CHEMISTRY COMMUNITY

Kyle Walsh 2J

Hi! I'm pretty sure that you're correct, delta S of the surroundings only equals zero for isothermal, irreversible free expansions. Since the enthalpy change is zero, so is the change in entropy. Hope this helps!

Kyle Walsh 2J

Hi, so I know that there is an intersection between thermodynamics and kinetics, because both determine whether or not a reaction happens, but I'm still confused conceptually on what exactly this means, and when which is used. Prof. Lavelle briefly mentioned it in the beginning of the kinetics secti...

Kyle Walsh 2J

Hi! As said by Chanel, a reaction is spontaneous when its delta G is negative, and same goes for delta G naught. The only difference being that delta G naught only applies to reactions that are at standard conditions. Hope this helps!

Kyle Walsh 2J

Hi! I'm pretty sure that the flow of electrons in a galvanic cell will always be from anode to cathode, unless outside energy is put into the system to reverse the flow. However, the only spontaneous current occurs from anode to cathode (conventionally, left to right). Hope this helps!

Kyle Walsh 2J

Hi! I believe that the molecularity of the slow elementary step will always exactly match the rate law, as both the molecularity and rate law are only concerned with the species that affect the reaction in any given step. Therefore, I'm pretty sure intermediates would be ignored in both. Hope this h...

Kyle Walsh 2J

Hi, I was just wondering if we are expected to know how to determine the rate law or approximate it using graphs of concentration like the one that Prof. Lavelle used on his first lecture on kinetics. I know that it can be done, but I wouldn't know how to go about it. Any help is appreciated, thanks!

Kyle Walsh 2J

Hi! Yep, I'm pretty sure that all open systems are assumed to have constant pressure because any change in pressure is so much smaller when compared to the surroundings of the system. Hope this helps!

Kyle Walsh 2J

Hi! Basically as I understand it, the graphs are representations of the derivative at a certain point of the reaction. If the graph is linear, it means that there is only one slope value, giving the definitive slope for that instantaneous point. Whereas if the graph is not linear, it means that ther...

Kyle Walsh 2J

Hi! I believe sometimes we are asked to be able to identify the catalysts/intermediates in reactions when we aren't explicitly given them (or they aren't written above the reaction arrow). I'm pretty sure that Sapling question #18 deals with this topic, so that could be more specific practice. Hope ...

Kyle Walsh 2J

Hi! I believe the largest difference is the fact that galvanic cells are spontaneous, while electrolytic cells require an outside energy source to push a redox reaction in the reverse direction. In galvanic cells, chemical energy is being converted to electrical, while in electrolytic cells, electri...

Kyle Walsh 2J

Hi! I was just looking over the end of the last lecture and the two types of catalysts seemed to be important. Is there any effects of each one that I should explicitly know about when it is involved in a reaction? Will we be asked to identify which of the two types is more effective in a given scen...

Kyle Walsh 2J

Hi, I was just wondering if anyone had a brief explanation or outline of what the steady-state method for determining reaction mechanisms looks like, as we didn't cover it much in lecture and I'm was curious. Thanks so much!

Kyle Walsh 2J

Hi! This isn't super technical, but my favorite tool when discussing Le Chatelier's principle is the phrase "towards what you take, away from what you add". This works in nearly every situation, even applying to endothermic and exothermic reactions if you can visualize which side the heat ...

Kyle Walsh 2J

Hi, so in high school chemistry I was taught that to balance basic reactions you went through the same steps as an acidic one, but then just added as many OH- as H+'s, and then cancelled out the water. However, in the solutions manual, I often notice that they have a different, more streamlined meth...

Kyle Walsh 2J

Hi! What I like to do is first find two experiments where one concentration is being held constant and the other is changing. Then, I look at by what factor the non-constant concentration is changing, which is usually doubling. I then look at the rate for the given reactions and compare. If the rate...

Kyle Walsh 2J

Hi! I believe it depends on what topic is being considered, but for almost everything outside of ideal gases, standard temperature refers to 298 K. Hope this helps!

Kyle Walsh 2J

Hi! Basically, since the question tells you that the half life changes when the concentration does, you know it is either zero or second order, and then from there you just see if it is directly or inversely proportional. Since the half-life increases as the concentration decreases, it is inversely ...

Kyle Walsh 2J

Hi! I believe that in order to solve for the unknown you just take the equilibrium reaction and isolate HClO. And as for the water, the solvent is never included in the rate law. I know I'm a bit late to this one, but I hope this helps anyways!

Kyle Walsh 2J

Hi! I think it's always good to know how to convert between different units, just in case they are asked for. Obviously, in homework and elsewhere, atm is used far more often than torr, but it could be valuable nonetheless, and it's a relatively simple conversion. Hope this helps!

Kyle Walsh 2J

Hi, I was just curious as to what specific qualities electromotive force has when compared to cell potential, as I have it written down in my notes but not much context as to the definition. Thanks!

Kyle Walsh 2J

Hi! So basically a porous disc is just a membrane that allows the anions of a cell to transfer directly between solutions, whereas a salt bridge uses a salt. For example, a porous disc allows the direct transference of Cl- ions, while a salt bridge requires NaCl to transfer the Cl-. As far as I can ...

Kyle Walsh 2J

Hi! I don't believe that phases matter in the order that compounds are written in, especially because phases in the textbook problems were kind of all over the place. Hope this helps!

Kyle Walsh 2J

Hi! In all of the examples given in the textbook, I believe that it was identified for us, but it can also be found manually if you have the overall rate law of the reaction. In that case, you'd just have to calculate the rate laws of each step individually and then see which one matches up. Hope th...

Kyle Walsh 2J

Hi! I think the key difference here is between the rate and the rate constant. The rate of the forward reaction is equal to k (the rate constant) times the concentration of both of the reactants, and the same for the reverse reaction, its rate constant and the products. Therefore, the rate constants...

Kyle Walsh 2J

Hi, I was just confused as to how to get started on this problem, I even looked at the hints for it and it still didn't make sense. I think I'm just overlooking a small crucial piece of information, but anything helps. I copied the problem below for convenience. Thanks! A certain reaction has an ent...

Kyle Walsh 2J

Just as Sara said, you would use the equation work is equal to the negative of external pressure times the change in volume. In other words, w=-P(ex)ΔV. Hope this helps!

Kyle Walsh 2J

Hi, I was just wondering how to get started on question 20 for this week's homework, I'm still pretty fuzzy on the whole delta U stuff. I copied the question below for convenience. Any help is appreciated, thanks! "A 0.201 mol sample of N2(g) initially at 298 K and 1.00 atm is held at constant ...

Kyle Walsh 2J

Hi! I'm also not sure if this was gone over in lecture, but I found a website that summarizes the derivation pretty well. Hope this helps! "If the gas expands reversibly, the external pressure ( pext ) can be replaced by a single value ( p ) which represents both the pressure of the gas and th...

Kyle Walsh 2J

Hi! I think the reason sapling usually asks for you to convert L*atm to Joules is because Joules is the standard unit for work. Hope this helps!

Kyle Walsh 2J

I believe this has to do with the fact that isothermal expansion is using energy to increase the volume. If heat is applied during isothermal expansion, the volume increases instead of the temperature. Hope this helps!

Kyle Walsh 2J

In the lecture, Lavelle showed us an infinite sum formula and then showed an "equivalent" integral that is supposed to convey the same thing (calculating the work of expansion). I was just curious if we need to know the sum formula, and if there are any instances where we would use that in...

Kyle Walsh 2J

Any help on how to start this problem would be appreciated, I don't really understand work calculations at all. I copied it below for convenience. Thanks! Automobile airbags contain solid sodium azide, NaN3, that reacts to produce nitrogen gas when heated, thus inflating the bag. 2NaN3(s)⟶2Na(s)+3N2...

Kyle Walsh 2J

Yes, aqueous solutions are always included in the K for a given reaction. Hope this helps!

Kyle Walsh 2J

I believe that it's not the pressure that affects gas reactions, it's the volume changing. But the pressure change is just a byproduct of the changing volume.

Kyle Walsh 2J

Hi, I was just wondering if anybody could help me get started on this problem, I know it has something to do with specific heat capacity but the equation doesn't quite work. The question is: If you combine 290.0 mL of water at 25.00 ∘C and 110.0 mL of water at 95.00 ∘C, what is the final temperature...

Kyle Walsh 2J

I try to think of it as finding the strong cation/anion, as there is a much smaller list of strong acids/bases as compared to weak ones. If the cation is from a strong base, then it's basic, if the anion is from a strong acid then it's acidic, and if they're both from strong acids/bases then it is n...

Kyle Walsh 2J

For endothermic processes, I tend to think of them as something that requires energy. Baking a cake requires energy from you, but a car using gasoline doesn't require energy, it produces it in the form of heat. Ice melting requires heat, or else it wouldn't melt, but water condensing doesn't require...

Kyle Walsh 2J

I believe we'd just find the standard enthalpy in a list or index that was given to us. From what Lavelle was saying, we won't usually have to convert the molecule to a different form, but even if we do, then you just add the enthalpy of vaporization if it's a liquid, or enthalpy of melting and vapo...

Kyle Walsh 2J

In Lecture, Lavelle mentioned that water vaporization has a large enthalpy value due to the hydrogen bonds. I don't entirely understand this, because then why is the enthalpy value of ice melting still relatively small? Why does the bond type only affect vaporization?

Kyle Walsh 2J

So I remember seeing more complicated examples of Hess's law equations in high school chemistry where equations were multiplied by 1/2 or 1/3, then flipped, then added together, etc. I know that when multiplying the coefficients, you multiply the delta H by the same factor, and flipping the equation...

Kyle Walsh 2J

Hi! Total pressure is just the combined pressures of each of the gases in a given reaction. To find total pressure at equilibrium, you would simply add up the equilibrium pressures found through an ICE table. Hope this helps!

Kyle Walsh 2J

Hi! The reaction quotient Q is found using the same formula as K (products/reactants) and is more of a symbolic shorthand to show that this reaction is not at equilibrium and is instead at a random point in it's reaction. So long story short, for this question you would just plug in the concentratio...

Kyle Walsh 2J

Hi! While I do think that the theory behind your question is accurate, I doubt any questions about this would ever be asked. Just from a practical standpoint, why would you add an excess of a low density solid as opposed to just changing the volume of the reaction vessel otherwise. The solid would h...

Kyle Walsh 2J

Hi! I can't say for sure that we need to know it since I'm not the one designing the course, but my guess would be it never hurts to know, especially if there is a curveball question on a test.

Kyle Walsh 2J

Hi! I don't remember if this type of question was covered, but I don't seem to have any notes on it and I'm kinda just lost on how to get started. Any help is appreciated, and I copied the question below for convenience. Thank you! Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g...

Kyle Walsh 2J

So, I remember using the line "away from what you add, towards what you take", when discussing Le Chatelier's Principle in high school chemistry, and it seems that it still holds true now. However, Lavelle emphasized that we should have a deeper understanding, and I still don't exactly get...

Kyle Walsh 2J

Fancy seeing you here. I believe that it's not possible for Q to be smaller than K while [P] is greater than [R], because Q is equal to [P]/[R]. Meaning that when [P] is greater than [R], Q is going to be some number over 1, whereas K would be 1, as [P]=[Q] for K.

Kyle Walsh 2J

I believe that the unit is mol*L^-1, which is just another way to say mol/L, or M. He might have just had a typo in the slides or something.

Kyle Walsh 2J

Solving for the concentration at the end should not affect results, as long as the ICE table is set up correctly and you plug in the equilibrium concentrations.

Kyle Walsh 2J

Hi! I believe that adding an inert gas does not change the concentrations of the reactant or product because it doesn't react with any part of the equilibrium reaction, which is just a property of inert gases. I believe the reason Lavelle brought this up in lecture was to highlight that you can't al...

Kyle Walsh 2J

Fancy seeing you here. I'm pretty sure that this is a correct assumption, but it's important to note that there is a difference between compound surface area and atom size. Since an increase in atom size means an increase in bond length, this weakens the bond and overall strengthens the acid. Hopefu...

Kyle Walsh 2J

Hi! So in this question, B(OH)3 is acting as the Lewis acid, as it is accepting the electron pair from the (OH)- to turn into B(OH)4-. You can double check this by confirming that H30+ is formed, meaning that the original compound was acidic and the conjugate is basic. Hope this helped!

Kyle Walsh 2J

Hi! I'm pretty sure you're exactly right, and this is just a textbook error. I found an old archived post on this from a while back, which I'll link below, and it basically just confirms what you're saying. Hope this helps!

viewtopic.php?f=41&t=1024

Kyle Walsh 2J

Hi! So you're actually most of the way solved with the problem conceptually already, the 1 and 2 are just the energy levels of the orbitals, as those are the outermost shells for each atom and therefore where hybridization occurs. For example, carbon's outermost shell is the 2p orbital, and that's w...

Kyle Walsh 2J

Hi! I'm pretty sure this and buffers in acid/base reactions is a chem 14b topic that we won't be tested on this quarter.

Kyle Walsh 2J

Hi! Sigma bonds are the weaker and more flexible of the two, allowing for rotation of bound atoms, and are bound end-to-end. The overall strength of a pi bond is much higher, and therefore does not allow for rotation of the bound atoms, and pi bonds are bound side-by-side. In addition, pi bonds are ...

Kyle Walsh 2J

Hi! So to find the pH from the concentration of H+ ions, you just need to take the -log[H+]. Then to find pOH you take 14 and subtract the pH that you found from the first step. Finally, to find the concentration of OH- ions, you convert the pOH that you found from a log into the concentration (whic...

Kyle Walsh 2J

Hi! I don't believe polarity is directly tied to hybridization, rather both of these are characteristics of the shape of a molecule. Hybridization is determined by how many lone pairs/bonds are attached to the central atom, which then gives a molecular geometry, and from there, polarity can be deter...

Kyle Walsh 2J

Hi! So I'm not sure if this has been discussed before, but I was just wondering how to determine whether a salt is acidic or basic as asked in the Sapling HW for this week (their examples were NH4ClO4, Na2S, K2SO3, KCl, and LiClO4). I might just be misremembering but I don't recall this being covere...

Kyle Walsh 2J

Hi! So the majority of the time, these titrations only work because you can experimentally determine when the solution is an acid or a base, either through an indicator or some other form of pH test. For every titration, you will know the whether it the solution starts as an acid or a base because t...

Kyle Walsh 2J

Hi! So a similar question was asked at a bit ago and there are some pretty thorough explanations there. Hopefully this helps!
viewtopic.php?f=62&t=70283

Kyle Walsh 2J

Hi! So how I approached this problem was to first determine whether the cation or anion was the weak acid/base based on what was told to us in lecture. So for part a) I chose C6H5O- as the weak base in water because Na+ won't affect pH as a group one element. Then, I just wrote out the reaction that...

Kyle Walsh 2J

So for weak/strong acids, there is actually a list of defined strong acids, HCl04, HBr, HI, HCl, HNO3, H2SO4, and all the rest are considered weak acids. As for stability, the stronger an acid is, the more stable it will be. Determining the relative stability of individual weak acids can be done by ...

Kyle Walsh 2J

Hi! Since individual ions can be considered Lewis acids/bases themselves, these pairings to the outer atoms should be considered as well. For example, ZnCl2 is considered a Lewis acid, because the Zn can accept protons, but the individual Cl- ions are also considered Lewis bases, as they are donatin...

Kyle Walsh 2J

So as I understand it, the hydrogen atoms in H2CCCH2 are actually perpendicular, as the pi bonds from the double bonds on each side of the central C are perpendicular to each other. This is contrasted with H2CCH2, which only has one pi bond, so it has to lie in the same plane. Then for H2CCCCH2, the...

Kyle Walsh 2J

Hi! So, basically electron geometry is the arrangement of the electrons in a molecule, whereas the molecular geometry is the actual shape. The notable difference here is that lone pairs do not affect the electron geometry, whereas they definitely do affect molecular geometry. As for how to find it, ...

Kyle Walsh 2J

Hi! I believe that this molecule is nonpolar because every atom has the same polarity (as they are all oxygen), and they are all evenly spaced in a tetrahedral formation (since there are no lone pairs), and therefore their dipoles cancel. Hope this helped!

Kyle Walsh 2J

Hi! I was rereading my notes on this section and realized that I was somewhat unclear on what I wrote down, especially like the actual applications of intermolecular forces and why they matter in general chemistry. I know the general trends in strength, but what effect does the strength have in the ...

Kyle Walsh 2J

Hi! I was just curious as to if the type of bond (i.e. pi or sigma), can be determined purely from the shape of the molecule, or if you need to draw out the Lewis structure every time. I might just be forgetting but I can't remember if this was discussed. Thanks!

Kyle Walsh 2J

Hi! So I'm still not entirely clear on why hybridization occurs. I understand that it is necessary to explain the experimentally determined structures of molecules, but there must be some natural process that causes hybridization to occur. If not, is hybridization merely a thought process used to ex...

Kyle Walsh 2J

So I remember from high school chemistry that polarity can be determined by using molecular geometry, but since we haven't learned that yet, I am still a little confused as to how to determine polarity with just what we know. I'm pretty sure Dr. Lavelle went over this in the lectures, but it isn't r...

Kyle Walsh 2J

Hi! Yes, H-bonding occurs when another compound has lone pair of electrons AND when the H atom is already bonded to an N, O, or F atom. The compounds that could have H-bonds are anything that satisfy these requirements. Some examples include molecules like chloroform (CHCl3) and ammonia (NH3) and ov...

Kyle Walsh 2J

Hi! I'm pretty sure that these are just polyatomic ions with set numbers of oxygens that we could be expected to just memorize. I believe nitrite is 2 oxygens, nitrate is 3 oxygens, phosphite is 3 oxygens, and phosphate is 4 oxygens. Hope this helps!

Kyle Walsh 2J

Hi! To determine the number of valence electrons, you have to use electron configurations and add the electrons of the outermost shell. For example, for Mn, the electron configuration is [Ar]4s2 3d5. If you turn this into Mn4+, then the electron configuration is [Ar]4s2 3d1, since a charge of 4+ mea...

Kyle Walsh 2J

Hi! So basically there are two types of exceptions to the octet rule, atoms that take less of an octet and atoms that can take more than an octet. The ones that take less than an octet are very situational, but obviously hydrogen and helium are the clearest exceptions, and then other row 2 elements ...

Kyle Walsh 2J

So I was looking over the Sapling HW, the half that is covered in week 4, and question 9 addresses the oxidation number of a chlorine. I might just be misremembering the terminology, but I don't recall ever learning how to find the oxidation number of an atom. It's probably really simple, but any he...

Kyle Walsh 2J

I don't know if anybody else has said this already, but Hollywood on Netflix is an absolute must watch. It was created by Ryan Murphy, the same guy who did Glee and the Politician, another solid Netflix show, so you know it's good.

Kyle Walsh 2J

Hi! So the main differences between ionic and covalent bonds include the sharing of electrons, ionic bonds being electrostatic in nature due to charge differences, and solubility. I'm not sure we can entirely answer this until we get deeper into this topic, but yes, I would assume that since electro...

Kyle Walsh 2J

Hi! Yes, high polarizability and highly polarizable mean the same thing for an anion. As for effective nuclear charge, yes, the lower the polarizability of an anion, the greater the effective nuclear charge. However, in general for an overall molecule, polarizability is determined by the difference ...

Kyle Walsh 2J

In today's lecture (11/6), Dr. Lavelle was talking about how you should determine whether a given molecule has covalent or ionic bonds using electronegativity, and then draw it accordingly. This seems to imply there is a difference in how ionic and covalent Lewis structures are drawn, but I thought ...

Kyle Walsh 2J

The problem states: The E.coli bacterium is about 2.4 μm long. Suppose you want to study it using photons of that wavelength or electrons having that de Broglie wavelength. What is the energy E(photon) of the photon? What is the energy E(electron) of the electron? I got the correct answer for the fi...

Kyle Walsh 2J

During today's lecture (10/30), Lavelle had multiple points about how H, He, Li, and Be are all exceptions to the Octet Rule. I vaguely remember this from high school chem, but I don't remember the reasoning at all. Why are they exceptions? Thanks!

Kyle Walsh 2J

Hi! I believe that in the lecture Dr. Lavelle was referring to using the electron configurations, which are just numbers we have to memorize. s shells take 2 electrons, p shells take 6 electrons, d shells take 10 electrons, and f shells take 14 electrons. I don't believe you can determine the exact ...

Kyle Walsh 2J

Hi! I think that this is up to the professor, but in general, lines are only used for bonds and lone pairs are represented by pairs of dots. Otherwise it could get a bit confusing.

Kyle Walsh 2J

Hi! I believe that in the lecture, both of these terms were used to describe the same group of noble gases. However, in general chemistry the difference is that inert gases can be compound gases, the only requirement being that their outermost electron shell is filled. Noble gases are all purely ele...

Kyle Walsh 2J

So I know that Dr. Lavelle said we won't be responsible for the mathematical side of electrostatic potential energy, but I'm still a bit confused as to the theoretical side. Why is it important at all? Does it relate to bond strength or something that will be covered later? Thanks!

Kyle Walsh 2J

Hi! The Lyman and Balmer series just have different wavelength ranges associated with them, and unfortunately I think that's something we just have to memorize. I believe Lyman is 94-122 nm while Balmer is 410-656 nm. You could also figure out what series it is if a type of light is given, as Lyman ...

Kyle Walsh 2J

Hi! The x,y,z planes are only used in the context of modelling an orbital in a 3d space. They are purely conceptual, because we don't know the true form of an electron or orbital, so we make 3d models out of their respective wave functions. Whether a part of the "orbital" modelled is in th...

Kyle Walsh 2J

Hi! In my experience, different textbooks and teachers prefer rounding done different ways, but it is always a safe bet to just round at the end.

Kyle Walsh 2J

Hi! I believe your method isn't outputting the same answers because since it is an electron, not a photon, you can't use E=hv to determine frequency and then wavelength.

Kyle Walsh 2J

Hi! I'm pretty sure that E=hv is a universal equation that works whether the electron is emitted or incoming, but many problems phrase it as an incoming electron because that is how it is perceived to monitoring devices in a lab.

Kyle Walsh 2J

You can find the energy of the incident photons by using the standard energy equation, E=hc/lambda, where Planck's constant is 4.1357E-15 eV/s and the speed of light is 3.00E17 nm/s. Then you just subtract the energy of the ejected electrons from the energy of the incident photons.

Kyle Walsh 2J

Hi, I was starting the Sapling hw for this section, and I'm a bit conceptually confused about number 5. The problem is: "The electron in a hydrogen atom is excited to the n=5 shell and emits electromagnetic radiation when returning to lower energy levels. Determine the number of spectral lines ...

Kyle Walsh 2J

Hi! I'm not one hundred percent sure but I don't believe that a question will ask for any other type of uncertainty, as the Heisenberg uncertainty principle is only able to be applied to particles. There are similar principles in physics that can be applied to objects other than particles, but those...

Kyle Walsh 2J

Hi! I'm pretty sure that emission of energy always means that n2 is going to be 1, because the energy is emitted when the energy level decreases. The energy level increases when energy is being absorbed, and decreases when it's being released, much like exo/endothermic reactions.

Kyle Walsh 2J

In high school chemistry we learned multiple different types of chemical reactions and how to write/balance each one, such as decomposition, combination, single/double replacement, and combustion. I was wondering if it's implied that we should know these already, as it seemed that way for combustion...

Kyle Walsh 2J

Hi! So for this problem I used the same standard dilution equation as the others, with the small twist being the doubling volume. If you set up M1V1=M2V2, you get the initial molarity as 0.10 M, and the initial volume as 10 mL, or 0.01 L. We're solving for the final molarity so you can leave that be...

Kyle Walsh 2J

Hi! I totally forgot how to read this stuff too at first lol. Essentially each line has a carbon attached on either end, which is then satisfied by hydrogens. The amount of hydrogens attached is 4 minus however many bonds are connected to the given vertex. So for example, the first diagram with the ...

Kyle Walsh 2J

You only need the molar masses and volumes to solve, I'm pretty sure what's given is balanced.

Kyle Walsh 2J

Part A of question E23 on the review HW reads "Calculate the amount (in moles) of (a) Cu2+ ions in 3.00 g of CuBr2". Originally I calculated the mass percentage of Cu, then multiplied that by 3.00 g to find the grams of Cu, and then divided it by the molar mass of Cu to find the moles of C...

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