlier's, because that is just gas and aqueous is not included

Gina Spagarino 3G

A lovely message, thank you :) I slept in a lot later than I normally did Saturday morning, then watched some shows as well.

Gina Spagarino 3G

The smaller the pKa, the stronger the acid, because of the -log step (ex. a Ka of x 10^-2 becomes a pKa of 2, which is stronger than an acid with a Ka of x 10^-4 that becomes a pKa of 4)

Gina Spagarino 3G

Salts are ... acidic if they contain the anion of a strong acid (Cl-), but the cation of a weak base. ... basic if they contain the cation of a strong base (so cations from first two groups), but anion of a weak acid. ... neutral if they contain the cation from a strong base (K+) and anion from a st...

Gina Spagarino 3G

Because you are given the concentration of solution in Nh 4 Cl, which you are told acts as a weak acid, you are going to want to use the Ka to find the concentration of H3O+... so use kw to convert the given kb to ka, then do the ICE table, etc. like the previous SAPLING problems (rather than try to...

Gina Spagarino 3G

The sign changes bc one direction is endothermic and the other is exothermic... so magnitude stays the same but the sign switches.

Gina Spagarino 3G

Going from liquid to a gas requires heat, so we heat the liquid; but, added heat is going to the breaking of bonds (bc of IMF so that the phase may change from liquid to gas) and the temperature of the sample remains constant.

Gina Spagarino 3G

If you put K in front of Q in the comparison [K>Q or K<Q] the comparison sign points to the direction the reaction shifts, I double check that my logic behind which direction to shift is correct with this [ex with K>Q there must be more products at equilibrium there must be a higher concentration of...

Gina Spagarino 3G

Instead of using the reverse reaction's Kp, I just said the equilibrium concentrations of the reactants were equal to x;it still works out mathematically to get the correct answer because the reverse's Kp is the inverse, and the concentrations would be set up inversely as well... so keeping it with ...

Gina Spagarino 3G

On the SAPLING with the questions about temp changes and k changes, I found it helpful to think about which direction the reaction will shift based on whether the forward or reverse was endothermic, then whether K would have to increase or decrease to cause a shift in this direction when compared to...

Gina Spagarino 3G

I also had written small to be 10^-3 in this course in particular in my lecture notes and for the AVFT lectures

Gina Spagarino 3G

Writing when to do everything in my planner has helped me actually do assignments closer to when I planned to, rather than putting it all of until right before it is due. For me personally, I am more productive when I make sure I do one activity (surf, walk, run, yoga) per day because it serves the ...

Gina Spagarino 3G

Last quarter I got credit for responses that were similar to other ones, and I personally find it helpful to read the explanations phrased in different ways on other people's posts.

Gina Spagarino 3G

simplifying the n/v in the equations, P=(conc)RT which shows clearly where to plug in a given molarity

Gina Spagarino 3G

From the examples we did in the audiovisual focus topics, the unit it mol/L because we used molarities.

Gina Spagarino 3G

The concentration of a liquid that is a solvent may change, but not enough that the change is substantial (such as adding or subtracting a one from a million, the change is insignificant), and the molar concentration of a solid (mol/L) does not change because it is not dissolved in solvent so the co...

Gina Spagarino 3G

If you write it with K first, the arrow points in the direction that the reaction will proceed to reach the equilibrium concentrations... So when K<Q there is more products at that time then at equilibrium so the reaction proceeds to the left (backwards) creating more reactants... when K>Q there is ...

Gina Spagarino 3G

In theory I would like to reread my study guide in the middle of break and then right before 14B starts which is not that ambitious on its own, but realistically I will be only be rereading it once right before it starts

Gina Spagarino 3G

Dr. Lavelle, Thank you for taking the time to prepare the many hours of resources throughout this quarter, and I am glad you are the instructor for 14B next quarter. I really appreciate you adding the 10 points and considering all the added difficulties due to the online format. I hope you have a lo...

Gina Spagarino 3G

I thought it was a lot harder than the 2 midterms and I had a lot of time left on both midterms and none on this, but the 10 points is much appreciated

Gina Spagarino 3G

We have until Thursday at 10am to finish our posts here for credit!

Gina Spagarino 3G

I am going to try to do more practice problems regularly rather than just before the exams since this quarter I tended to cram them in all at once the week before the tests

Gina Spagarino 3G

I wanted to leave a note that a molecule that has polar bonds of the same element may not always cancel out to make the molecule non-polar because it also depends on the shape (ex. an angular molecule whether it be sp^{2 or 3} is nonpolar even with 2 of the same element attached to the central atom.)

Gina Spagarino 3G

Just remember that the angles are not the same... the angle of the angular for the sp² hybridization is less than 120 degrees while that of sp³ is less than 109.5

Gina Spagarino 3G

When all the electron densities are occupied by bonded atoms for a hybridization -- sp, sp², sp³, sp³d, sp³d² -- then the shape is nonpolar. THe other additional two are linear for the sp³d or sp³d² hybridizations

Gina Spagarino 3G

This quarter feels like it went by quickly & I'm nervous about the final, but I am ready for break (but also a little nervous about that bc I need to take the NREMT test)

Gina Spagarino 3G

I liked the example that the electrons "go back" to where they "came from," or thinking of the compound as if it were made of ions and not bonded covalently... so in a coordinate covalent bond, both electrons "go back" to the ligand for each bond

Gina Spagarino 3G

If a symmetrical molecule has all polar bonds, but of the same element, it is a nonpolar molecule . So, the B--F bond in BF 3 is polar because of F's higher electronegativity, but the molecule itself is nonpolar. If the charges cancel (which only happens with symmetrical shapes), the molecule is non...

Gina Spagarino 3G

Since there can be different shapes for a particular element within a compound, it would make sense for it to be labeled or have an arrow of some sort to specify on a test if they are different (ex with H 2 CCCH 2 there are 2 carbons that are trigonal planar but the middle carbon drawn in the Lewis ...

Gina Spagarino 3G

I find it helpful to think about the hybridization shape with all the electron densities being bonded atoms... so for this, there are 6 densities so a sp 3 d hybridization... the overall shape of these densities is octahedral, and it would be octahedral still if there were 6 atoms. But because there...

Gina Spagarino 3G

The seesaw shape for sp³d will always be polar bc of the asymmetry caused by the lone pair... only the trigonal bipyramidal shape or linear shape for atoms with the sp³d can be nonpolar if the attached atoms are all the same

Gina Spagarino 3G

T shape will always mean polar... of the different trigonal bipyramidal orbital arrangements with the sp³d hybridization, only the trigonal bipyramidal with 5 attached atoms or the linear model with 2 bonded atoms and 3 lone pairs can be nonpolar given that their bonded atoms are the same.

Gina Spagarino 3G

The element or compound with stronger intermolecular forces (so more polarizable) has a higher melting point because then it takes more energy to overcome those IMF.

Gina Spagarino 3G

I just reread the syllabus and I thought the fact that..." Should unexpected events (as announced by UCLA) result in a specific test or exam not occurring then final grades will be assigned based on completed work" is interesting, and usually would not appear relevant, but the way this yea...

Gina Spagarino 3G

My friend just showed me a study about the positive effects cold water can have on your body, so if you are by the ocean, going for a dip can be a nice (but quite chilly) way to give a shock to your body but in the good way :)

Gina Spagarino 3G

I believe the professor said we won't be given just names though, since he said not to worry about memorizing chemical formulas for compounds.

Gina Spagarino 3G

Drawing out the Lewis structures shows the way to add to atoms to a central atom with no lone pairs would be with a 180 degree angle to have the bonding pairs as far away as possible. I found it helpful organizing the different combinations of atoms/lone pairs into a chart for reference.

Gina Spagarino 3G

Hi! My #18 on Sapling also asks to arrange 3 molecules by the strength of their LDFs, but just has diatomic molecules... none like CH3C(CH3)2CH3. I know some Saplings are in different orders, but I never had a question like that, so I am just confused.

Gina Spagarino 3G

I was also confused by this since the oxygen was bonded to a carbon, but another way to think about it is that both compounds involved in the hydrogen bond have either an N/O/F, but one is bonded to a Hydrogen and the other just needs to have an electron pair to actually form the hydrogen bond. In t...

Gina Spagarino 3G

No, the hydrogen bond is between the N/O/F that the hydrogen must be bonded to and another N/O/F that has a pair of electrons to form the bond. The H will always have a slight positive charge in this case, so the hydrogen bonds will always include a H and a nitrogen, oxygen, or fluorine atom.

Gina Spagarino 3G

Polar molecules, so an atom has a higher electronegativity than other atom(s) [like you said] in the compound, will have dipole-dipole interactions. So, as long as the both compounds do not evenly share electrons [nonpolar], there will be possible dipole-dipole moments as an intermolecular force. Si...

Gina Spagarino 3G

@ the H bonding-- Hydrogen bonds form when a Hydrogen is covalently bonded to an N, O, or F, and is close to another N, O, or F that has an available lone pair (to actually form the H bond). It is easy to remember these 3 elements because they are the top right of the periodic table (excluding the n...

Gina Spagarino 3G

I believe what you said is exactly right. A larger atomic radius translates to a weaker covalent bond since the bond is longer, but for LDF the larger atomic radius means a more polarizable electron cloud, so stronger intermolecular forces.

Gina Spagarino 3G

I think about the other trends as they relate back to the atomic radius trend of increasing down a group and decreasing across a period. Because electrons further away from the nucleus are easier to remove, the ionization energy trend is the opposite of atomic radius (the smaller atomic radii at the...

Gina Spagarino 3G

Lewis bases are electron rich and donates the electron pair, and lewis acids are electron deficient and accepts the electron pair :)

Gina Spagarino 3G

I believe one type of problem where we would find the formal charge of each atom (where it may not explicitly ask) would be finding which Lewis dot structure is the best/most stable representation..

Gina Spagarino 3G

Because the d orbitals in the valence shells can accommodate additional electrons, the expanded octets have an electron configuration of s² p⁶ d², rather than the octet guideline of s² p⁶

Gina Spagarino 3G

Hund's Rule is that electron repulsions causes electrons in the same subshell [s,p,d,f] to occupy different orbitals with parallel spin. The Pauli exclusion principle says that there are no more than 2 electrons per orbital, and if there are 2 electrons in the same orbital (same first 3 quantum numb...

Gina Spagarino 3G

Thinking about the 2 diagrams from the lecture helped me with this problem. If the wave appears normal but the lines both end high or both end low, then it would not be normal once connected into a circle.

Gina Spagarino 3G

ms gives further specification to an electron with a specific ml. So, 2 electrons can have the same n,l, and ml [so same first 3 quantum numbers], but only one electron can have an ms of +1/2, and one electron can have an ms of -1/2. With ms as the fourth quantum number, no electrons have the same 4...

Gina Spagarino 3G

From my understanding, vertically is prioritized because of the additional shells in the cases of atomic radius and ionization energy, but electron affinity has more to do with filling the shells than periodicity.

Gina Spagarino 3G

To calculate the energy of the electron, use DeBroglie's: lambda=h/p (with lamda as the bacterial length)... and then use ((the p you solved for)/(electron mass)) as the velocity [p=mv so v=p/m]

Gina Spagarino 3G

for the last part of your question..."shell" refers to the principle quantum number, n, and "subshell" refers to the angular momentum, or the subshell/orbitals or s/p/d/f. So, the fourth shell would be when n=4, and the orbital/subshell can be l=0,1,2,3 for the "4th shell&qu...

Gina Spagarino 3G

From another example, delta x was found using a given uncertainty in momentum (ex "speed is known within +/- 1.00 mm/s), without giving a specific +- for the delta x because the delta x value can be solved using the equation (delta p)(delta x) is greater than or equal to h/4pi... in the example...

Gina Spagarino 3G

Just from the example he gave with 2 sets of a light source/detector, Dr. Lavelle said we would not know the pathway the electron takes after entanglement [as everyone mentioned above], but we would know the time because both the first and second detectors would still pick that up.

Gina Spagarino 3G

Amplitude determines the intensity or brightness of radiation, and increasing the intensity of light increases the number of photons. This does not affect the frequency or wavelength of these photons, so if they did not have enough energy to overcome an electron's threshold energy, increasing the am...

Gina Spagarino 3G

Since quarantine started, I have found that going on walks and listening to music can be a nice way to clear your mind and still got some sort of exercise in without the physical strain. I also feel more relaxed after laying at the beach or a dip in the ocean.

Gina Spagarino 3G

The equation is just saying the kinetic energy of an electron is the photon's total energy - the energy required to remove an electron. Just remembering this concept gives the equation, and the equation sheet does remind you that this is also equal to 1/2mv^2.

Gina Spagarino 3G

low frequency light, even with a high intensity (more photons), cannot eject electrons because it does not overcome the energy threshold which is a way in which light does not act like a classic wave. With high frequency light, even low intensity light can eject electrons.

Gina Spagarino 3G

Just to add to the noted difference that intensity deals with the number of photons and energy is frequency and wavelength-- if radiation is not strong enough to overcome the threshold energy, just increasing the intensity will not lead to the ejection of an electron since this is only increasing th...

Gina Spagarino 3G

I also thought taking notes on an iPad would be a better option and after talking to some friends and seeing their notes, I decided to order one with the pencil. This was before our classes started-- I just wanted to caution you that the iPad (normal, not air or pro) that comes up on the Apple websi...

Search found 108 matches