CHEMISTRY COMMUNITY

Jessica Castellanos

For a detailed description and related exercises, check p.264 in the textbook and 4C exercises.

Jessica Castellanos

Which side of the concentration cell is the negative electrode? Thanks!

Jessica Castellanos

Thank you so much for all your help for the past two quarters :)

Jessica Castellanos

Based on just definitions, isochoric means constant volume while isometric is having equal dimensions. I hope this helps.

Jessica Castellanos

When given a reaction mechanism, the catalyst will be in the reactants side, will be used up, and then produced again by the end, so that in the overall reaction the catalyst isn't used up.

Jessica Castellanos

The easiest way I can explain this is by an example:
Let's say,
A + B → X
and X → C + D

Then, for the reaction A + B → C + D, X is the intermediate species because although it cancels out and isn't present in the overall reaction, it was still a species in the process.

Jessica Castellanos

What is the difference between a reaction mechanism and an elementary step?

Jessica Castellanos

What would be a situation in which to use the arrhenius equation? Is it just to plot ln K vs 1/T?

Jessica Castellanos

The amount of e- on both sides should be equal for the redox reaction to be fully balanced. You can try multiplying one or both the half reactions to get equal electrons on each side.

Jessica Castellanos

Can someone explain how electron transfer in concentration cells occurs?

Jessica Castellanos

The n represents the electrons transferred in the redox reaction. So to do that, find the oxidation states of the reactants and products, identify the reduction and oxidation reaction, balance the charges, and the total amount of electrons transferred in this reaction is the n value.

Jessica Castellanos

To figure out which is the oxidation and which is the reduction reaction,The first step is to figure out the oxidation states of each element in the reactants side and products side (there is a video on Khan Academy on common oxidation state patterns). Then, compare each element's oxidation state fr...

Jessica Castellanos

The unique rate would be -(1/b) × d[P]/dt= (1/a) × d[R]/dt

Jessica Castellanos

If there is a solid only on one side, then the other side will contain an inert solid like Platinum. The metal on the other side will not be used for both because you want a metal that won't affect the reaction.

Jessica Castellanos

What is the role of a salt bridge?

Jessica Castellanos

To balance redox reactions, you want to balance the electrons transferred in the reduction reaction and the oxidation reaction. To do so, you want to separate the whole reaction into two half reactions: the reduction reaction (gaining electrons) and the oxidation reaction (losing reaction) by writi...

Jessica Castellanos

I don't believe it matters where the cathode and anode are placed as long as you know the direction of electron flow is (from the anode to cathode) or you're writing down the cell diagram setup (like Cu(s)|Cu2+(aq)||Fe3+(aq),Fe2+(aq)|Pt(s)) since the anode is supposed to be on the left side and the ...

Jessica Castellanos

Oxidation number and oxidation state are the same thing, to calculate them there are some patterns like the elements in the first column have a +1 charge, the one's in the second column have a +2 charge, the transition metals vary in charge mostly, the halogens have a -1 charge, column 16 usually ab...

Jessica Castellanos

To balance redox reactions, you want to balance the electrons transferred in the reduction reaction and the oxidation reaction. To do so, you want to separate the whole reaction into two half reactions: the reduction reaction (gaining electrons) and the oxidation reaction (losing reaction) by writin...

Jessica Castellanos

Since the Zn reaction is on the left side, it is the anode so it is going through oxidation (losing electrons), so start off by writing down the reaction for the left hand side as Zn(s) to Zn^2+(aq)+2e- On the right side is the Cu reaction which is the cathode so it is undergoing reduction (gaining ...

Jessica Castellanos

When given the half reactions, you want to balance the atoms on both sides and multiply the half reactions to have equal electrons transferred on both sides of the reaction. When this is done, the half-reactions can be added together to create the net balanced redox reaction. The cell diagram is mai...

Jessica Castellanos

When a system does work, work is positive
When work is done on a system, work is negative

Jessica Castellanos

Can someone explain to me the difference between enthalpy and heat? Are they both transfer of heat?

Jessica Castellanos

What are the three laws of thermodynamics? I was a bit confused when they were mentioned in class.

Jessica Castellanos

I don't see any equation attached to your post you might want to fix it

Jessica Castellanos

By half reactions, Lavelle simply means to separate the oxidation reaction and the reduction reaction to balance one half reaction first, keep track of electrons exchanged and piece it back together with the other half reaction to fully balance the reaction.

Jessica Castellanos

How do you calculate qrev for the equation delta S=qrev/t? Is it usually given or do you need to use other equations based on information given in the question?

Jessica Castellanos

Delta G naught is Gibb's Free Energy with substances in standard state, while delta G isn't. In general, when naught is used, it indicates substance in standard state.

Jessica Castellanos

For transitional metals, the oxidation states usually vary, so for those I would just go off the compound given. However, it would be a good idea to remember some patterns like columns 1 (+1),2 (+2),16 (-2), and 17 (-1).

Jessica Castellanos

I forgot to mention the example in my last post. So for the example in your post, to identify the elements, calculate the oxidation state for each of the elements in the reactants and and for each of the elements in the products and if you use the rules from the previous post you can figure out whic...

Jessica Castellanos

Delta G naught is Gibb's Free Energy at standard state since the degree mark, naught, indicates substance in standard state

Jessica Castellanos

A good way to remember how to identify elements undergoing oxidation/reduction is
"LEO the lion goes GER"
LEO: Losing Electrons=Oxidation
GER: Gaining Electrons=Reduction

Jessica Castellanos

How do you determine which work equation to use based on reversible and irreversible processes?

Jessica Castellanos

What exactly is Gibb's Free Energy? What is it calculating?

Jessica Castellanos

How do you find the value of W?

Jessica Castellanos

Is there any other examples of autoprotolysis other than H20?

Jessica Castellanos

When should you use each of these equations, q=mCdeltaT vs q=nCdeltaT? Is it simply based on the units given or needed in the answer?

Jessica Castellanos

How do you know if a reaction is spontaneous? Do you look at entropy or Gibbs free energy? Both?

Jessica Castellanos

If you look in the textbook page 265 it shows how Cp in monatomic gases is 5/2R and Cv for monatomic gases is 3/2R

Jessica Castellanos

I think, at constant volume and constant pressure, delta U is equal to delta H.

Jessica Castellanos

Will we need to derive the equation w=-nRT(ln V2/V1) or any other equations on the midterm?

Jessica Castellanos

How do you identify conjugate acids and bases in a chemical reaction? How do they differ from their respective acids and bases?

Jessica Castellanos

When discussing the shifts in equilibrium from Le Chatelier's Principle, does this simply mean that the concentration will revert to the same K value or will it obtain a different K value?

Jessica Castellanos

For Kw=1x10^-14, what temperature does this occur?

Jessica Castellanos

Does the 5% rule apply to both chemical equilibrium and acid-base equilibria? Thanks!

Jessica Castellanos

What is the the value of R in PV=nRT? I've seen two different values and don't know which is which.

Jessica Castellanos

When calculating Kp, what unit do you use for the partial pressures?

Jessica Castellanos

Why aren't solids and liquids included in the equation for K?

Jessica Castellanos

During lecture, Lavelle mentioned the delta G equation, but do we need to know this for the chemical equilibrium unit?

Jessica Castellanos

Just to make sure, changing the pressure does affect the way the equilibrium will shift only if the change in pressure is from the change in volume?

Jessica Castellanos

When delta H is positive, is it endothermic or exothermic? And if H is negative?

Jessica Castellanos

How do you identify a polydentate and how many times it can attach itself (bidentate, tridentate etc.)?

Jessica Castellanos

Does anyone know what are the common strong acids and bases we should know for the final?

Jessica Castellanos

How do you identify acidic and basic salts? Is there certain rules?

Jessica Castellanos

What is the difference between coordination compounds and complexes?

Jessica Castellanos

I've been doing all the homework problems and the mini final review that Lyndon posted, both are super helpful for studying acids and bases!

Jessica Castellanos

Does anyone know where the final will be? Lavelle didn't mention it during lecture.

Jessica Castellanos

Hey, I just answered someone else's same question with these definitions of Bronsted Acids and Bases and Lewis Acids and Bases. I hope this helps!

Bronsted Acid: proton donor
Bronsted Base: proton acceptor

Lewis Acid: lone pair acceptor
Lewis base: lone pair donor

Jessica Castellanos

Here are the definitions of Bronsted Acids and Bases and Lewis Acids and Bases. I hope this helps!

Bronsted Acid: proton donor
Bronsted Base: proton acceptor

Lewis Acid: lone pair acceptor
Lewis base: lone pair donor

Jessica Castellanos

If you calculate the pOH with the OH- concentration, you can use the equation pH+pOH=14 to solve for pH. I hope this helps!

Jessica Castellanos

You can calculate the concentration of OH-, higher the concentration, stronger the base. I hope this helps!

Jessica Castellanos

I would suggest just practicing naming coordinate compounds because there are many coordinate compounds but you start to see the pattern after practicing with a couple of coordinate compounds.

Jessica Castellanos

No, as long as the structure is still symmetrical the structure can have lone pairs.

Jessica Castellanos

The Be goes in the middle but there are CH3 on either side of Be so the book is talking about the tetrahedral structure about the carbon atoms instead of the whole structure.

Jessica Castellanos

I always heard that ionic bonds are stronger, ion-ion bonds are stronger than ion-dipole, dipole-dipole, H bonds, London dispersion forces, and dipole-induced dipole as well.

Jessica Castellanos

If you mean covalent radius as tightly bound, HO because O is much smaller than S.

Jessica Castellanos

The net dipole moment is 0 since the dipoles cancel out in an octahedral shape.

Jessica Castellanos

How do you know if a molecule has a dipole?

Jessica Castellanos

Those with high polarizing power are usually smaller cations (top left of periodic table) and those with high polarizability are large anions (bottom right of periodic table). I hope this helps!

Jessica Castellanos

By adding double bonds, the Cl will gain charges which is not favorable because it's not stable, so instead of adding double bonds, I should have lone pairs. Hope this helps!

Jessica Castellanos

For H2S vs H2Se, you should look at the size because the electronegativity of S and Se are really similar but size are very different. For SiH4 vs SiF4, you should look at electronegativity because the big difference in electronegativity of H and F. Hope this helps!

Jessica Castellanos

The shape IO2F2- is a seesaw since its AX4E and I included a link to a picture of the lewis structure as well.

https://www.faidherbe.org/site/cours/dupuis/images4/ax5exem2.gif

Jessica Castellanos

Do we need to know the shape of the s-, p-, d-, or f- orbitals?

Jessica Castellanos

What is the purpose of the Shrodinger Equation? What is it solving for?

Jessica Castellanos

What is a dipole moment? Is that the same thing as a molecule having a dipole? Thanks!

Jessica Castellanos

Can someone explain the difference between electron affinity and electronegativity? Thanks!

Jessica Castellanos

How strong are hydrogen bonds compared to covalent and ionic bonds?

Jessica Castellanos

The valence shell configuration is writing the electron configurations of the outermost electrons the n represents the number for the shells and for the d-block instead of n its (n-1) which is just the pattern of electron configurations. I hope this helps!

Jessica Castellanos

Can someone explain what radicals are and why they're important?

Jessica Castellanos

If you go on the Chem 14A website there's a test and exam schedule pdf with lots of information and it says the midterm is on Nov.6 from 6-8pm but it doesn't say where the midterm is. I hope this helps!

Jessica Castellanos

The valence electrons of manganese is 7 because you add the 2 electrons in the 4s subshell with the 5 electrons in the 3d subshell. Hope this helps!

Jessica Castellanos

The x and y in 2px and 2py refer to the specific orbitals in the 2p subshell that the electrons that are being discussed are in. The professor does seem to prefer this notation but I'm not sure if it's required. Hope this helps!

Jessica Castellanos

Cations are atoms that have lost an electron so they have a positive charge. Anions are atoms that have gained an electron so they have a negative charge. Cations and anions are important because some elements are more stable as ions because they can gain their octet by gaining or losing an electron...

Jessica Castellanos

I think the most important trends to know are electronegativity and ionization energy because it will be important with bonding, but in general you should know the ionic radius and electron affinity trends as well (the trends are pretty similar) just in case there's a question on it. I hope this hel...

Jessica Castellanos

I got the value +9.73*10^-8 m which is UV light. The problem is that you should have made the energy negative since energy is being emitted (the UV light), so the equation you plug in for energy should be -hc/wavelength. Doing this will give you +9.73*10^-8 m. I hope this helps!

Jessica Castellanos

The ionic radius trend does show that anions are greater in size than their grounds state atoms and cations are smaller in size than ground state atoms because they lose electrons. However, for the general trend for atomic radius and ionic radius is greatest towards the bottom left because there are...

Jessica Castellanos

A good question to look at is 1B.15 but the idea is that if a photon hits a metal surface, the work function is the energy required to remove electrons from different metals. This is called the photoelectric effect and the equation is E(photon)- work function = Ek(excess kinetic energy) where E(phot...

Jessica Castellanos

This is actually due to Hund's rule to be more specific about where the electrons in the p orbital would be. Since there are two electrons in the p orbital in your example, they would not both be in the same orbital because that would increase the energy and the lowest energy possible would be with ...

Jessica Castellanos

If there is one electron in the p orbital, we would write that the electron is in the 1px orbital but I think it could be any of the px, py, or pz orbitals but its just the order we write it because we aren't yet able to determine the specific orbital the electron is in, px, py, or the pz orbital. I...

Jessica Castellanos

Hund's Rule says that since electrons repel each other (because they're all negatively charged), electrons in the same sub shell occupy different orbitals with parallel spin to stay at it's lowest energy because the farther away the electrons can be without reaching a high energy is ideal. So when y...

Jessica Castellanos

When we write electron configurations, it is in order of lowest to highest energy and it turns out that 3d is lower energy than 4s, so we put 3d before 4s to keep the pattern of lowest to highest energy going. Hope this helps!

Jessica Castellanos

The work function is how to calculate the threshold energy. The threshold energy is the energy required for an incoming photon to have a greater value of in order to emit energy. Anything less than the threshold energy will not emit any energy. Hope this helps!

Jessica Castellanos

Gamma rays, X-rays, UV light, Visible light, Microwaves is the order with gamma rays at the highest energy and microwaves with the lowest energy. Hope this helps

Jessica Castellanos

What are the differences between the Lyman, Balmer and Paschen series? What does the hydrogen atom have to do with these series? Thanks

Jessica Castellanos

I completely agree with the post before and if it helps, you can think of it with the fact that when we measure the motion of a baseball we don't look at wavelength and frequency like we would with an electron, we instead look at mass and velocity because the wavelike properties of a baseball are un...

Jessica Castellanos

If you refer to your 1D.21 post, the explanation is the same. So you would get the answers, a.) 4p, number of orbitals: 3 b.) 5s, number of orbitals: 1 c.) 6d, number of orbitals: 5 d.) 7f, number of orbitals: 7 (Heres is the explanation again) The n-value stays as is and precedes the letter that in...

Jessica Castellanos

a.) 5d, number of orbitals: 5 b.) 1s, number of orbitals: 1 c.) 6f, number of orbitals: 7 d.) 2p, number of orbitals: 3 The n-value stays as is and precedes the letter that indicates the orbital.The l-value corresponds to a s,p,d or f orbital (l=0 is the s orbital, l=1 is the p orbital, l=2 is the d...

Jessica Castellanos

I agree with the post before that it's the ideas that are important and being able to identify in a situation whether it's precise and/or accurate. Also, I believe the idea you vaguely remember is of error bars (which is shown with a plus or minus of the standard error) and standard error itself. Bo...

Jessica Castellanos

I think your TA was balancing a redox reaction which is a different method of balancing reactions that uses oxidation numbers to balance chemical equations due to the amount of electrons lost and gained in the reaction that need to be accounted for and balanced. If that's the case and you need help ...

Jessica Castellanos

I can't seem to find the problem, but the amount of sig figs is determined by the sig figs of the amount given (by the given amount with the least sig figs), so although you may get a number with less sig figs when you do your calculations you should refer back to the given amounts. So maybe the boo...

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