CHEMISTRY COMMUNITY

Charmaine Ng 2D

A negative delta G means a reaction is spontaneous!

Charmaine Ng 2D

Since bond enthalpy is the energy needed to break a bond, it is always positive since energy is required to break bonds.

Charmaine Ng 2D

You add Pt for sides that have no conducting metals! :))

Charmaine Ng 2D

You use q=mCΔT for closed systems!

Charmaine Ng 2D

Yes, you still need to raise the coefficients as the power! :))

Charmaine Ng 2D

Q has the same setup as K, but measures when the solution is not at equilibrium. Therefore, Q=K at equilibrium.

Charmaine Ng 2D

To find n, you balance the two half reactions to see how many electrons were transferred! :))

Charmaine Ng 2D

I'm hoping they'll be given, but I think we should prepare for in case they won't be

Charmaine Ng 2D

It will be zero in a concentration cell! :))

Charmaine Ng 2D

E naught is E under standard conditions! :))

Charmaine Ng 2D

You balance your half reactions to see how many electrons are transferred in the whole reaction! :))

Charmaine Ng 2D

Since Q is found by the concentration of products over concentration of reactants, Q = [Mg2+]/[Fe2+]

Charmaine Ng 2D

I just remember the two words that begin with vowels (anode and oxidation) are together while the two (cathode and reduction) are together! Since anode is where oxidation occurs, it's losing an electron, while reduction occurs at the cathode where the reaction gains an electron. Therefore, the elect...

Charmaine Ng 2D

You can balance this equation without the electrons, so you don't need those, and you also don't need the parentheses! :))

Charmaine Ng 2D

Hey, this question was confusing at first because there aren't obvious half reactions, but what you do is you write the half reactions for chlorine becoming an anion and lithium becoming a cation. So Cl2+2e - --->2Cl - . Hope this helps! I did the same thing!! identify which ones are reduction/oxid...

Charmaine Ng 2D

You have the anode where the cathode is and vice versa! Just switch them :))

Charmaine Ng 2D

Taha 2D wrote:it depends on the units you used to solve the question. the two options are R= 8.314 J/mol.K or R= 008206 L.atm/mol.K

I agree! Generally, we usually use 8.314, while 0.08206 is used for PV=nRT. That's just generally though, so it's always safer to check by units

Charmaine Ng 2D

Delta G determines whether a reaction is spontaneous or not, and as other replies have said, you would figure that out based on the equation, DeltaG = DeltaH - (Temperature x DeltaS)

Charmaine Ng 2D

Thanks for sharing this! It's such a cute way to remember it haha

Charmaine Ng 2D

If the change in Gibbs Free Energy is positive, it's unstable!

Charmaine Ng 2D

Like everyone else said, I think a week or a little more!

Charmaine Ng 2D

According to Sapling, "A greater increase in disorder, which correlates to a larger molar entropy of vaporization, indicates a more ordered arrangement of the molecules in the liquid state. Therefore, the most ordered liquid is the one with the largest ΔSvap and the least ordered liquid is the ...

Charmaine Ng 2D

I get confused over this too ahh but I think usually 0.08206 is used for PV=nRT and 8.314 for other cases. This is super general though, so it's safer to go by units and seeing what will cancel out! :))

Charmaine Ng 2D

I usually add 273.15 just to be safe! :))

Charmaine Ng 2D

Dr. Lavelle taught that it's a measure of possible microstates of a system, but if it's easier to think of it this way, it's also the measure of randomness or disorder in a system! :))

Charmaine Ng 2D

You use 8.314 for this case, but in other problems, make sure to take a look to see which units would cancel out!

Charmaine Ng 2D

I agree with the other responses! ^^ Q is negative when heat is released, while it's positive when heat is absorbed. Similarly, work is positive when work is being done on the system, while it's negative when the system is doing work.

Charmaine Ng 2D

The side that is hotter will be losing heat, while the colder side will gain heat. Therefore, the side that loses heat will be negative, and the side that gains heat will be positive.

Charmaine Ng 2D

Yep, you would still take them into consideration for the exponents! :))

Charmaine Ng 2D

I think part of it is definitely some trial and error, but it also helps to find the specific compounds in the given chemical equation, and to flip the equations according to the compounds you're looking for. Because you must end up with certain compounds, you also know that those specific ones must...

Charmaine Ng 2D

Q would be zero, since no change in temperature also means no heat is transferred

Charmaine Ng 2D

Hello! I've been consistent and on top of my chemistry community posts every week, but my CCLE grade says that I only have 22/25 points, and was wondering if there was a way I could fix this? I'm not sure if maybe I'm just missing it, but I can't seem to find Dr. Lavelle's email, so if anyone has th...

Charmaine Ng 2D

You use Kelvin so that the units cancel out! :))

Charmaine Ng 2D

Yep, endothermic will always be positive, since an endothermic reaction always takes in energy, while exothermic will always be releasing, and therefore always negative :))

Charmaine Ng 2D

Temperature is the only factor that can affect the equilibrium constant! :))

Charmaine Ng 2D

I think I remember a TA mentioning that it was a strong acid! :))

Charmaine Ng 2D

Can someone clarify to me the difference between K and Kc? I'm not sure exactly when to use which one. Thank you!! :))

Charmaine Ng 2D

To switch between Ka and Kb, you can use: Ka x Kb = 1.0x10^-14 (this is Kw!)
So,
Ka = 1.0x10^-14 / Kb
Kb = 1.0x10^-14 / Ka

hope this will help with the rest of your calculations! :))

Charmaine Ng 2D

I'm not completely sure, so it'd be great if someone could fact check me!: We've mostly been working with monoprotic acids, so this holds true for most of the problems we've done. However, note that it depends on the chemical equation's coefficients. If, for example, two moles of A- are gained from ...

Charmaine Ng 2D

Since heat is lost, Q would be negative!

Charmaine Ng 2D

You use ICE box whenever you're given an initial concentration and need to know the concentrations at equilibrium. You can also use it backwards if given a pH, and want to find the initial concentrations! :))

Charmaine Ng 2D

Ka is a measurement of dissociation, and pKa is the negative log of Ka. pKa is for simplicity's sake, just because it's easier to discuss chem saying, for example, a pKa=14.98 rather than a Ka=1.044x10^-15. Because pKa is the negative log of Ka, a higher pKa means a smaller Ka (weaker acid), while a...

Charmaine Ng 2D

Since you're given the initial concentration for the acid, set up an ICE table, where the equation for the monoprotic weak acid would be HA(aq) + H2O(l) <---> A- + H3O+. On the left side, water won't count since it's a liquid, but HA would be losing x moles/Liter, so it would be -x. Meanwhile, A- an...

Charmaine Ng 2D

Set up an ICE box table to find the equilibrium pressures, solving it like a normal ICE box problem, and then add all the equilibrium pressures for the total pressure.

Charmaine Ng 2D

Yes, the Q value is the ratio of product/reactant concentrations not at equilibrium, and yes, it should eventually reach equilibrium!

Charmaine Ng 2D

Since 1mol was added to the 1L, (which is 1 Molarity), you add the 1.00 to the 1.94 Molarity of NO2, which means you have a starting concentration of 2.94 NO2 and 0.335 Molarity of N2O4. Since NO2 was added, it'll shift left towards the reactants. Set up an ice box with these initial concentrations,...

Charmaine Ng 2D

Find the pressures at equilibrium and add them all to find total pressure :))

Charmaine Ng 2D

Since Q is similar to K, [product]/[reactants], except not at equilibrium, you can just take the numbers given and use them in [product]/[reactants] to find Q

Charmaine Ng 2D

Molarity is actually a measurement of concentration, which is mol x L^-1, so you already have the molarity of both! :))

Charmaine Ng 2D

We find Q when we don't know whether the reaction is at equilibrium or not, and we use K when we are certain that the reaction is at equilibrium. Q is just a measure of the ratio when we don't know!

Charmaine Ng 2D

I think the course will focus on using atm and bars for the most part! :))

Charmaine Ng 2D

I agree with the other replies! I think that you need to take the whole system into consideration when considering whether it's homogeneous or heterogeneous.

Charmaine Ng 2D

The concentrations might change, but the mixture would eventually reach equilibrium at K again, so I don't think it will affect K!

Charmaine Ng 2D

Concentration is a measurement of moles/Liter, and since you can't measure negative moles or negative Liters of something, it's not possible for concentration to be negative!

Charmaine Ng 2D

Since water is amphoteric, it has properties of both an acid and a base!

Charmaine Ng 2D

Ka is a way of measuring the dissociation of a weak acid, so larger Ka numbers would mean more dissociation. pKa is just taking the negative log of the Ka value, so a lower pKa would be a "stronger" weak acid.

Charmaine Ng 2D

I agree with Andrew! ^^ I think Dr. Lavelle mentioned in lecture that it's when the coordination sphere is negative

Charmaine Ng 2D

It could be useful to know the actual wavelength numbers, but from what Dr. Lavelle has taught and tested us on so far, it seems like he just wants to to distinguish them based on their energy levels! So I wouldn't worry too much about memorizing the actual numbers

Charmaine Ng 2D

Ka measures the dissociation of a weak acid by calculating the concentration of its products over its reactants, while pKa is just the negative log of that for simplicity's sake!

Charmaine Ng 2D

Since Chlorine is more electronegative, it has more electron-withdrawing power, which makes the overall anion more stable.

Charmaine Ng 2D

The coordination number is a count of how many ligands are attached to the TM. Since atoms outside the brackets are not directly attached to the TM and therefore not ligands, they don't count for coordination numbers! :))

Charmaine Ng 2D

As others have said already, the oxidation of the Cobalt should be +3, not +2. The entire compound has a neutral charge, and taking the chlorine outside the brackets into consideration, the coordination complex should have an overall +1 charge. This means, within the brackets, Cobalt's charge + (-2)...

Charmaine Ng 2D

Coordination number is the number of ligands that are attached to the central metal atom, while oxidation state would be the charge of the central metal atom without its ligands and electron pairs This! ^^ Also, to figure out the coordination number, you usually check whether it's monodentate/biden...

Charmaine Ng 2D

I remember one of the UAs said that we should familiarize ourselves with everything on the Coordination Compounds worksheet, the one posted above ^^

Charmaine Ng 2D

^^ You alphabetize the ligands based on the ligand itself rather than the prefix! Add the prefix after :DD

Charmaine Ng 2D

Since Dr. Lavelle teaches both courses, I'd assume that they follow a similar format and structure! The lectures will probably be similarly posted, and homework will probably still be through Sapling! I wouldn't expect any major changes :))

Charmaine Ng 2D

Everyone's already said the key points, but I also wanted to mention that the difference between a 90% and an 85% is like one question. I know my numbers are off, but please remember to be kind to yourself if you are beating yourself over one question. I'd also like to mention that a lot of exam qu...

Charmaine Ng 2D

While double and triple bonds may effect polarity, electronegativity is the main factor that affects polarity. Since Arsenic is surrounded by 4 oxygens, and the oxygens are more electronegative than As, there will be diploe vectors pointing towards those 4 oxygens. However, all of them cancel out m...

Charmaine Ng 2D

I don't think it's ever too early to study for finals, and it's honestly great if you have time for it now so that you don't have to cram later! I've found Sapling problems and attending UA/TA worksheets the most useful, and would highly recommending using those sources as a way to refresh the conte...

Charmaine Ng 2D

Just as the replies above said, I would be hesitant on posting exam questions on chemistry community, but I think you can review your midterm during TA sessions!

Charmaine Ng 2D

35 posts overall, but also make sure that you have 5 per week! I think they count to make sure how many you have per week as opposed to the total number.

Charmaine Ng 2D

Yes, that's correct! All three have the same trends (increase across period and decrease down group) because they're all inter-related and follow the same reasoning! If you understand one, you should be able to figure out the others, like how the replies above have explained! All three have to do wi...

Charmaine Ng 2D

I like waking up a little earlier than usual just to take a walk around the block!! The chilly air is actually pretty refreshing! :))

Charmaine Ng 2D

Ahh I'm familiar with that feeling, but it's important to remember that your midterm grade doesn't determine your overall grade, nor does this one grade you get for the class determine your future! You have many more opportunities and chances to do better, so don't feel down!!

Charmaine Ng 2D

For me, I find it helpful just to know the general prefixes of the words, so to know that tri=3, tetra=4, etc. I've also found it helpful to practice arranging my Lewis structure diagrams in the shape of the VSEPR shapes when I draw them for homework and assignments so that they look like, for examp...

Charmaine Ng 2D

While having two N=O bonds would make it more "stable" due to the lower formal charges, Nitrogen is only in period 2 of the periodic table, which means it cannot hold more than an octet. A structure with 2 N=O bonds and 1 N-O bond would mean that N is sharing 10 electrons, exceeding the oc...

Charmaine Ng 2D

^^ My high school teacher also gave us a similar way to remember this! For polyatomic ions, the ones that end with "-ate" have one more than the "-ite," since it just "ate" hehe get it? AHAHA idk if this helps at all, but dumb ways to remember terms help me, so I hope t...

Charmaine Ng 2D

I'm in the same boat! I relate to always worrying about grades, but for this class, I wouldn't worry too much! Since you get full credit for Sapling and Chem Community as long as you stay on top of your assignments, just focus on understanding the material and performing well on midterms! You got it!!

Charmaine Ng 2D

I also agree! I'm really grateful for the Bruincast videos, and it definitely helps that I'm able to watch the lectures at my own pace, go back to rewatch, and pause to take notes, especially since I'm a slow note-taker. It's fun to be "in class," and it's definitely different from my othe...

Charmaine Ng 2D

Some people take them together, but I think most upperclassmen I've met have taken them sequentially, and I think that's recommended, but it's also up to you and how confident you feel about the 14b material! :))

Charmaine Ng 2D

If you take 14b with Dr. Lavelle again, then I think he styles his lectures the same way! I think they should be pre-recorded!

Charmaine Ng 2D

You can click the "Quick Links" in the upper left corner, and then click "Your Posts." That should lead you to both your posts and replies! :))

Charmaine Ng 2D

I personally like the workshops more than just doing a bunch of textbook problems nonstop, just because having a UA go through the problems with you to make sure you're doing it right helps a lot for me :)) I think they also try to pick the more difficult problems, so that definitely helps a lot! It...

Charmaine Ng 2D

Formal charges are for calculating which Lewis structure is the most stable for the molecule! The lower the formal charge, the more stable the structure is, which means the more likely the molecule exists with that structure.

Charmaine Ng 2D

Since double bonds are stronger, the bonds pull the electrons in tighter and result in a shorter bond length!

Charmaine Ng 2D

Other people have said this already, but it'll probably either be covered soon, or since it's not on the outline, won't be a big deal for this chapter!

Charmaine Ng 2D

At energy level n=2, the configuration would be 2s^2 2p^6, since two electrons fit in the s subshell and 6 fit in the p subshell, so 2+6 = 8 electrons! :))

Charmaine Ng 2D

For fluorine: oxygen has a lower first ionization energy because fluorine has a higher effective nuclear charge due to its extra proton, which means it'll hold onto its electrons tighter. It'll therefore take more energy to remove an electron from fluorine than from oxygen. For nitrogen: While the n...

Charmaine Ng 2D

For atomic radius, for each proton that is added, the radius gets smaller since the positive charge increases and will pull the electrons in closer. However, the atomic radius increases whenever an electron that is added lies in a new energy level, since a new energy level would make the size of the...

Charmaine Ng 2D

In this class at least, c will always be the speed of light! :))

Charmaine Ng 2D

As most other people have said, I'm pretty sure any post where you're engaging in discussion, asking a question, or helping other people out will count towards your 5 posts a week! :))

Charmaine Ng 2D

When I calculate the Energy for certain questions, I sometimes have trouble trying to tell whether the result is J/mol or J/photon. Is there any way to tell? For example, in the Sapling week 2,3,4 homework question, "A liquid is exposed to infrared radiation with a wavelength of 6.18×10−4 cm. A...

Charmaine Ng 2D

Yep, I'm pretty sure I remember my TA mentioning that Heisenberg could be on the test, since it was covered before today! I don't know how many will be on the midterm, but it's always good to familiarize yourself with it!

Charmaine Ng 2D

Yep, I think you just apply sigfigs at the end, so that the answer doesn't become too different with all the rounding and can remain as accurate as possible!!

Charmaine Ng 2D

As the answers before mine have said, the photoelectric effect proves that light is not only a wave, but also exists as photons, like packets of energy. This was proven by the fact that it took not higher intensity light, but actually light with higher frequency, to remove an electron, which meant t...

Charmaine Ng 2D

You're right about the frequency! It's the cycles that pass through within a given time, and is also indicative of the energy, since E=hv. Energy and frequency are proportional, so the higher the frequency, the more energy. Meanwhile, intensity refers to the amount of photons in a light beam, not ho...

Charmaine Ng 2D

Ahhh thank you thank you!! This helps so much!! :))

Charmaine Ng 2D

Hello! I had a quick question about finding which part of the electromagnetic spectrum a wavelength is from. I know that Dr. Lavelle said that there are 3 main groups of lights: 1) UV (involving the n=1 state) 2) visible region (involving the n=2 state) 3) infared (involving higher energy levels lik...

Charmaine Ng 2D

Yep! It's the threshold energy, so basically the energy needed to remove an electron!

Charmaine Ng 2D

Hello! For me personally, I've found that outlining my study plans ahead of time, along with clearing my workspace and working in a comfortable environment has really helped me! While I usually don't have much time to go over content ahead of time, I usually try to complete my work as soon as lectur...

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