CHEMISTRY COMMUNITY

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I just came to ask about this question-- does anyone know how we derive this formula? I was looking at the equations we are given, and I couldn't make sense of how molar kinetic energy is equal to 3/2RT. Thanks in advance!

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I've also been struggling with this problem, and I've found that drawing out the Lewis structures correctly is usually the hardest part! But it definitely helps to visualize which bonds are broken and formed between the reactants and products.

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I was also wondering why we always subtract the enthalpy of vaporization. Some of the equations for the formation of the species have the species in its liquid state as a product; since we're concerned about the liquid state of the species, why do we still subtract the enthalpy of vaporization? And ...

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I don't have the answer for you and I was equally confused at this problem, but I just wanted to reply and say I'm laughing so hard at you saying "all I got was people saying 'yeah me too' so I'm not gonna post my answer". (Also wanted to keep track of this post to see when someone replies...

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Hey! - You're gonna want to find the equilibrium quotient, Q, using the partial pressures and concentrations given in the problem. The equation is [concentration of products] ^ stoichiometric coefficients / [concentration of reactants] ^ stoichiometric coefficients, excluding solids and liquids (inc...

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I'm a little confused about the question because I don't remember exactly what this question asks off the top of my head, but I know that the two equations you've written here will both end up with charges balanced and a net 3+ on both sides of the one equation? If that helps

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You get the right answer if you use the logQ equation instead of the lnQ equation but I have no idea why it would matter either way. Yeah I'm kind of confused about why exactly we'd need to use one equation rather than the other? The only guess I have is like if we're finding hydrogen ion concentra...

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Erxn is Estandard at equilibrium. Q=1 at equilibrium. This checks out mathematically using the equation Estandard=Erxn+rt/nf lnq. if q=1, then lnq=0 and Erxn=Estandard I'm probably about 50% confident in my claim here but I feel like Q doesn't always have to equal 1 at equilibrium. Doesn't it just ...

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Why is it that in part b, the solution manual says that E cell not and E cell are both temperature dependent? Shouldn't E cell not only be at 25 degrees Celsius? How is it temperature dependent then? What you're saying makes sense, because standard cell potential (Ecell°) takes places at standard c...

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There are homework problems assigned that ask to find the half reactions and balance the equation (such as 4 and 11), which doesn't (as far as I know; please correct me if I'm wrong!) necessarily require one to find the standard reduction potential of that reaction. However, the standard potential ...

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When balancing redox reactions, if they dont tell you whether or not it is in acidic or basic solution, can you choose to add OH- or H+ to balance as you please? Or do you always have to assume it will be acidic and use H+ to balance the hydrogens? I don't know if there will ever be a need for assu...

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For the reduction reaction of P4 --> 4PH3 Why do I not add an H2O on right side (the side that is reduced state) just like it did in all the previous problems You don't need any more H's on that side in order to balance that equation! That's why you wouldn't need an H2O. :) I was super confused abo...

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I am having trouble identifying the reducing and oxidizing agent in equations such as 3a in the homework? What's been easiest for me is to think that the oxidation state goes down-- i.e., is being reduced-- in the elements that are being reduced (the oxidizing agents). So if the oxidation number go...

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I was stuck too and I keep getting 2649813.982. Is that what you’re getting as well? The value you're writing here is 2.65 x 10^6, I don't know if that clarifies anything because the problem isn't written here and I don't have my book in front of me so I'm coming at this out of context haha but I h...

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siannehazel1B wrote:I understand how to plug all the values into the NERNST equation after I write the half reactions, but I'm confused as to where the solutions manual is getting 0.025693V/n. I thought we were supposed to use either 2.303RT/nF or 0.0592/n?

.025693 V is R * 298.15 K / F.

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I don't know why, but 2-3 is my go-to. Like I'll do 1.2 x 10^5 or 1.23 x 10^5 or whatever. It doesn't seem to be a huge deal on exams, just follow the number of sig figs in the other values you're given. :)

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Liam Maxwell 2E wrote:I had a similar problem when calculating this problem I got n=2 because the balanced equation is H2=2H+ +2e but the solution manual said n=1

Which question are you referring to? I feel like I had a similar problem.

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A pH meter is a device used to measure the pH of a solution/system. So yes, it follows that the question you're referring to is wanting you to find the pH! It would help more if you would provide the question you're trying to answer.

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If Q>K then that means there is more product than at the equilibrium concentration. As such, LeChatelier's principle tells us that the reactants will be favored. If Q<K then that means there is more reactant than at the equilibrium concentration, so the products will be favored. Yep! Q just has to ...

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The half-reactions given in the appendix of the textbook give the reduction reaction. Since the anode is where oxidation takes place, we would need to flip the half-reaction given in order to get the oxidation half-reaction. The cathode is where reduction takes place, so no such flipping is needed....

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I don't know the problem off the top of my head and I don't have my book on me, but balancing Hydrogen in basic solution is done by adding H2O to one side and OH- on the other. In acidic solution, H+ is added to one side and H2O to the other. So if the reaction in this problem takes place in a basic...

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Yeah, I'm assuming that since it was always given to us in the book's homework problems, it'd always be given to us on a test!

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inert metal | reactant | product || reactant | product | inert metal The anode is typically on the left and the cathode is typically on the right. The double line represents the salt bridge, and will be replaced with a single line if there is a porous disk instead of a salt bridge. Lines are used t...

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Are you referring to delta u in an isothermal reaction? This is because for an ideal gas U = 3/2 nRT. Therefore, if the moles of gas stay the same, n is constant, R is the gas constant, and if T is constant (which is what isothermal means) then U is constant which means delta U = 0. Sorry, do you m...

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Aijun Zhang 1D wrote:When the pressure is constant, we use w = -Pext $\Delta V$

When temperature is constant (isothermal), we use w = -nRT ln (Vfinal/Vinitial)

Are these the only two scenarios we'll likely be dealing with? Thanks!

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As we know, a negative delta g correlates with spontaneity. While it seems logical to assume the more spontaneity means more randomness and therefor less stability of the compound, however when the free energy is more spontaneous then there reactants will change into more products that are essentia...

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Vincent is correct, but the next steps are as follows... There's a wonderful bit in the book about this exact scenario: "Finding entropy of transition at another temperature." We must follow 3 steps: 1. Heat the liquid to its normal boiling point. 2. Allow it to vaporize. 3. Cool the vapor...

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The consensus appears to be that we use R for non-ideal gases and Cp or Cv for ideal gases. Should we expect to be told whether or not to assume ideal behavior for the gases in the problems?
Thanks!

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I think an important delineation to make is whether or not you're referring to entropy (S) or change in entropy (ΔS). Entropy in its absolute value is calculated by using the Boltzmann equation, S= k ln W. In terms of entropy in its absolute value (calculated through the previous equation), no, nega...

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Delta S= q/T

Convert the temperatures to Kelvin in order to yield a result in Joules per Kelvin (per second)!
The value of q is given in Joules in the problem. Just divide by the Temp. in Kelvin. The second part of the problem, then, is just conversion from seconds to days.

Hope this helps!

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Entropy of a system can be defined as being the thermodynamic quantity that demonstrates how a system's thermal energy cannot be converted into mechanical work. Usually it is interpreted as being the degree of disorder or randomness in a system. Could you elaborate more on this? I think I understan...

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Yes, entropy is an extensive property, that is correct!

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Hello,

I'm not sure I'd be able to recognize what the standard state of a given element is. Is that something we'd be expected to be able to do? I know that carbon is graphite, for example, but aside from that, I'm not sure.

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Hess's law takes into account step reactions-- reactions where the products of one serve as the reactants of the next. The addition of these step reactions (and subsequently, their corresponding enthalpy changes) lead to a reaction which includes the reactants and products with which we are interest...

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I can't speak to whether or not this material will appear on test one, but it's a fairly straightforward definition in my opinion:
Adiabatic walls are thermally insulating and heat cannot be transferred across them.
Diathermic walls do allow the transfer of heat across them.

Hope this helps.

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So it can be at any temperature, so long as the substances are existing in their standard state? Thanks!

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I believe that it will be evident which method should be used based upon what is given in the problem.

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From my understanding, the reactions that are given will always be able to be added (whether the direction needs to be reversed or not) to yield the desired reaction. Hope this helps!

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Sarah's answer is great. I have in my notes that amphoteric means that it can react with both acids and bases, whereas amphiprotic means that it can act as a proton donor or a proton acceptor (a Bronsted acid or a Bronsted base, respectively). I may be wrong, but I'm getting that Sarah's answer desc...

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Hi!
Oxoacids are acids containing oxygen. I may be wrong, but I believe include hydrogen as well.

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Elizabeth Bamishaye 1E wrote:Electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels, so you would complete the orbital until moving on to the next.

Yes, so spin-pair in the s-orbital and then parallel spins in the p-orbital before spin-pairing in the p orbital. (Right?)

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Hi! Please correct me if I'm wrong, but whether or not a molecule is bent (referred to as angular in the textbook) depends on the presence of lone pairs on the central atom. A lack of lone pairs will allow the bonded electrons to be further apart, as in the linear structure, and a presence of lone p...

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Molecular Orbital Theory gives us more understanding of molecules we may not be able to know just through Lewis structures. It mainly gives us context on bond strength and magnetic properties. We can figure out the bond order through MO theory, and the higher the bond order, the stronger the bond. ...

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So is it correct to say that sigma bonds involve s-orbitals and pi bonds involve p-orbitals?

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These terms stand for "Highest Occupied Molecular Orbital" and "Lowest Unoccupied Molecular Orbital."

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I'm also having trouble determining whether a molecule is polar or nonpolar-- I realize the directionality of the charges are important, but that's what I have trouble determining. Should I refer to Chapter 3 for help with this? Thanks!

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Agreed, I think it's important to note that bond angles will be smaller than expected in species with lone pairs because the lone pair-lone pair repulsion as well as the lone pair-bond repulsion will be stronger than any bond-bond repulsion, and therefore the bonds are forced closer to one another t...

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Hi! Most helpful to me has been that the hybridization depends on the shape. So tetrahedral shapes will have a certain hybridization, as will linear, octahedral, trigonal bipyramidal, et cetera. So writing the Lewis structure would be a great first step!

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Thus far, I have been calculating formal charge on the central atom each time with a single versus a double bond in order to determine which would be the more stable structure. I feel like there's an easier way to do this. How does looking at valence electrons factor into it? In other words, how do ...

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I just did a problem where Cl was given 12 valence electrons-- is this possible because it is in the 3rd period? And is there a way to determine the limit of how many electrons can be added to those atoms with expanded valence shells?

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Yes! Their quantum numbers produce a unique fingerprint :)

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Are there any other instances in which there is a higher n value that has a lower amount of energy? Hope my phrasing makes sense.

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And a further question-- what is meant by the subscript x, y, and z (used today in lecture when forming the configuration for O)? Are these related to the subshell?

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Could someone explain to me the difference between these three (orbitals, subshells, and shells)? Obviously a subshell is a part of the shell, but then is is the shell a part of the orbital or vice versa? Just confused on the terminology. Thanks in advance! :)

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It does! Thank you so much!

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The question asks what the wavelength of the ejected electron is with a velocity 3.6x10^6 m/s. I used the deBroglie equation wavelength=h/mv, so I plugged in Planck's constant divided by the mass of an electron times the velocity given. My calculator gave a value of ~2619. The solutions manual lists...

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This refers to the value of n for the lower energy level. For the Lyman series n=1 at the lower energy level, for example. In all honesty I don't know what these lines mean/their importance, so I am wondering that as well?

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This is in reference to question 1.27 on the homework: I don't understand how the answer is reached. The question asks how many photons can be generated in 2.0 seconds by a lamp with 32 W that emits violet light at a wavelength of 420 nm. The solutions manual calculates the energy per photon and the...

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Hi all, I am confused about the process of using combustion analysis to determine molecular formula. It's been awhile since I've taken high school chem! Could somebody please explain how combustion analysis works (even a broad explanation is fine-- I'd just like to hear it in someone else's words ra...

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The reactant that is in excess will not be consumed entirely in the reaction, whereas in theory the limiting reactant will be consumed entirely and there will be nothing left over. The amount of product formed is based on how many moles you have of the limiting reactant-- however many moles you have...

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