CHEMISTRY COMMUNITY

Brianne Conway 1D

If you're given a list of experiments which correspond to certain reactant concentrations, you pick which experiments to compare based on which reactant's concentration is being held constant. If there are two reactants and you're trying to determine the order of the first reactant, you would pick t...

Brianne Conway 1D

I'm pretty sure it's talking about when a metal electrode is oxidized to form metal cations, which will dissolve into solution. So I guess you'd just have to look at the half-reactions and see which metal is being oxidized.

Brianne Conway 1D

Not next quarter, but I'll be taking 14C and 14BL over the summer.

Brianne Conway 1D

I was wondering this too, thank you guys for clearing that up.

Brianne Conway 1D

An intermediate is a species that is produced in an elementary step and consumed in a subsequent elementary step. So an intermediate doesn't appear in either the reactants or products in the overall equation.

Brianne Conway 1D

The forward and reverse reactions follow the same energy pathway except in reverse, so when a catalyst lowers the activation energy for a reaction is makes it so both the forward and reverse reactions need less energy to proceed, meaning they will both go faster.

Brianne Conway 1D

Thank you! Good luck to everyone!

Brianne Conway 1D

deltaU is 0 in an isothermal reversible expansion since the energy lost through work is replaced by heat from the surroundings, meaning q = -w.

Brianne Conway 1D

What seems to work the best for me personally is redoing textbook problems, going over homework problems, watching Khan Academy videos as review, and rewatching Lavelle's lectures and/or rereading the textbook for certain topics I don't feel too confident on. Hope this helps and good luck on the fin...

Brianne Conway 1D

I was wondering about this too. In the textbook it says the reactant of the each half-reaction should come before the product, but the textbook answers don't even seem to consistently follow that so I'm not too sure.

Brianne Conway 1D

The question says to balance the skeletal equations by using oxidation and reduction half-reactions (all the reactions take place in acidic solution). The equation in part d is the reaction of chlorine in water: Cl2(g) -> HClO(aq) + Cl2(g). I was wondering if there's possibly a typo in this question...

Brianne Conway 1D

Yup, that's how I've always thought of it.

Brianne Conway 1D

qrev is the amount of heat generated in a reversible process. So does deltaS = q/T only apply to reversible expansions and compressions? I believe you use this equation when you are at a constant temperature for a reversible process. So then to clarify, when it's an irreversible process and the tem...

Brianne Conway 1D

I think it just means that you should know the basics of how the formulas for change in energy and change in entropy are derived from the 1st and 2nd laws of thermodynamics, since both of those are ultimately derived from the basic premises of the first two laws of thermodynamics. I wouldn't worry a...

Brianne Conway 1D

I'm pretty sure that's generally how you would do it. I was watching some Khan Academy review videos today and in one of them the guy said you need to calculate how much heat is required to first bring the substance up to the boiling point (or melting point), and then calculate how much heat you nee...

Brianne Conway 1D

Let's take all the bad chemistry jokes and Barium.

Brianne Conway 1D

Let's take all the bad chemistry jokes and Barium.

Brianne Conway 1D

I'm out of chemistry jokes, I should zinc of a new one.

Brianne Conway 1D

I'm out of chemistry jokes, I should zinc of a new one.

Brianne Conway 1D

I tell bad chemistry jokes because all the good ones Argon.

Brianne Conway 1D

I try to tell chemistry jokes but there is no REACTION.

Brianne Conway 1D

Two chemists walk into a bar. One tells the bartender, "I'll have an H2O." The other says, "I'll have an H2O too!" The second chemist dies.

Brianne Conway 1D

Why should you go drinking with neutrons? Because wherever they go, there's no charge!

Brianne Conway 1D

Why does a hamburger have less energy than steak? Because it's in the ground state!

Brianne Conway 1D

I tell bad chemistry jokes because all the good ones Argon.

Brianne Conway 1D

I try to tell chemistry jokes but there is no REACTION.

Brianne Conway 1D

Two chemists walk into a bar. One tells the bartender, "I'll have an H2O." The other says, "I'll have an H2O too!" The second chemist dies.

Brianne Conway 1D

Why should you go drinking with neutrons? Because wherever they go, there's no charge!

Brianne Conway 1D

Why does a hamburger have less energy than steak? Because it's in the ground state!

Brianne Conway 1D

The book very briefly touched on this, but I was wondering if anyone could explain what the difference is between bond enthalpies and bond dissociation energy.

Brianne Conway 1D

I'm not entirely sure but I think I remember Lavelle saying that we wouldn't need to know how to solve cubic equations for ICE tables since K would be small enough to approximate x if we even received a problem with a cubic equation. However, I noticed on outline 1 that it says we should know how to...

Brianne Conway 1D

Both of your answers helped to clear that up; thank you!

Brianne Conway 1D

Yes concentration changes anytime the quantity stays the same and the volume changes or vice versa. However, if you were to increase pressure by adding an inert gas, concentration does not change since the number of moles and the volume stay the same.

Brianne Conway 1D

I guess this doesn't necessarily apply to simple math or calculator errors, but it's a good idea to write out units when doing calculations to make sure you have the correct values for whatever units you need. I know Lavelle sometimes likes to throw in questions where you need to convert units first...

Brianne Conway 1D

I'm not entirely sure but I believe in the book in the table of K values they had a column labeled just as "K" and another column labeled as "Kc" so I guess if it's just K it's referring to Kp.

Brianne Conway 1D

you can find it on Sapling under Resources. It is a PDF called "Atkins 7e SSM".

Brianne Conway 1D

a vapor becoming a liquid does not need energy to form bonds; forming bonds always gives off energy. this isn't necessarily related to your question, but it might help clarify: an endothermic reaction doesn't mean that it requires energy to form the bonds, it means that the energy required to break ...

Brianne Conway 1D

Just to clarify, if a question says a reaction is at equilibrium and then asks about the effect of changing the partial pressure of one of the products/reactants, would that not affect the overall pressure of the reaction vessel? For example, question 5J.9 in the textbook gives the equation 3NH3 + 5...

Brianne Conway 1D

Yeah, so the R is used in the ideal gas law equation PV=nRT, because while PV is proportional to nT, it is the R value that makes the whole ideal gas equation true and helpful for calculations. Now the units for R can be many different things such as J/K·mol, L·atm/K·mol, L·bar/K·mol, and L·Torr/K·...

Brianne Conway 1D

I noticed that on the equations and constant sheet, there are two values of the gas constant, 8.314 J mol-1 K-1 and 0.08205 L atm mol-1 K-1. I was confused about how to know which one to use because in my discussion section the TA used the first one but with the units of the second one. I thought yo...

Brianne Conway 1D

I'm a first year and I hadn't taken a chem class since junior year of high school either. For me personally, Khan Academy is a good way to learn and review chemistry topics. That's what helped me get through AP chem haha.

Brianne Conway 1D

Why did the white bear dissolve in water? Because it was polar!

Brianne Conway 1D

Why does a hamburger have less energy than steak? Because it's in the ground state!

Brianne Conway 1D

Why does a hamburger have less energy than steak? Because it's in the ground state!

Brianne Conway 1D

To add on to what Mikayla said, the concentrations of the gases that were already in the container stay the same, but altogether there will be more moles of gas in the container since an inert gas was added. That's why the pressure increases even when the volume stays the same, because if you look a...

Brianne Conway 1D

I like to watch Netflix, cuddle with my cat, and read. I also play the piano every once in a while or do cross-stitching or knitting, but unfortunately I haven't had a lot of time to do those things recently.

Brianne Conway 1D

I like to watch Netflix, cuddle with my cat, and read. I also play the piano every once in a while or do cross-stitching or knitting, but unfortunately I haven't had a lot of time to do those things recently.

Brianne Conway 1D

I like to watch Netflix, cuddle with my cat, and read. I also play the piano every once in a while or do cross-stitching or knitting, but unfortunately I haven't had a lot of time to do those things recently.

Brianne Conway 1D

I definitely learned from my mistakes in 14A and have changed my study habits for this quarter. Going to the UA workshops and step up sessions are super helpful and it's something I totally regret not starting earlier last quarter!! Same, I never went to any of the sessions last quarter but I'm gon...

Brianne Conway 1D

I definitely learned from my mistakes in 14A and have changed my study habits for this quarter. Going to the UA workshops and step up sessions are super helpful and it's something I totally regret not starting earlier last quarter!! Same, I never went to any of the sessions last quarter but I'm gon...

Brianne Conway 1D

Hi! I was wondering how everyone will be studying for the final. Since it will be cumulative I don't know where to start studying. Does anyone have any tips? Thank you in advance! Hi, personally, I didn't study incredibly well last quarter and did worse than I wanted to, so this quarter I'm trying ...

Brianne Conway 1D

For those textbook problems, I drew out the Lewis structures and looked for atoms that had lone pairs. For example, for water, the oxygen has lone pairs, so it can be a monodentate ligand (it's not a bidentate ligand because the two lone pairs are on the same bonding site). At the UA session earlie...

Brianne Conway 1D

As others have said, lone pairs are spread out more since they are not held between two positively charged nuclei. So if an atom has a lone pair the bond angles will be slightly less than the normal angles for that shape. You don't need to know the exact angle, just that it will be slightly less due...

Brianne Conway 1D

Hi! So I like to calculate how many valence electrons I should have and then count the electrons again to make sure that I have drawn the lewis structure correctly. Also calculate the formal charges and remember you want the most stable/less charged structure. However, if you do have a charge like ...

Brianne Conway 1D

I thought Dr. Lavelle said soft water is more alkaline and that's why it feels soapy, but when I looked it up it says hard water is more alkaline because it has more minerals in it, so I'm really not sure anymore.

Brianne Conway 1D

Steph Du 2B wrote:If the bond being broken for the compounds you are comparing is different, you compare bond length (ex. HCl and HBr). If the bond being broken is the same, then you compare electronegativity (ex. CCl3COOH and CH3COOH).

Thanks for that explanation, it really clears everything up nicely.

Brianne Conway 1D

I was wondering this as well and here is what I found online: "Radial node is a spherical surface where the probability of finding an electron is zero. The number of radial nodes increases with the principal quantum number (n). Angular node is also called a nodal plane. It is a plane that passe...

Brianne Conway 1D

Happy late Thanksgiving! Our family doesn't really have a special tradition other than eating dinner together with my grandparents and watching football, but that's good enough for me :)

Brianne Conway 1D

I was wondering about this too, but I don't think it matters too much since you're still able to determine the formula of the molecule.

Brianne Conway 1D

To determine if a ligand is polydentate and to specifically find how many places it can bind, do you have to draw the Lewis structure or is there some other intuitive way of knowing how many lone pairs it has? Asking because textbook exercise 9C.5 lists ligands and asks to identify which can be poly...

Brianne Conway 1D

Dr. Lavelle said in his lecture that you can write it either way.

Brianne Conway 1D

I did slightly better on this midterm than the last. When I was looking at my grade for the second midterm though, I realized that the grade shown in the Grades tab on CCLE was the number of points out of 110 rather than the percentage, meaning I actually did worse on both midterms than I initially ...

Brianne Conway 1D

Yes, the coordination number is the number of bonds.

Brianne Conway 1D

It's asking for exactly what it says, M is an unknown metal whose ground-state electron configuration is given and we need to figure out what element M is. So you basically need to work backwards from how you normally would write an element's electron configuration. Just count the number of electron...

Brianne Conway 1D

1 is incorrect because fluorine actually has a smaller atomic radius; atomic radius decreases across a period due to higher effective nuclear charge. 4 is incorrect because oxygen and fluorine both have the 1s and 2s orbitals filled, so the 2p orbitals in both of them experience the same amount of s...

Brianne Conway 1D

The bigger the atom is the more polarizing power it has, because it has more protons pulling on the electrons. Hence, Be would be the smallest and lowest, then Rb, then Sr. This means polarizing power goes up across a period and increases as u go down a group. It's true that a cation with a higher ...

Brianne Conway 1D

Hydrogen bonds form between a hydrogen attached to a highly electronegative atom (N, O, or F) and another N, O, or F on another molecule.

Brianne Conway 1D

I don't think we actually need to be able to determine if an electron is spin-up or spin-down; we just need to know +1/2 is spin up and -1/2 is spin down and that two electrons in the same orbital can't have the same spin state.

Brianne Conway 1D

Open the LockDown Browser and in the upper left corner there's a button that has an i in a circle. Press on that and a box will pop up with a button in the middle that says "Check for newer version". Press on that and it'll say get newer version or something like that; press on that button...

Brianne Conway 1D

Induced dipole induced dipole interactions occur in all molecules whether they are polar or nonpolar because induced dipole induced dipole refers to temporary fluctuations in electron density that cause dipoles to form. Thus, induced dipole induced dipole interactions occur in all molecules since al...

Brianne Conway 1D

I personally don't have any significant studying techniques. I just take notes on stuff mentioned in lecture that is new to me and/or that seems important. Additionally, I just make sure to do the homework and all of the textbook problems for practice and obviously go over problems I miss and try to...

Brianne Conway 1D

Yes, that is correct. That's why in his lecture Dr. Lavelle showed examples of how molecules with the same molecular formula but different shapes can have different boiling points, since molecules of certain shapes have stronger induced dipole induced dipole interactions than others (which would inc...

Brianne Conway 1D

Van der Waals interactions are induced dipole induced dipoles. They are just temporary fluctuations in electron density that can cause dipoles to form, leading different molecules to be attracted to each other.

Brianne Conway 1D

Just as you said, permanent dipoles are from two atoms having different electronegativities (thus one atom will always be partially positive and the other partially negative). On the other hand, induced dipoles are temporary fluctuations in electron density that randomly cause dipoles to form.

Brianne Conway 1D

I was about to ask this too, unfortunately I guess we can't review them. :/

Brianne Conway 1D

I was wondering this too and couldn't figure out where I'm supposed to click on my name, but I noticed that if you look at one of your posts, on the right hand side it says how many posts you've made, so as long as you have 5 posts per week you should get full credit.

Brianne Conway 1D

I don't think we need to actually "determine" any of the quantum numbers, we just need to know what they mean. So you just need to know that +1/2 is spin-up and -1/2 is spin-down.

Brianne Conway 1D

I was also wondering about this because I remember learning about electronegativity but not electron affinity when discussing periodicity in high school chem, but now we only talked about electron affinity and not electronegativity. Also, they sound pretty similar, but I am not sure if they are the ...

Brianne Conway 1D

Yes you can have the same 3 quantum numbers since each orbital can hold two electrons. Thus, two electrons in the same orbital would have the same first three quantum numbers but have a different spin state.

Brianne Conway 1D

n2 represents the excited state the electron is in, while n1 represents the energy level that the electron returns to. n2 is always greater than n1. I may be wrong, but that's the way I think about the Rydberg Equation. Yeah, that's what I realized is probably the case as I thought about it more, w...

Brianne Conway 1D

I'm kind of confused about the Rydberg equation v=R[1/n1^2 - 1/n2^2]. When doing problems involving emission spectrums, my TA did 1/nfinal - 1/ninitial, but the n1 and n2 make it seem like you would subtract the final energy level from the initial energy level. Are you just supposed to subtract the ...

Brianne Conway 1D

You're right in that 6.001 x 10^-7 m converts to 6001 angstroms. You shouldn't be multiplying by 10^-10 though since you're not actually converting between different units. They're both in meters, just in different forms of scientific notation, if that makes sense. Basically all you need to do is th...

Brianne Conway 1D

Since the problem asks for the maximum wavelength that will reject electrons, KE=0, so the work function is equal to the energy of the photon. Therefore, you can set 4.810 x 10^-19 J equal to hv. Since we want to find wavelength, you can make v=c/lambda, making the equation 4.810 x 10^-19 J=hc/lamb...

Brianne Conway 1D

Like Mohamed said, for questions like this that ask for the minimum uncertainty of something (whether it be position or velocity), you just need to know how to rearrange the ΔxΔp ≥ h/4π equation to solve for what you need. For questions that ask about an electron, a proton, or a neutron, the mass is...

Brianne Conway 1D

I think on a test it might be considered wrong since Lavelle explicitly stated it is written the second way since it shows that the 3d orbital is lower in energy than the 4s orbital once the 4s orbital is full.

Brianne Conway 1D

"The value of the Rydberg constant R∞ is 1.0973731568508 × 10^7 per metre. When used in this form in the mathematical description of series of spectral lines, the result is the number of waves per unit length, or the wave numbers. Multiplication by the speed of light yields the frequencies of t...

Brianne Conway 1D

I don't think we need to know how to actually determine it; I'm pretty sure that has to do with Schrodinger's equation. We just need to know which number signifies which spin.

Brianne Conway 1D

Like Rose said, m sub l ranges from l to -l. That way, there are enough different values of m sub l to signify each configuration for each type of orbital. For example, for an s-orbital (l=o), m sub l can only be 0, signifying the only configuration for the s-orbital. For a p-orbital (l=1), which ha...

Brianne Conway 1D

I don't know why the first electron in an orbital is specifically spin-up, but I'm pretty sure they occupy different orbitals before filling them up because of the repulsion forces between them, so they'd want to be as far away as possible and thus occupy different orbitals.

Brianne Conway 1D

I'm pretty sure if a problem asked for the quantum numbers of an electron it would tell us whether it was spin-up or spin-down. +1/2 signifies spin-up, while -1/2 signifies spin-down.

Brianne Conway 1D

In the photoelectric experiment, they had initially assumed that light acted as a wave, so when electrons were not initially ejected, they expected that increasing the intensity of the light would cause electrons to be ejected since increasing the intensity would increase the energy of the light if ...

Brianne Conway 1D

If you go up to Figure 1C.4, there is a paragraph above that figure and then an equation above that paragraph. That is Equation 4, the equation they're talking about in step 1. Equation 4 is simply derived from Equation 3, which you'll find if you go up a little more; it's right above the green subt...

Brianne Conway 1D

6.022x10^23 is a constant that can apply to anything, it's just an easier way of describing quantities of atoms or molecules without having to work with big, complicated numbers. Pretty much how kilo- means 1000 of whatever it is you're working with (grams, meters, etc.), a mole is just 6.022x10^23 ...

Brianne Conway 1D

I might be wrong, but I think I remember my TA saying that partial credit would be available; however, if the midterm actually is going to be multiple choice I'm not sure how that would work. You should ask your TA.

Brianne Conway 1D

We're supposed to have our webcam pointing down at our work and have our hands in view at all times. So to do this you can either have an external webcam that you can point down toward your desk while being able to still see your screen (if you're using a laptop). Or, you can use a separate monitor ...

Brianne Conway 1D

If you're talking about how he switched the -4.09x10^(-19) to 4.09x10^19 I'm pretty sure it's because the negative represents the energy the electron lost, meaning that the electron would release a photon with that amount of energy (a positive value) because of the law of conservation of energy. So ...

Brianne Conway 1D

I always wait to round till the very end and make sure I'm using correct significant figures for my end answer. Dr. Lavelle may have another method but this is what I was taught in high school. Regarding different numbers on the periodic table, I'd use the periodic table in the book considering it ...

Brianne Conway 1D

As everyone else said, I think it would be easier to just convert it to integers, but if you like to leave it with decimals you probably can as long as the question doesn't actually ask for the empirical formula.

Brianne Conway 1D

I could possibly be wrong here, but I think that leading zeros are the zeros that do not count. For instance, 0.034 would have only 2 sig figs, whereas 0.304 would have 3 sig figs since the zero second zero is in the middle and not leading. However, I am a bit rusty on sig fig rules, so feel free t...

Brianne Conway 1D

I'm pretty sure there can only be one limiting reactant because either one reactant will limit the other(s) or the reactants will all be present in proportionate amounts according to the chemical equation in which case they would not limit each other. The only case I can think of where there might b...

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