CHEMISTRY COMMUNITY

lilymayek_1E

basically; you have to remember that solid and liquids are not used in Q or K calculations, which is where they try to trick you!

lilymayek_1E

the reason Br- doesn't need to be included is that it is a spectator ion. spectator ions are ions that do not participate in the reaction and are literally "spectators". if you notice in the question, you'll see that the change is changing on the NH3+ and NH2, and those are the only ions t...

lilymayek_1E

in terms of the equations representing galvanic cells, we'd flip the anode because all of the standard cell equations are in the form of reduction, which is the process that is occurring at the cathode. We'd flip the anode in a chemical equation because doing so, we'd represent the reaction occurrin...

lilymayek_1E

he finds the net production of gas because there are 3 mols of gas on the right side (products), 2 mols of gas on the left (reactants). Because this is a standard 1.00 mole reaction of O2, meaning the equation presented is what is occurring, you find the total production with a 3-2=1 mole of gas. th...

lilymayek_1E

thank you everyone! this helped much including lavelle's email. I think lecture notes, discussion notes, and textbook are the way to go.

lilymayek_1E

Can anyone guide me through part D of question 2 on the 'endgame' review? I've correctly calculated part B (which is to find deltaGo, Eo, and K) I'm quite sure, but every time I go through part D I feel like I'm getting a crazy answer. The galvanic cell is at 25C: Fe(s) | Fe2+(aq) || Ce4+(aq), Ce3+(...

lilymayek_1E

I'm not sure if this question has been answered yet on Chem Community, but what are the resources we'd use in this "open book" final scenario? Would it be our textbook and/or notes and/or chem community? That's what I've been assuming but is it stricter or looser than that?

lilymayek_1E

Ecell[o] is the standard cell potential; basically the calculated cell potential in standard conditions, which you find using standard reduction potentials. Ecell is the cell potential outside of these standard conditions, which you can use Ecell[o] to find this nonstandard potential.

lilymayek_1E

When you are solving for a redox reaction, and you split the original reaction into its respective half-reactions, you have to balance both the molecules involved and the electrons transferred. That final balanced value of electrons transferred is your n value. The top answer in this forum helps! ht...

lilymayek_1E

n indicates the number of electrons that are involved in the transfer between the oxidizing agent and reducing agent. When you have your two half-reactions for OX and RED, you have to balance your electrons to make sure your electron transfer is balanced out. The balanced value of electrons is what ...

lilymayek_1E

So in cases where kinetics dictate reaction rates, it is typically when there's a large energy barrier between the reactants and products & the reaction wouldn't happen in regular conditions & is typically irreversible. the example Lavelle gave was the reaction from Carbon (diamond) to Carbo...

lilymayek_1E

it probably won't count against you as long as you keep track of which K you're working with, e.t.c; I think in terms of concentration, I think Kc you can remember as c=concentration, Kp as p=pressure (equilibirum). it shouldn't be too big of an issue!

lilymayek_1E

the straight-line plot essentially means that as the reaction proceeds, the natural log of the reactant declines at the rate constant of k and is in first-order, and doesn't accelerate or decline across a particular time span.

lilymayek_1E

it's more to keep track of whether or not you definitively have a positive voltage value, but it's always a good idea to put + or - in front of your values because those voltage values (whether positive or negative) must be defined.

lilymayek_1E

so in general, I think it's a really good idea to always think of it in anode/cathode terms over left/right terms, just in case a question switches it on you. In this case, they actually do flip the cell diagram so you have to be a tad careful. so the standard reduction potential of Cu2+/Cu is +.34V...

lilymayek_1E

the n values in a balanced set of half-reactions don't change, but if the set of reactions happened twice for example, then yes technically the number of electrons transferred would change (but not fundamentally within the half-reactions themselves). you're right though with cell potential being int...

lilymayek_1E

the rate constant (which is k) should always be positive; you can think of a rate as always positive because k (a proportion between concentrations) is positive, and rate can be presented as K[R]^n, which must be positive as negative concentration or proportions cannot exist. on a graph of a first-o...

lilymayek_1E

you change the sign only on the anode because the anode is losing electrons (is the oxidation 1/2 reaction). every cell potential is given in reduction form, so you'll need to switch the sign to account for the oxidation 1/2 reaction.

lilymayek_1E

week 9, starts on Tuesday! that's what lavelle posted at the end of lecture :)

lilymayek_1E

oxidation is the process in which an atom loses an electron (LEO = Lose Electron Oxidation). an example of a redox reaction is Cu2+ + Zn -> Cu + Zn2+. A plus following an atom indicates that the respective atom has less negative charge (electrons) than it would in its standard form on the periodic t...

lilymayek_1E

the method to use without changing the signs is subtracting the anode cell potential from the cathode cell potential (subtract "Left" from "Right"). In the example of a Cu/Zn battery, the potential for the Copper reduction is .34V, and the Zinc reduction is -.76. You subtract -.7...

lilymayek_1E

platinum is used when there are no conducting solids, and Iodine in a solid form isn't a conductor; if you look on a periodic table, Iodine is one of the noble gases, which are all nonmetals (& on the nonmetal "side" of the table) and generally unreactive. they can't conduct electricit...

lilymayek_1E

an electrode is an electrical conductor that carries a current to and from non-metallic materials (solids, liquids, gas, e.t.c). in the example of an electrochemical cell (the diagrams Lavelle shows in his lectures), the electrode is that conductor that is inside the ionized liquid/gas to transfer e...

lilymayek_1E

when you use Van't Hoff, it's assumed that you're using it with a system that's under constant pressure, because the equation is in part derived from the Gibbs-Helmholtz equation, where pressure is assumed to be constant.

lilymayek_1E

to figure out oxidation numbers, there are different rules that help you figure out oxidation numbers. for example, any substance that contains atoms of only one element all have an oxidation number of zero, and H in any compound with a nonmental has an oxidation number of 1+. this article https://c...

lilymayek_1E

entropy is tied to the 2nd law of thermodynamics (which is that the entropy in a closed system never decreases; either remains constant in equilibrium or increases), and as far as I've looked electrons are so small in conjunction with the 2nd law, as well as somewhat having 0 entropy because of thei...

lilymayek_1E

I think it's always nice to remember those "essential" ones, like how free elements always have 0, oxygen is typically 2- in compounds, hydrogen is 1+, or ox number typically equals charge of a monoatomic ion. There's ~5 more I believe, so I think having the idea behind those wouldn't be b...

lilymayek_1E

heat capacity is a state function, because it doesn't matter how you added/lost heat or manipulated the temperature, it only matters what material the heat capacity reflects and the heat capacity in that particular moment, ignoring the pathways to get there.

lilymayek_1E

you can use qv and qp to denote which constant the system is in, but they also serve an important purpose because depending on whether a system is in a constant volume or pressure state changes the capacity to do work regardless of having the same internal energy. For example, because deltaU = q+w, ...

lilymayek_1E

state functions can be considered both extensive and intensive; a good example are heat capacity values. regular heat capacity, for example, is an extensive property because it depends on the mass amount in that particular moment. specific heat capacity(and molar heat capacity), on the other hand, i...

lilymayek_1E

I can send you them if needed!

lilymayek_1E

I don't remember having written down a specific equation, but combustion problems should probably ask for expansion/work of the gaseous products, and if you know the chemical equation as well as the starting number of moles for one of the reactants, you can. An example of this is the reaction C6H6(s...

lilymayek_1E

heat remains constant during a phase change because heat is being supplied to the phase change mechanism itself, not to the actual heating of the subject being heated. heat is being used in creating the phase change at the same rate that it's being applied to the actual material, so the heat remains...

lilymayek_1E

a regular calorimeter is insulated similarily to a bomb calorimeter, it's simply less sophisticated. a bomb calorimeter is completely isolated from the environment around it, while a regular calorimeter allows the contents to adjust to the external pressure, so it is not completely isolated to the e...

lilymayek_1E

qp=enthalpy change when there is no change in pressure; for example if the reaction occurred in a system where pressure was constant(an open beaker).

lilymayek_1E

heat capacity is, by definition, the heat required to raise the temperature of an object by 1 degree C. heat capacity by itself is an extensive property, which essentially means that heat capacity depends on the mass amount. specific heat capacity is an intensive property, which doesn't depend on th...

lilymayek_1E

I think you primarily have to understand that integrals basically represent the change in value over time (ex. the change in volume used in the work equation, e.t.c), and because we calculate that, we're essentially using integrals. I don't think we'll have to use it/explain it in terms any more com...

lilymayek_1E

using bond enthalpies to find overall enthalpy gains/losses is considered the least accurate because save for diatomic molecules, all other compounds are from averages across different molecules

lilymayek_1E

heat is a property that is heavily influenced by that path taken to reach its final value, which is what a state function is not. because heat is typically defined as the energy transferred between a system and its surroundings, the amount of heat transferred depends on the process happening in that...

lilymayek_1E

so conceptually, standard (reaction) enthalpy (which is what I think you're asking about) is the enthalpy when reactants are in their standard (most stable) state and the reactants are in their standard state as well. additionally, these standard enthalpies are all measured at 1atm, because at diffe...

lilymayek_1E

chem community questions are always due on sunday (11:59pm) I'm almost positive; that was the due date last quarter & I always posted before then and got full credit!

lilymayek_1E

work is defined as achieving some sort of motion against an opposing force, and is characterized by the equation w= opposing force(on object/system) x distance moved. you can think of it as lifting an object up off the ground; you're opposing the force of gravity by lifting that object, and moving i...

lilymayek_1E

state functions are only determined by final & initial values, much like how a state property is determined by its current state & not the path taken to obtain that state.

lilymayek_1E

the lecture last Friday was primarily focused on a lot of math concepts surrounding % pronation, pHs of salt solutions, buffers, and weak base/acid calculations. there were a lot of examples for calculations surrounding this, so I can send you an email with those examples!

lilymayek_1E

so I did this problem & checked the solutions manual, and really the only way it works well to get the final concentrations is to use the quadratic formula. Because every compound has an initial value (& will, as a result, have an "x" value of product added/removed), your K= P/R ra...

lilymayek_1E

you can use an ICE table for a buffer solution; we had the example of HNO2+H2O = H3O+ + NO2- in lecture to find the pH of that particular buffer solution; we can probably easily use the Henderson-Hasselbach equation too (as long as you don't get the acid/base & it's conjugate flipped around!)

lilymayek_1E

if you're talking about the "conjugate seesaw" example in lecture, you're correct in that [H3O+] is related to Ka (because it's the K constant of the acid). Ka and Kb are related to pH and pOH, because taking the negative log of that particular K value value (where it's the Ka or Kb depend...

lilymayek_1E

have we gone over this in class in an example equation? not really; lavelle primarily showed us pv=nrt and how we can get the calculation for concentration (concentration=p/rt) from the equation. there are a lot of practice problems in the textbook that are about going from partial pressure (p) and...

lilymayek_1E

electrons have properties that can identify them as both particles and waves. a good example of electrons being presented as particles is the photoelectric effect, where one photon at a particular level of energy can eject one (and only one) electron from a metal surface. Because one photon removes ...

lilymayek_1E

K is a summary of the composition of a reactant mixture at equilibrium essentially; it's a value that represents where reactants and products have no net change during the reaction, and this state is represented by K (which is essentially a ratio value between reactants and products).

lilymayek_1E

Q is representative of a chemical system's direction towards products/reactants at any given moment; so it can represent a system out of equilibrium or possibly a system in equilibrium at a very specific moment. Q can equal K in a given moment in time during a chemical reaction; it simply means that...

lilymayek_1E

K and Q values are found in mol/L most often, so you should convert those values from mmol to mol to get standard concentration values .

lilymayek_1E

oxalate is only a bidentate ligand because once two oxygens bind to a metal, their position is essentially fixed there. The two other oxygen atoms on the opposing side can't cross over to bind to the metal because it's impossible due to the existing bonds.

lilymayek_1E

it's not possible for CO3 2- to be bidentate to ONE metal (120 degree bond angle isn't big enough basically). However, if there's another metal present, another oxygen in CO3 2- can bind to that other metal, which will make carbonate bidentate.

lilymayek_1E

first, you'll have to use stoich to get the 13.6 mg of NaOH to moles (Because NaOH dissolves at 100% disassociation, you don't have to worry about any partial dissolving etc). once you have converted your NaOH to moles, you divide that value of moles by the number of liters. there's a 1:1 ratio of O...

lilymayek_1E

it's because cisplatin is more effective in binding to guanine to prevent DNA replication as opposed to transplatin. cis- and trans- determine the configuration of ligands around the platinum metal; cis means that two of the same atoms/molecules are on the same side of a molecule as the other, trans...

lilymayek_1E

in the textbook, there's a box in chapter 6 (6E.1) which does a really good job in explaining the different acids involved in acid rain. it proposes the automobile solution of reducing NO to harmless N2 to prevent it from forming nitric acid but doesn't go too into a deep explanation of chemical sol...

lilymayek_1E

in new naming conventions, both are cyanido. however, the old conventions (which I would use, personally) designate it as cyano (CN-, bonding on C) and isocyano (NC-, bonding on N)

lilymayek_1E

HClO4 is the stronger acid. The comparison here is that you have to look at electronegativities, a quality that Cl is stronger in than P. Cl is more electronegative, which means it draws electrons closer to itself and delocalizes electrons. This pull pulls electrons from H, making it unfavorable for...

lilymayek_1E

ferrate and cuprate are used when the coordination complex is negative overall. all of the metals can have -ate added to the end of their names, but iron and copper need to be in their latin terms (an easy way to remember is that iron = Fe & copper = Cu. FErrate and CUprate).

lilymayek_1E

you only write out the coefficient (the 2 in 2sp3) when involved in a bond where the quantum number involved in the bond is needed. lone pairs don't need the coefficient because they aren't involved in a bond where the quantum number needs to be specified.

lilymayek_1E

polydentate ligands are ligands that bind to a central metal atom with more than one atom (more than 1 binding site, or more than 1 e- pair donated). EDTA is an example of this - a hexa(6)dentate ligand with six donor atoms, all with e- pairs that can bind to a central metal atom or ion.

lilymayek_1E

because strong acids almost completely disassociate (overall, a higher number of protons are produced because a higher proportion of acid molecules disassociate). weak acids incompletely ionize, with a lower proportion of the acid ionized, which results in a lower number of protons produced.

lilymayek_1E

because strong acids almost completely disassociate (overall, a higher number of protons are produced because a higher proportion of acid molecules disassociate). weak acids incompletely ionize, with a lower proportion of the acid ionized, which results in a lower number of protons produced.

lilymayek_1E

this is true; for weak acids/bases we'd need to use the equilibrium constant equation which Lavelle said we wouldn't be using until 14B

lilymayek_1E

it's because bases reacts with oils & fatty acids on your skin (basically dissolves them), which removes friction, leading to that soapy feeling.

lilymayek_1E

it has to do with the formal charge of both; sulfur in H2SO4 has a charge of +2, while phosphorus has a +1 charge. Sulfur has a higher charge, so it'll withdraw e- density more from the surrounding oxygens than phosphorus. (e- density decreases so more H atoms in H2SO4 will disassociate). hope that ...

lilymayek_1E

the TM cation comes after the ligand names, and if there are any anions with a hydrate, anions follow the TM cation.

lilymayek_1E

9C.1 is called coordination complexes, and 9C.2 is called the shapes of complexes, hope this helps!

lilymayek_1E

you're typically don't use dashes I believe - when you write out a coordination compound all of the naming components come one after another (ex. the example from class. - [CO(NH3)5Cl]Cl*2H2O = pentaaminechlorocolbalt(II) chloridedihydrate)

lilymayek_1E

that's what I'm planning to do, just putting a little header before week 9 hw and a different one before week 10. probably be easier for TAs too?

lilymayek_1E

hybridization is favored when we have bond formation because the overall energy of two combined orbitals from hybridization is lower than if there were two separate orbitals in bond formation. lower energy indicates more stability, so hybridization is more favored. hope this helps!

lilymayek_1E

sigma and pi bonds are fairly easy to understand; the names are more used for identification more than anything else. sigma bonds are the first bonds that form between two atoms (that first line when you draw between two atoms in a diagram). pi bonds are any more bonds after that (double bond, tripl...

lilymayek_1E

a lot of how a molecule is polar or not can be determined by the symmetry of the molecule. if a dipole is present in an individual bond but has an identical counterpart opposite to that bond, the dipoles will cancel and the molecule will be nonpolar. if dipoles do not cancel due to symmetry, the mol...

lilymayek_1E

He didn't talk about T-shaped structures, but the VSEPR equation for T-shaped structures is AX3E2; 5 areas of e-density total, 3 bonded regions, 2 lone pairs (around central atom). The 2 lone pairs are in opposition to each other and push the 3 bonded atoms into a T-shape I found a good slideshow th...

lilymayek_1E

dipole-dipole refers to the interaction between two molecules that both have dipole moments; that is, both molecules/bonds are polar. dipole-induced dipole is the weaker interaction between a polar molecule and a nonpolar one; the dipole in the polar disturbs the e- field of the nonpolar structure e...

lilymayek_1E

Polarity in individual bonds is most often determined by the difference in electronegativity between two atoms; typically a difference of 0.5-1.7 between two atoms determines a polar bond. this is the more quantitative way to determine polarity in one bond. you can also look at the periodic table an...

lilymayek_1E

formal charge indicates stability (0 is best unless there is a distinct negative/positive charge on the molecule) but I don't think there's a particular way we need to know to find the contribution of each resonance structure? just understand that all structures contribute to an overall average (whi...

lilymayek_1E

possibly? the addition of pi bonds in a molecule does lead to increased electron density/orbital overlap, which impacts bond length and angles, which can impact geometry. mostly I think we'll have to see, but maybe know that bond number does impact strength and thus angle. hope this helps!

lilymayek_1E

when writing out the lewis structure, the order of molecules in this structure doesn't really matter (as long as carbon is central). The reason why the H's and Cl's are with their respective twin in a lot of diagrams rather than across has to do with dipoles and electric charge on each individual at...

lilymayek_1E

Isn't there a greater shielding effect because iodine has a larger atomic radius than the other molecules? Im having trouble conceptualizing this becuase I would think F2 would have a stronger interaction because fluorine is the most electronegative atom and I thought they want the electrons the mo...

lilymayek_1E

typically the indication on a three-atom molecule is the electron pairs around a central atom. When you draw out the lewis structure and determine whether or not the central atom has lone pairs determines angularity. If there are no lone pairs on the central atom, this typically means the molecule h...

lilymayek_1E

nodes are where the probability to find an electron in that orbital are zero. the number of nodes increases with quantum orbital number. for example, in a 2s orbital, there's one radial node, in a 3s orbital, there are two radial nodes. there important in terms of drawing the orbitals, but it's prob...

lilymayek_1E

formal charge is basically a way to keep track of electrons, and determine which lewis structure you draw is more stable for that respective molecule (especially if there's resonance)

lilymayek_1E

both sigma and pi bonds are from the overlap of orbitals - sigma is end-to-end (of two atoms), pi to orbital to orbital (of different atoms). a sigma bond is your first "basic" covalent bond - basically, the first line that you draw between two atoms is a sigma bond. Any more bonds added a...

lilymayek_1E

the more polarizability a bond has, the covalent the bond (basically the less ionic) it is. a good example of this is H2O; water is a polar molecule because the tendency of the anion (Oxygen) to be polarized by the cation (Hydrogen) is high; Hydrogen is able to distort Oxygen's outer electron hold e...

lilymayek_1E

A relates to the inverse bond order-bond length, and B is related to the size of an atom and the how bond length increases/decreases as related, hope this helps!

lilymayek_1E

since lavelle only introduced P, S, and Cl as the *current* exceptions we have to know, i'd say memorize those. But the general explanation for this is that Period 3(and greater) atoms have d-orbitals in their valence shells, which means that they can accommodate more electrons. (ex., Sulfer has the...

lilymayek_1E

Why is there more energy the farther an atom is from a nucleus? I'm going to assume you mean electron, but as an electron is further away from the nucleus, it's n value (representing energy and size of the shell) increases. additionally, an electron farther away from the nucleus is said to have hig...

lilymayek_1E

if you're asking about the value of L, L really only gives the shape of a subshell (s, p,d...). It's a label of the different subshells to distinguish them but doesn't explicitly tell you how many orbitals in the whole atom. electrons are more clear because there can only be a particular amount of e...

lilymayek_1E

Will bond length be given to us on tests or are we supposed to know bond lengths/assume resonance? Do you just base your lewis structure on the lowest formal charge? we probably don't need to memorize bond lengths, but in terms of resonance, I think that's something that we should be able to show (...

lilymayek_1E

I didn’t understand why oxygen received a negative charge instead of silver. Can someone please explain this to me? This has to do with the formal charge, or gaining/losing electrons when forming bonds. this is found with the equation FC = V - (L+(S/2)). To find the formal charge of oxygen in this ...

lilymayek_1E

for erica, think of electron energy being completely separate from the electrostatic attraction; this is primarily because the quantum levels for an electron solely depend on the electron itself, not the forces acting on it.

lilymayek_1E

wavelength, as everyone said above ^ is in meters, but probably know picometers (10^-12) and nanometers (10^-9) conversions, since those are the most asked/common ways its asked for wavelength!

lilymayek_1E

the unit keV is a kiloelectron volt, where an electronvolt is the KE gained/lost by a single electron (which would correlate with the photons in the question). the electronvolt is the standard unit, so a kiloelectronvolt is equal to 1000 electronvolts. **an electron has energy equal to 1.6022x10^-19...

lilymayek_1E

Like Taryn said, we use it to find energy/photon, substitute it in the rydberg equation (the equation used to find frequency, energy,et.c. of light when electrons go up/down quantum levels) & c=v(wavelength. it's used a lot; besides c=v(wavelength) I think it's probably one of the most commonly ...

lilymayek_1E

Where the light strikes doesn't really matter, primarily because we're focusing on the energy of the photon itself. Intensity doesn't impact energy/photon, just number of photons. However, if the number of photons was needed to be found in a certain amount of energy, you can find that with the energ...

lilymayek_1E

there's really no limit on the levels, but we give electrons quantum levels to serve as a quantifiable measure. additionally, the quantum levels correlate with the type of electromagnetic radiation (visible, ultraviolet) that is present at those energy levels (Lavelle had a slide demonstrating this ...

lilymayek_1E

not completely sure what you're asking, but in terms of value, typically anything smaller than a 10^-15 m wavelength has no detectable wave-like properties. the key here is detectable because it's assumed that every object with momentum has wavelike properties (like a car). however, a car is so larg...

lilymayek_1E

(a) from v(wave)=c, it must be true that the speed of light (electromagnetic radiation) is constant. thus, it's impossible for speed to decline (b) this is also false because of v(wave)=c. Because c is a constant, frequency and wavelength must have an inverse relationship to maintain this constant. ...

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