CHEMISTRY COMMUNITY

ALee_1J

E naught is a state function? That's why it's capitalized? The only things we've learned that aren't state functions are heat (q) and work (w)? I'm not sure what you mean exactly. Edit: I see what you mean. I did a little research and apparently E naught isn't a state function. Idk when you'd add an...

ALee_1J

I might be wrong, but don't you just take the specific heats and multiply them by the moles to cancel the per mole unit and by the temperature in kelvin to cancel the per kelvin unit to get delta H in terms of J and then use the Hess type approach (products-reactants) to find the overall delta H rea...

ALee_1J

You really gotta think of this while looking at a reaction profile (energy vs time as the reaction progresses). Ea is the energy barrier so the height of the bump to the energy of the reactants. delta H is the difference in energy between the reactants and products. If you flip the reaction profile/...

ALee_1J

I believe O₃ --> O₂ and then Br- --> BrO₃^- + 6e-? I didn't check so my numbers may be off but that's who you should be dividing it. The oxygens have an oxidation state of 0. The Br- gets oxidized into BrO₃.

ALee_1J

If you look at the anode reaction, Cd (s) + 2OH- (aq) --> Cd(OH) 2 (s) + 2e-, there is OH- in the solution with the anode, Cd(s). OH- isn't stable by itself (in solid form) so in order to make that solution, you'd need to have it attached to something. At the same time, you don't want the cation to ...

ALee_1J

Cell reactions are kind of like the overall reaction while the half-reaction kind of tells you what's happening and what's reducing/oxidizing. It's kind of similar to elementary steps/reactions vs overall reactions in kinetics. If you look at part a, the Ag in the AgBr is being oxidized and becomes ...

ALee_1J

If you look at the anode reaction, Cd (s) + 2OH- (aq) --> Cd(OH) 2 (s) + 2e-, there is OH- in the solution with the anode, Cd(s). OH- isn't stable by itself (in solid form) so in order to make that solution, you'd need to have it attached to something. At the same time, you don't want the cation to ...

ALee_1J

If you're referring to P₄ --> H₂PO₂^- + PH₃ as the half reaction, it's not? That's the skeletal and you're supposed to break it up into two half reactions:
P₄ --> H₂PO₂^- + e-
P₄ +3e- --> PH₃

And then balance it like a regular redox.

ALee_1J

Reminder that it's the start of Daylight Savings in CA on that day! Please don't be late!

ALee_1J

I personally found Chemistry Libre Texts very helpful!

https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Redox_Chemistry/Balancing_Redox_reactions

ALee_1J

If you're referring to E naught (like E with the degree symbol), it's basically the E of the cell under standard conditions (298.15 K and 1 atm). E of the cell (without the degree symbol) means the E of the cell not under standard conditions.

ALee_1J

I try to have a set time every day to myself (no homework or studying during this time) to destress or relax. Like I set aside at least two hours a day for myself that is strictly reserved for doing fun stuff and stuff that I wanna do. You can do selfcare during this time or watch a quick episode or...

ALee_1J

I believe when the reaction is not under standard conditions. Bc the -0.0592 is calculated by plugging in standard temp and stuff into the equation.

ALee_1J

That helped a lot! Thank you Zoe and Sophia!

ALee_1J

In the beginning, one of the first things you're supposed to do is balance out the elements on either side of the half reaction EXCLUDING oxygen and hydrogen right? And then you don't really mess with the coefficients afterwards (like after adding H2O, you don't go back and multiply the whole reacti...

ALee_1J

At the end of balancing (when you add the two half equations together), are you allowed to have leftover H+ on either side? Are you allowed to have leftover OH- on either side? Does this depend on if the reaction occurs in acidic or basic solution?

ALee_1J

So I looked up how to balance redox reactions and was curious about a few things: 1. Can you add H+ to any side as long as there is another H on the other side? Does that H have to also be an H+ or can it be in a compound? 2. Similarly, can you add e- to any side as long as the charges are balanced?

ALee_1J

Gold has always been a highly prized metal, and it has been widely used from the beginning of history as a store of value. It does not rust like iron and does not become tarnished like silver. It is so chemically inert that it will not react with even the strongest concentrated acids. But it can be...

ALee_1J

Thank you!!!

ALee_1J

4I.1 What is the total entropy change accompanying a process in which 40.0 kJ of energy is transferred as heat from a large reservoir at 800. K to one at 200. K? text.jpg The solutions manual uses q/t which makes sense but can someone explain why one of the calculations is negative and the other is...

ALee_1J

Hi, yes I got that part. I was asking how to find the change in enthalpy for constant volume.

ALee_1J

For Textbook Problem 4C3 Part B: 4C.3 Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820mol Kr(g) at 298 K and 1.00 atm (a) at constant pressure (b) at constant volume. Treat the gas as ideal. For constant pressure we know that q p = delta...

ALee_1J

Does anyone know what the constants for calculating heat of an ideal gas at both constant volume and at constant pressure are (Cv and Cp)?

ALee_1J

To add to everything that's been said, reversible work of expansion is theoretical (correct me if I'm wrong) because it is based off of the idea that all energy can be turned into heat which is not possible since some energy/heat will be lost to the surroundings.

ALee_1J

I think the only professor teaching it next quarter is Dr. Casey... she's alright. I'll let those who also have her elaborate.

ALee_1J

Hi, if you're in the groupme for the chem 14B class, there is a link in the bio with an equations list (i'm not going to post the link though bc the forum is viewable to the public). you could also use the equations worksheet on Dr. Lavelle's site.

ALee_1J

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q=−3.50kJ), resulting in a temperature rise of 7.32C. In a subsequent experiment, 100.0 mL of 0.200 M HBr(aq) and 100.0 mL of 0.200M KOH(aq) were mixed...

ALee_1J

Yes, just theory but we will still be expected to know it (see lecture from Friday).

ALee_1J

It's not a rule that single reactant decomposing into products is endo or exothermic. You need to look at the bonds being broken (in the reactants) and the bonds that are being formed (in the products) to see if it's exo or endothermic (which is why they gave you the table). When the enthalpy in pro...

ALee_1J

Q refers to heat while H refers to enthalpy. They (for the most part) are not interchangeable.

ALee_1J

https://groupme.com/join_group/62288203/dSSkobMS

ALee_1J

The question states A 0.201 mol sample of N 2 (g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 15.1 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding tota...

ALee_1J

An insulated thermos was an example given in lecture (i think). I would say stick to open/closed systems because Dr. Lavelle mentioned that nothing really happens in isolated systems since we are assuming no matter or energy is being exchanged. If nothing is being exchanged, we can't really do any c...

ALee_1J

When you reverse a reaction, K is flipped. Ie. K_reverse = 1/K_forward

ALee_1J

Increase in pressure/volume has no effect on K. The only thing that affects K is temperature. That is the reason why the reaction shifts to the right or left when there is a change in pressure. When there is increased volume/decreased pressure, the reaction wants to go back to equilibrium and thus i...

ALee_1J

So from the lecture: A reversible process happens when the pressure of a system is similar to the pressure of its surroundings. The example given is the piston and how the two pressures were 2 atm/bar and something very close to two atm/bar. In a sense, the system and surroundings were in equilibriu...

ALee_1J

We haven't learned this yet, but from what I remember in high school, enthalpy is a measure of heat while entropy is a measure of "chaos"/randomness/disorder. This probably didn't help you very much,,, but we should learn entropy soon.

ALee_1J

Hi, I was wondering what materials we are allowed to bring in for the midterm (ie. calculator, periodic table, and constants and equations sheet) and how the midterm will work. Will the process be similar to last quarter where we use respondus and have a separate web cam for zoom? Or will we be atte...

ALee_1J

Hi, the only thing that seems off here is your K_a. I believe you calculated it wrong (K_w = K_a x K_b).

ALee_1J

The only thing that seems odd to me right now is your K_a value. Did you perhaps miss something? Because K_w = K_a x K_b and I don't think that K_a is correct? Because you didn't need to use the quadratic equation.

ALee_1J

I'm not sure about the first part of the question but I can take a stab at the second part. Formal concentration is the same as initial concentration but different from concentration at equilibrium. The [B] calculated using the [OH-] and the K b expression is the concentration of B at equilibrium. S...

ALee_1J

To add to what was said above, this problem is an example of working backwards (which is interesting since we don't get to do those a lot). I think that to find the percent protonation, the equation was [BH+]/[B formal ] where [B formal ] is [BH+] + [B at equilibrium ]. The [B] calculated using the ...

ALee_1J

Dr. Lavelle should have sent out an email detailing what will be covered. I think he gives us the corresponding problems to which topics he's stopping on.

ALee_1J

So you would basically solve an ICE table for the initial values: [N2O4] = 0.429 and [NO2] = 3.19 and solve for x. Here you are trying to find the final concentration after equilibrium has been reestablished. When equilibrium is reestablished, you will have the same ratio of reactants to products bu...

ALee_1J

The reason why Na+ stays an ion in water is because it's stable as is without having to react with water. CH3CO2- would be a proton acceptor and generate OH- ions because it's a weak base and reacts with water. If it were a salt of/ a strong acid or base, it would stay dissociated. Since it is a wea...

ALee_1J

Using [N2]=[O2]=0.100 M and [NO]=0.600 M, calculate the Ka value. This value will allow you to calculate the values at equilibrium should the reaction be disturbed. Then solve an ICE table with the values [N2]=[O2]=0.100 M and [NO]=0.900 M for the initial concentration. Reminder: solving for x doesn...

ALee_1J

You could, since I think acid/base equilibrium is part of Chem 14A.

ALee_1J

I don't know if this helps but: Since you are give the pKa of the conjugate acid of codeine (pKa = 8.21), you can calculate the pKb through the equation pKw = pKa + pKb. The pKa of the conjugate acid also tells you that codeine is a pretty strong base (please correct me if I'm wrong), since the pKa>...

ALee_1J

Yea, for some reason I got the same equation as Garmani.

ALee_1J

You would have to calculate the K value from two equations: H₂ (g) + Cl₂ (g) <--> 2HCl (g) and 2BrCl (g)<--> Br₂ (g) + Cl₂ (g).

I didn't include exact values in case you wanted to try it out, but the answer is in the solutions manual.

ALee_1J

As the previous answer stated, I think it really depends on the units. If you look at the constants and equations (there a new one for Chem 14B located on the class website), the R constant has units so just make sure that they cancel when you plug everything in.

ALee_1J

It's definitely possible, but it depends on the question being asked. I think here it's just a theoretical question as to which would increase or decrease, but in the real world, there will be factors that limit/affect the reaction.

ALee_1J

The volume doesn't decrease, from what I know, because 1) you aren't really changing the container even if pressure does increase and 2) inert gases don't react with the reactants. So theoretically, it's like the inert gas isn't there or doesn't make a difference in the space that the reactants of a...

ALee_1J

You distinguish acidic, basic, or neutral salts based on if it carries a acid or base. For example, NH 4 ClO 4 carries an acid (NH 4 + ). When put into water, the salt will dissociate and the NH 4 + will donate a proton to H 2 0 to create H 3 0 + and NH 3 . Because of the H 3 0 + s, the concentrati...

ALee_1J

You distinguish acidic, basic, or neutral salts based on if it carries a acid or base. For example, NH 4 ClO 4 carries an acid (NH 4 + ). When put into water, the salt will dissociate and the NH 4 + will donate a proton to H 2 0 to create H 3 0 + and NH 3 . Because of the H 3 0 + s, the concentratio...

ALee_1J

Typically, I would draw one just to be safe, but theoretically speaking, you don't if you know it well? Sorry, if this doesn't help|||-_-

ALee_1J

Why is HClO 2 a stronger acid than HBrO 2 ? The solution manual said that it was because Cl had a stronger electronegativity, but didn't we say that the strength of an acid was inversely related to bond length? ie. HBr is a stronger acid than HCl because the bonds are longer and weaker. Why is the o...

ALee_1J

Do we need to know oxyacids for the exam?

ALee_1J

A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared? The answer was: The pH of the desi...

ALee_1J

Why is the preferred Lewis Structure for N₂H₄:

instead of a structure with a triple bond in between the two nitrogens?

ALee_1J

Would T-shape molecular geometry be the same thing as trigonal planar? I mean, it's in the same plane (?) but the bond angles are different?

ALee_1J

Is the word alkaline synonymous to basic? ie. when you say a solution is more alkaline, it's more basic?

ALee_1J

I believe pentagonal pyramidal is wrong (correct me if I'm wrong) because it's not the most efficient way. Ie, you want your electrons as far away from each other as possible. Putting five electrons together in one plane (pentagonal) doesn't minimize the electron-electron repulsion. Hexagonal planar...

ALee_1J

In general, bond angles are determined by electron-electron repulsions. Lone pair electrons exert a "larger" repulsion than bound electrons which is probably the reason (?) why you got an unexpected bond angle. I don't think that we will ever be asked to determine exact bond angles(correct...

ALee_1J

HF is weak(er) when compared to HI etc. bc of fluorine's high electronegativity and thus strong bond to hydrogen. The stronger the bond, the harder it is to break or dissociate when added to water. How strong an acid or base here is actually inversely related to the bond strength and consequently th...

ALee_1J

To add to the answers above, a ligand is basically any molecule/compound bound to a transition metal. A way to quickly scan for how many bonds a ligand can form would be to look out for electron rich species in a ligand. Someone above mentioned NH 2 CH 2 CH 2 NH 2 and two nitrogens leading to two bo...

ALee_1J

Yes. You would need the individual oxidation numbers to figure out the transition metal's oxidation number for naming. Easy way to find oxidation numbers: For the s block, it's helpful to look at the numbers above each group (ie. group 1 is +1 while group 2 is +2). Similarly, for the p-block, just l...

ALee_1J

Yes! Strong acids and bases will most likely show up on the test since Dr. Lavelle went over how to figure out if an acid/base is strong. To add to the previous answers: -the higher the electronegativity, the stronger the bond (the less strong of an acid/base it is) -the smaller the electronegativit...

ALee_1J

In the previous lecture and today's lecture, how were we able to figure out that nickel was Ni²⁺ and cobalt was Co²⁺?

ALee_1J

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 que...

ALee_1J

To add, typically hydrocarbons (molecules with only hydrogens and carbons) are linear/chains. So all you really need to do is draw the carbons, put in the hydrogens, and then fill in the double bonds of the carbons where necessary.

ALee_1J

To add to the answers above: Double bonds are indeed "shorter" than single bonds, but the structure you are looking at right now is a resonance structure so all of the bonds will be equal (ie. less than a single but more than a double bond). So I believe the angles will all be equal ( but ...

ALee_1J

I would suggest redoing the textbook problems that were assigned to us and reading the textbook. Something that I like to do is create flashcards to quiz myself on key concepts. If more people are interested, we could also form a study group to discuss difficult topics and work on problems together...

ALee_1J

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...

ALee_1J

Select the correct statement about the relative positions of the hydrogen atoms in the three structures: a) The hydrogen atoms of H 2 CCH 2 and H 2 CCCCH 2 lie in the same plane. b) The hydrogen atoms of H 2 CCH 2 and H 2 CCCH 2 lie in the same plane. c) The hydrogen atoms of H 2 CCCH 2 and H 2 CCC...

ALee_1J

To add to the post above, the smaller the atom/molecule is, the less polarizable it is which describes the character of the bond.

ALee_1J

Hey David, Yea it's kind of weird because for the textbook problems, it seemed like formal charge wasn't what determined which atom has the unpaired electron. However, from what I've seen it seems like the most electronegative atom will want the full octet, so the less electronegative species will ...

ALee_1J

for fluorine:
Fc double bond= 7-((4/2) + 4)= -1
Fc single bond= 7-((2/2) + 6)=0

for nitrogen:
Fc triple/three bonds = 5 - ((6/2) + 2) = 0
Fc four bonds = 5 - (8/2) = +1

ALee_1J

In general, expanded octet is when the central atom has more than 8 valence electrons/can make more than 4 bonds. The reason certain elements can do this is because of the d orbital. The element accepts extra electrons and puts them in the d orbital therefore only elements with n>2 can have an expan...

ALee_1J

He is considered an inert gas because it has 2 electrons in the s orbital. Therefore adding electrons to its shell is not favorable while fluorine desperately wants to fill the p-orbital/is about to complete its octet.

ALee_1J

Which M⁺ ions are predicted to have the following ground state e^- configurations?
a) [Ar] 3d⁷
b) [Ar] 3d⁶

Could someone explain this? I didn't really understand why a) was Co²⁺ and b) was Fe²⁺. I thought a) was copper and b) was nickel.

ALee_1J

Determine the number of electron pairs (both bonding and lone pair) on the iodine atom in: ICl 2 + , ICl 4 - , ICl 3 , and ICl 5 How do you figure out how many electron pairs iodine has? I noticed that sometimes iodine has more than four bonds but also has lone pairs and other times it has only two...

ALee_1J

Found this post in a previous year: A formal charge has a value of either a positive integer, a negative integer, or zero. A partial charge usually has a positive or negative non-integer. Each atom in a molecule has both, but in this course, we're only able to calculate the formal charge. For the pa...

ALee_1J

Polarizability is a measure of how easily an electron cloud is distorted by an electric field. I.e. can I pull all the electrons to one side of the atom to create a slightly positive side and a slightly negative side. Basically, the more tightly held the electrons are, the less polarizable they are....

ALee_1J

Hydrogen bonding acts more like a dipole-dipole bond or electrostatic attraction. Hydrogen bonding isn't actual bonding in the way that covalent bonds are bonds. Hydrogen bonding is just attraction/intermolecular force.

ALee_1J

Hi, I believe that this refers to the electron density. Like, the atomic orbitals are drawn as spheres or balloon looking structures (the very first lecture on orbitals) to show that there is a higher chance the electron could be found in this area. But I could also be wrong |||-_-

ALee_1J

It's been on my mind for a while but... when you microwave food, are you just exciting the electrons in the food and is the heat the energy that the electrons give off when they return to ground state?

ALee_1J

In ion-ion interactions (say, Na+ and Cl-), the energy of the interaction is -250kJ/mol. Dr. Lavelle said that it's 250kJ per mole of INTERACTIONS. Does this mean that for one mole of Na+ and one mole of Cl-, the energy of their interactions is 250kJ?

ALee_1J

Are hydrogen bonds (from hydrogen bonding) an actual bond or is it just an attraction force/electrostatic attraction?

ALee_1J

Are Group 13 elements always electron deficient or does it depend? Also, does electron deficient (the way that Dr. Lavelle uses it) mean that the atom/element can be without an octet?

ALee_1J

Why does NO₃^- have nitrogen as the center atom? I know that center atoms are the ones with lowest ionization energy but doesn't oxygen have a lower ionization energy than nitrogen due to its lone pair and electron-electron repulsion?

ALee_1J

In Monday's lecture, why did Dr. Lavelle say that nitrogen had a lower ionization energy than oxygen? Didn't he say that oxygen had a lower ionization energy due to the one electron pair and electron electron repulsion?

ALee_1J

Lewis structures have limitations on how well they can represent molecules. Is resonance the name of a limitation or is it a way to overcome the limitation?

ALee_1J

I think there are more elements that are exceptions but Dr. Lavelle has only talked about the first four elements being exceptions to this rule.

ALee_1J

Electron affinity is how much energy is produced/absorbed when an atom accepts an electron. This is based on how much an atom "wants" an electron and electronegativity. For example, F is very electronegative and will release energy when it accepts an electron. Ne or Li on the other hand wo...

ALee_1J

I think you'd have to look at the periodic table too. Like n=1 only has the s-orbital, n=2 only has the s and p orbital, and then n=3 has s and p and d orbital, etc. If I remember correctly, l = (n-1), like the highest possible l.

ALee_1J

Because the US wanted to be special and declare their sovereignty... and then we never bothered to think how much easier it would be to just go to SI and just switch.

ALee_1J

Most relevant units and conversions will be provided on the constants and equations sheet that Dr. Lavelle provided us with.

ALee_1J

Ground state is when the electrons are all in the configuration you would expect them to be in (ie. carbon would be 1s 2 2s 2 2p 2 ). Like you could accurately find the electron configuration just by looking at its position. The excited configuration is a bit different since the electron configurati...

ALee_1J

Why is (NH₄)_sSO₄ a salt? I thought salts were a metal and a nonmetal? ie. NaCl is a salt because Na+ is a metal and Cl is a nonmetal.

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