CHEMISTRY COMMUNITY

Jessica Chen 2C

Yes, a cell can be both a galvanic and a concentration cell, as long as the concentration cell is spontaneous and can produce electrical energy via its redox reactions.

Jessica Chen 2C

Yes, it just specifies that it's the delta G of an ionization reaction.

Jessica Chen 2C

If it's a concentration cell, adding water will affect the concentration, and that will in turn affect the voltage.

Jessica Chen 2C

it is also important to know the difference between gradual expansion and sudden expansion, in which you would apply the appropriate formula. The questions I have seen typically state whether the process is occurring gradually or suddenly. Hope this helps! Sorry, could you explain what the appropri...

Jessica Chen 2C

I’m not 100% sure but I think they mean that you should always check that the rate law has the same order. When using K to find concentrations for intermediates, it can be easy to make mistakes while substituting, so just check that it’s done right by making sure the order matches.

Jessica Chen 2C

Electrochemistry! I think I dreaded it going into it because I always found it confusing before, but I put extra effort into studying and understanding it before Test 2 and now it’s the topic I’m the most comfortable with haha.

Jessica Chen 2C

n=1 because the coefficient of every reactant/product is 2 so you divide the entire reaction by 2 to simplify, leaving you with 1 e-.

Jessica Chen 2C

If you flip the sign then you add the cell potentials; if you’re subtracting then just use the given reduction potentials without flipping.

Jessica Chen 2C

Yeah I guess the pseudo rate constant allows us to focus on seeing how one specific reactant’s concentration affects rate. By making the concentration of A super high, it’s essentially not changing as the reaction proceeds, and thus we can include it in k’.

Jessica Chen 2C

For the question that asks for what’s wrong with the cell diagram, how is it possible for the left side to only have solids? Don’t you need some form of aqueous solution in a cell?

Jessica Chen 2C

Changing the mass of the electrode shouldn’t affect cell potential, it will just affect the lifespan of the electrode.

Jessica Chen 2C

Thanks for the response! Could someone summarize what knowing the type of system would tell you for each system? Like if it’s an isolated system, do I know that a certain value would be 0 or something?

Jessica Chen 2C

For the question on slide 5 of the final review PowerPoint, why do we only use the delta G for PCl5 and PCl3 when calculating the delta G of the reaction?

Jessica Chen 2C

While I was reviewing I watched a few videos that stated the first law as delta u= q - w, and they said that w is positive when work is being done on the surroundings. It threw me off because it’s different from how we’ve been thinking about it, and now I’m confused. How are we treating w on the tes...

Jessica Chen 2C

What type of problems could be asked regarding the different types of thermodynamic systems? Like, would there be a question focused solely on this concept, or are they just mentioned as part of a different type of problem?

Jessica Chen 2C

We can also look at the reduction potential values for each half reaction to determine which side the electrons should be on for each half reaction. We want Ecell to be positive (in order to be spontaneous) so the more positive reduction potential is the reduction half reaction (with electrons on th...

Jessica Chen 2C

I don't believe we will need to know the specifics about liquid mercury as an electrode for the final, as it is a more complex case and he said the test would be pretty straightforward.

Jessica Chen 2C

Both equations have to have the same number of electrons being transferred, that's a part of balancing redox reactions. So you'd multiply the Ag half reaction by 2, and n=2 for both equations.

Jessica Chen 2C

Since we're already here.. could someone briefly explain what Downs Process is? I'm curious, I don't think I've heard about it before.

Jessica Chen 2C

Yes, it would be useful to be able to derive, we might need it to solve a problem.

Jessica Chen 2C

I just want to confirm because I was a bit confused: the units for rate are always the same, but units for rate constants can change depending on the order of the reaction?

Jessica Chen 2C

In redox reactions (ie. Zn + 2H+ → Zn2+ + H2), the ion from the oxidation half-reaction (the anode) is a product (Zn2+), and the ion from the reduction half-reaction (the cathode) is a reactant (H+). In Le Chateliers principle, when you increase the concentration of reactants or decrease the concent...

Jessica Chen 2C

Always add H2O first to balance out any O in the reactions. Then, depending on whether it's in acidic or basic solution, add H+ or OH- (and H2O on the other side to balance O) in order to balance out the H.

Jessica Chen 2C

I agree with all the previous responses, and it makes sense if you think about the meaning of these values. Ecell can describe spontaneity (spontaneous if the value is positive, not spontaneous if the value is negative) while K, the equilibrium constant, describes whether the reaction is product or ...

Jessica Chen 2C

Does anyone know if we have to write the concentration of aqueous solutions for cell notation problems on Test 2?

Jessica Chen 2C

C(gr) is carbon in the form of solid graphite and is commonly used as an inert electrode.

Jessica Chen 2C

One thing that's useful for understanding the effect of concentration cells is Le Chatelier's principle. In redox reactions (ie. Zn + 2H+ → Zn2+ + H2), the ion from the oxidation half-reaction (the anode) is a product (Zn2+), and the ion from the reduction half-reaction (the cathode) is a reactant (...

Jessica Chen 2C

To add on to this, we can calculate the cell potential under nonstandard conditions using the Nernst equation.

Jessica Chen 2C

I don't believe there's a difference between using graphite vs platinum as an inert electrode, although we did hear a bit more about platinum in class, so that's the one I default to.

Jessica Chen 2C

First of all, remember the reducing agent is the one being oxidized, so you have to flip the given standard reduction potential equation to get the standard reduction potential of the oxidation half-reaction. When calculating the reduction potential of the cell, we want the value to be positive beca...

Jessica Chen 2C

How do you identify the oxidizing agent or the reducing agent? Is it typically on the left or right side of a chemical reaction?

Jessica Chen 2C

This question asks us to balance the redox reaction of chlorine in water, with the reaction being Cl2 gas going to HClO and Cl2 gas again. How would you go about starting this? I'm having a hard time identifying the oxidation half-reaction and the reduction half-reaction.

Jessica Chen 2C

I agree with the previous response. If you think about it, it makes sense because you're changing the coefficient of each reactant/product by the same factor, and the coefficients determine what power the values are raised to. For example, if the overall reaction is multiplied by 2, then each reacta...

Jessica Chen 2C

How do you find the net charge of an acid given the pH and the pKa?

Jessica Chen 2C

To be at maximum entropy is to be at the “most random” state. That’s not the best wording but I think Dr. Lavelle’s example in class is helpful: if he opened a sealed beaker of argon gas in the lecture hall, it would diffuse and spread through the entire room until it was at maximum entropy.

Jessica Chen 2C

You need to add the energy required to melt the ice cube to the energy required to raise the temperature of the (liquid) water in order to get the total energy that needs to be used in this process.

Jessica Chen 2C

If you're asking if the final equilibrium value of HI is 2(60% of H2 + 1.60 mol of I2), then no, that's not entirely correct. When you set up an ICE table, you can see that for the "C(hange)" row, the change in the value of HI is +2*x because there are two moles. To find x, you use the fac...

Jessica Chen 2C

Could someone please explain the difference between thermochemistry and thermodynamics? I'm a bit confused about the distinction.

Jessica Chen 2C

I agree with what the previous reply said. In these types of problems, it's important to keep track of the signs of the values. A negative w value means the system is performing work on its surroundings, while a positive w value means the surroundings are performing work on the system. Likewise, a n...

Jessica Chen 2C

Wait, when did everyone get their tests back? We didn't get ours during our last discussion...

Jessica Chen 2C

Why is enthalpy a state function, but not heat? I understand how a property like distance isn't a state function, but it's harder for me to understand with heat.

Jessica Chen 2C

It's easier to determine the strength with the Ka or Kb values, the concentration can't really tell you much about how much the acid/base dissociates.

Jessica Chen 2C

I agree with the previous response, you do [A-]/[HA], and then x100 to get the percentage.

Jessica Chen 2C

The test covers up to acids & bases (so outline 1 & 2), and I'd recommend being very comfortable with ICE tables.

Jessica Chen 2C

Kw=1x10^-14 at 25*C.

Jessica Chen 2C

When it comes to the partial pressure of a reactant/product changing, you can basically think of it as a change in concentration. So if the partial pressure of a reactant increased, then the reaction would shift to the right/to the products. But if they're talking about the pressure of the reaction ...

Jessica Chen 2C

Yes, if you approximate for a small x value (when K<10^-3), you have to check that the value of x is less than 5% of the initial concentration in order for the approximation to be valid.

Jessica Chen 2C

I think it's atm or bar, but keep in mind that Kp itself won't have units.

Jessica Chen 2C

Since you know 60% of H2 reacted, you know 40% is remaining at equilibrium. Thus, you can find the equilibrium value of H2 by multiplying the initial value of H2 by 0.4.

Jessica Chen 2C

If they ask for the "equilibrium composition", that's generally an indication to use an ICE table. Also, if they ask for K and they give some initial values and some equilibrium values, you should probably use an ICE table to find all the equilibrium values to calculate K.

Jessica Chen 2C

I think section 5H.2 in the textbook on composite reactions is helpful in understanding how to do this problem. Basically, in 5H.3, the reaction they give us is a composite reaction, and we have to use Table 5G.2 to find the two reactions that are added together to make the reaction we're given. Onc...

Jessica Chen 2C

How do we determine when we can use the "x is small" approximation? Do we look at the value of K for this?

Jessica Chen 2C

How do we determine when we should use Kp versus when we should use Kc? I find myself defaulting to Kc, only to find that the answer is given in Kp.

Jessica Chen 2C

Does anyone know when we'll get our final grade? Do we have to wait until we pick it up winter quarter?

Jessica Chen 2C

I'm a bit confused about the pH for row i). I plug the given H30+ concentration, 1.50 M, into the pH equation, so -log(1.50 M)= -.176, but the answer should be .176 according to the solutions manual. What is going on?

Jessica Chen 2C

What are the most important biological examples that we should know for the final?

Jessica Chen 2C

How can we tell if an atom goes through hybridization or not?

Jessica Chen 2C

Yeah, basically all elements period 3 and beyond can disobey the octet rule because they have room in the d-orbitals of their valence shell.

Jessica Chen 2C

I'm a bit confused by the mixed answers too, I put 8 and got it right on my test. There were 4 N with 1 lone pair each, so that's 4 hydrogen bonding sites; there were 2 O with 2 lone pairs each, so that's another 4 hydrogen bonding sites, giving me 8 in total. In theory, if there were any H attached...

Jessica Chen 2C

We use bis-, tris-, etc. when the ligand's name already contains di-, tri-, etc, or when the ligand is polydentate.

Jessica Chen 2C

This is pretty helpful, thanks for sharing! Does anyone happen to know which definition is used most commonly, and why?

Jessica Chen 2C

How can you tell if an acid/base will dissociate into ions in water?

Jessica Chen 2C

How do you tell if it's the cation or the anion that's going to be involved in the proton transfer with the water?

Jessica Chen 2C

I think you have to write the atomic symbols of the ligands in alphabetical order, at least according to Toolbox 9C.1 in the textbook.

Jessica Chen 2C

Molecular shape is the shape we get while looking mostly at the bonds (I say 'mostly' because lone pairs do affect molecular shape), while electronic geometry considers both bonds and lone pairs in the shape. Thus, electronic geometry only has the basic shapes (ie tetrahedral, trigonal bipyramidal, ...

Jessica Chen 2C

I also have trouble asking questions sometimes. I've found that one good way to come up with questions is having Chemistry Community open while doing homework, and making a post when I get really stuck on a problem. Also, I'll correct my homework, and if I don't understand why I got something wrong,...

Jessica Chen 2C

In the case of coordination compounds, the coordination number is simply the number of ligands attached to the central metal. We can find it by looking at the subscripts of the ligands. [Co(CN)5(OH2)] has a coordination number of 6: 5 CN + 1 OH2

Jessica Chen 2C

We use brackets around the complex, which is the entire species with the central metal ion and the ligands. We use parenthesis within the brackets, around any ligands that need it. For example, there's [Fe(CN)6]; the whole thing in brackets is the complex, and the parenthesis are around the ligand, ...

Jessica Chen 2C

I think Dr. Lavelle said radicals are treated as one region of electron density when it comes to determining shape.

Jessica Chen 2C

In VSEPR notation, there are 3 symbols you need to know: A - the central atom; X - bonded atoms; and E - lone pairs. Then you look at the Lewis structure, see how many bonded atoms and lone pairs there are, and write those numbers in the subscripts by their symbols. For example, H 2 O is AX 2 E 2 , ...

Jessica Chen 2C

Keep the electronegativity trends in mind: F is the most electronegative atom, so as you move away from F on the periodic table, the atoms become less electronegative. Since Ba is further from F than Be is, Ba is less electronegative than Be. This means that the electronegativity difference between ...

Jessica Chen 2C

I think cations tend to be better at polarizing atoms than they are at being polarized, and vice versa for anions, which is why we tend to talk about cations in terms of their polarizing power and anions in terms of their polarizability. If cations have polarizability and anions have polarizing powe...

Jessica Chen 2C

First we add up the valence electrons, and we find that we have 16 electrons to work with. We know N is the central atom because it has lower ionization energy than O. So we start off with N-N-O. We could use all the electrons to complete the octets for the outside N & O, but then we see that th...

Jessica Chen 2C

It's kind of similar to why Cr and Cu have electron configurations different from what we expect - stability. It is more stable to have those 3 half filled orbitals in nitrogen than it is to have 1 pair of electrons, and then two unpaired electrons like in oxygen. Since it wants to be more stable, i...

Jessica Chen 2C

Orbitals aren't actual physical "places" for electrons to stay in, they just describe the probability of finding an electron in a specific region. So if an electron isn't "in" an orbital, that orbital doesn't exist, because the probability of finding an electron there is zero.

Jessica Chen 2C

I don't think so. I don't believe we've learned how to do that, or if that's possible? Maybe just keep in mind how the size/charge of the atom affects polarizability and polarizing power.

Jessica Chen 2C

I think it will typically be given to us. Perhaps in some cases, with common substances like water, they might give us a temperature and expect us to know the state. Otherwise, I'm pretty sure we aren't expected to know this? Maybe look at bond strengths, and just know that the stronger the intermol...

Jessica Chen 2C

Larger atoms have higher polarizability not only because their electrons are more loosely held, but also because the larger area makes it more feasible for many electrons to gather at one end of the atom, creating a more noticeable polarity than smaller atoms.

Jessica Chen 2C

What exactly do we need to know about wave functions for the midterm? I'm a bit confused about it. Will we have to use Schrodinger's equation?

Jessica Chen 2C

Covalent bonds are typically between two nonmetals (right side of periodic table), while ionic bonds are between a metal and a nonmetal, so be sure to keep that in mind too!

Jessica Chen 2C

What is an easy way to remember the trends of polarizability/polarizing power on the periodic table?

Jessica Chen 2C

Do you think we have to write out the entire equation for formal charge on the midterm? Or can we just calculate it in our head, and write the formal charge by the element? I don't want to spend too much time writing out work if it's unnecessary. Thank you!

Jessica Chen 2C

Why do we take electrons from the s orbital rather than the d orbital? As in, why is the Ga3+ ion [Ar]3d^10 rather than [Ar]3d^8 4s^2?

Jessica Chen 2C

In the solutions manual, for questions that require us to arrange atoms in order of increasing/decreasing radii or ionization energy, it gives us the actual radii/ionization energy in parenthesis. Are we required to actually know any of these? Or just have a general idea of the size of atoms/ionizat...

Jessica Chen 2C

Can someone explain why Na has a smaller first ionization energy than Al? Their valence electrons are both the first electrons in a subshell (3s1 vs 3p1).

Jessica Chen 2C

For Mn, why is an electron removed from the 4s orbital to form a +1 ion, rather than the 3d orbital?

Jessica Chen 2C

I also got (n-1)d3ns2, and the solutions manual I checked says that this is correct.

Jessica Chen 2C

How can you tell that a) and b) are in the excited state? I can see that c) is excited and d) is in the ground state, but I'm not sure how the first two are.

Jessica Chen 2C

I like to go about this by first associating the letter with its orbital angular momentum quantum number (l). So s -> l=0, p -> l=1, d -> l=2, and so on. Then compare that number to the first number, which is the principal quantum number (n). We know that l must be less than n, so if the second numb...

Jessica Chen 2C

So I looked back at my test to check what I did for this problem, and I realized that I can't seem to find this question on my test. I guess this means there's different versions of the test out there? (Also, based on what you've said for the question, I think you could also convert from 5 grams of ...

Jessica Chen 2C

I know we didn't have to end up reporting the difference as a percentage of the wavelength of the neutron because the wavelengths were the same at 3 significant figures, but if we did, how would we go about doing that?

Jessica Chen 2C

Why is the uncertainty in velocity 5 m/s when given 5.00 ± 5.0 m/s, when in the example in the text they gave ±1.00mm/s and had the uncertainty as 2mm/s?

Jessica Chen 2C

I just directly plugged the frequency they gave us in part b into the c=λν equation, but that's not correct. How do we know when we have to take kinetic energy into account as well?

Jessica Chen 2C

Thanks for the replies! The equation needed wasn't in section 1A, but then I realized it was one of the first things to show up in 1B ^^|| I'll be sure to remember the equation from now on!

Jessica Chen 2C

The question is "which of the following happens when the frequency of electromagnetic radiation decreases?" And I picked (c) "The extent of the change in the electrical field at a given point decreases" by process of elimination, because I knew the other answers weren't correct. ...

Jessica Chen 2C

I think in order to solve this problem, you have to be able to recognize that UV radiation is in the Lyman series and therefore n1=1.

Jessica Chen 2C

I know we use wavelength x frequency= c to convert between frequency and wavelength, but what equation do we use to find the energy of the photon? I can't seem to find it in the text.

Jessica Chen 2C

Yeah, I agree with the others, you can have it in either moles or grams since it won't affect the final answer. Unless the question specifically asks for the amount of product in grams, I find it easiest to just leave it moles for the sake of finding the limiting reactant.

Jessica Chen 2C

Actually, I think the book uses c to represent molarity and M to represent molar mass in equations. I was a bit confused by this too, since M is the symbol for units in molarity (ie .5 M). So in the equation m=cMV, it's basically mass=molarity x molar mass x volume.

Jessica Chen 2C

In order to solve these problems, I went through a (probably unnecessarily) long process of first finding the mass percentage of the ions, multiplying that number by the mass, dividing that by molar mass to get moles, and then adding up all the moles if necessary, before finally dividing by volume t...

Search found 103 matches