CHEMISTRY COMMUNITY

IanWheeler3F

A reducing agent is the species that gives up electrons in order to reduce a different species, since the reducing agent is giving up electrons this implies it is being oxidized. Th opposite is true for oxidizing agents; an oxidizing agent takes electrons so that a different species can be oxidized,...

IanWheeler3F

I was confused by this too but the question states that all the reactions are first-order so you need the first-order integrated equation regardless, what the 2A does is make you need to multiply [B]final by two (since 2 A are needed to produce 1 B) and then subtract that amount of A from the initia...

IanWheeler3F

probably the best xkcd comic to date

IanWheeler3F

I believe all metals in their solid form are conductive, and I'm pretty sure mercury is conductive too as a liquid metal. The thing about platinum that makes it special is its inertness, otherwise zinc, copper, tin, etc will all work as conductors, as long as its solid it should be conductive. But t...

IanWheeler3F

I think generally rate laws are written for species that are all in the same phase, and then if one reactant is in excess (like water) it can be treated as a constant and not a variable. But I don't think there is any rule that says to ignore solids and liquids, you just need to know what is reactin...

IanWheeler3F

I used $C(t)=C_{o}e^{-kt}$ so the equation needs to be solved for t in 0.0296 = 0.0611(e^((-3.7x10^-5)(t))) and I got 326.458 minutes for t
Your equation looks right but you have 3x10^-5 in it and not 3.7x10^-5, even that small decimal has a huge effect on the answer

IanWheeler3F

So the final rate law has [OH-] in the denominator but that's an intermediate just like HClO, I guess it makes sense being in the denominator since increasing it will consume HClO which is needed in the slow step, but are there any other scenarios where we are allowed to have intermediates in the ra...

IanWheeler3F

How im studying for this final

IanWheeler3F

For this I guess it helps to look at the base version of the H-H equation, pOH = pKb + log(BH+/B) So if pOH < pKb then pOH - pKb is negative, so the equation becomes: -N = log(BH+/B), where -N is just some random negative number then if you get rid of the log by doing 10^ to both sides you get 10^-N...

IanWheeler3F

so the general equation for a half life for an order greater than one (n>1) is \frac{2^{n-1}-1}{(n-1)(k)(C_{o}^{n-1})} so if you divide some half life t2 with initial concentration C2 over another half life t1 with initial concentration C1 you can derive the equation n = \fra...

IanWheeler3F

The general equation for a half life for order n is t_{1/2} = \frac{2^{n-1}-1}{(n-1)kC_{o}^{n-1}} so if you divide some half life t2 with initial concentration C2 over another half life t1 with initial concentration C1 you get n = \frac{\ln t_{2}/t_{1}}{\ln C_{1}/C_{2}} + 1 and in this case ...

IanWheeler3F

I think poisoning is when something enters the site and gets stuck so the enzyme doesn't function anymore, and then denaturing is when the enzyme loses its physical structure to do its function, I quickly looked that up i'm sure there's a better/more specific answer

IanWheeler3F

I used the equation k_{2}/k_{1} = e^{-(E_{a1}-E_{a2})/RT} and k2/k1 is the answer but you have to be really careful about plugging the values in. The Ea values HAVE to be in joules so they both need to be multiplied by 1000, and then R = 8.314, and T is in Kelvins. Also be sure you plug in t...

IanWheeler3F

i'm not exactly sure either but I think it may depend on the Ea of each reaction. What i'm thinking is if kf < kr but Ea for the forward rxn is 100J/mol and the Ea for the reverse is 50J/mol, then that means the exothermic reverse reaction is more likely and the overall should be exothermic. I don't...

IanWheeler3F

I think catalysts help reactions (any order) become so fast that they act like zero-order reactions, without them the order is probably higher. This has to do with the fact that catalysts have special shapes that can make reactions more likely to happen, so the new rate is essentially only dependent...

IanWheeler3F

I think it might have to do with the fact that once you put the integrated rate law equations (ln[C] and 1/C) in terms of C, C(t) = A/e^kt and C(t) = A/(1+Akt), respectively, where A = C(0), then you see as time goes on the denominator increases which makes both equations follow a curve that kind of...

IanWheeler3F

I remember the same thing happening to me and it honestly makes so sense, I don't know if there's an error or anything, but I did get the order of B as 2 using a different path. I found the order of A to be 2 using exp 1 and 2, then I skipped B and found the order of C to be 2 using exp 3 and 4, THE...

IanWheeler3F

The units of k are tricky but here's a good method to figure them out: M/s = (x/y) * (M^n) What is means is the rate is always molarity per seconds, M/s is the rate R (x/y) is the units of k that will make that side equal to M/s And then M^n is the concentration of the reactants to the power of the ...

IanWheeler3F

After you know the order of each reactant individually by forcing everything else to be zero-order, you now have the orders of all the reactants and then you add all those up and that's the overall order. So if I have the reaction A + B + C --> D and I found out their respective orders are 1, 0, and...

IanWheeler3F

maybe you're using scientific notation wrong? or not including enough digits? My numbers were a bit different but I did the same thing and it was right.

IanWheeler3F

I don't think theres an ICE box equivalent but if you know the k value, temperature, all initial reactant concentrations, and the rate law, you could use calculus to graph what would happen, but you need prior knowledge as mentioned. Otherwise you have to experimentally determine the a rate law that...

IanWheeler3F

I know balancing redox in acid means you use H+ in the balancing process and H+ may appear in the overall reaction, and then basic is the opposite with using OH-, but what does that mean about the solution pH? If I balance in acid and H+ is a product, and then balance that in base and OH- becomes a ...

IanWheeler3F

What do you think the rate of people disappearing was, zero order? First order?

IanWheeler3F

So you know the first step, isolate the half reactions after writing out oxidation numbers. After that its just a mess but there is a lot you can do during the process to make sure you're on the right track. First, its very tempting to go right into adding water to balance oxygen in a half reaction ...

IanWheeler3F

I cannot remember him specifically describing the difference but I do believe he has mentioned that gases aDsorb onto platinum electrodes and metal catalysts to make the reaction happen faster. I think it might be one of those things that people assume everyone gets even though its kinda confusing, ...

IanWheeler3F

Redox and electrochem are my favorites by far, I love how there are two mini reactions working together and they can all be combined and matched together with their unique potentials

IanWheeler3F

I'm a little confused as to why increasing temperature changes the k of the forward reaction more than the reverse, I know it has to do with the Ea values but I can't quite wrap my head around it, can anyone explain it?

IanWheeler3F

I remember in high school we used graphite for the anode and cathode lol There's also a class of metals called "noble metals" which is kind of a play on the "noble gases" in the sense that these metals so not react very much compared to other elements, some examples include palla...

IanWheeler3F

I know i'm late w the redox meme but i hope you enjoy

IanWheeler3F

Yikes I got lost too, but what really helped me get it was following it step by step and writing down the equations on a sheet of paper to do the math myself to make my brain go through the process visually. What I discovered is the rate of the thing you want (like rate of formation of NO2) is depen...

IanWheeler3F

k is always a positive value since it is just a proportionality constant, for example you can say the rate is proportional to the square of concentration and then equate them by saying R = k*(C^2). But we only put the negative sign in front to denote that the reactants are being consumed and to rela...

IanWheeler3F

I remember doing a lot more electrolysis in ap chem, one huge suggestion is know the conversions between charge, time, and current. For electroplating this big conversion is really helpful: Current and Time <--> Quantity of charge <--> Moles of Electrons <--> Moles of substance oxidized/reduced <-->...

IanWheeler3F

I suppose you could, but only in theory. Dr. Lavelle mentioned it briefly but true third-order reactions are very uncommon. For a fourth-order reaction you would need, I think, four total molecules/atoms/ions interacting in the rate-determining step and that is very very unlikely. But that is only i...

IanWheeler3F

k is constant but much like most constants it is dependent upon temperature, so I guess if your reaction is particularly endo/exo-thermic it may be tricky measuring k

IanWheeler3F

An appropriate meme for the kinetics unit

IanWheeler3F

So this one is weird and I hate it but the only two reactions that work for this are: O2(g) + 4H+(aq) + 4e- --> 2H2O(l), Ered= +1.23 V O2(g) + 2H2O(l) + 4e- --> 4OH-(aq), Ered= +0.401 V So you have to swap the sides of the second once since its Ered is lower and is less likely to be reduced so it is...

IanWheeler3F

So I looked up all the different potentials for all the metals for part A and the pattern seems to be that they want the reduction potentials for the SAME change in electrons. So for A you need Cu+2 --> Cu, Zn+2 --> Zn, Cr+2 --> Cr, Fe+2 --> Fe, and after you rank these redox potentials from most ne...

IanWheeler3F

I was confused by that too but this site explains it pretty well: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/02%3A_Reaction_Rates/2.10%3A_Zero-Order_Reactions It basically says zero order...

IanWheeler3F

Going off what Akash said, there's another example of adding a metal catalyst, and adding it makes it so much more likely that a reaction happens that it can change the order of a reactant to be zero since changing reactant concentration will have no effect on how fast the reaction is happening sinc...

IanWheeler3F

I believe the equations are the same since entropy is a state function and the path to final entropy does not matter, so both of their final entropies are the same. But irreversible processes cannot go back to the initial entropy after the final entropy is met, but reversible (not real) ones can.

IanWheeler3F

so true

IanWheeler3F

so like the subscripts say, you need to know when volume is constant and when pressure is constant. Constant volume is usually in bomb calorimeters or other sealed containers or any situation where NO expansion work is done, so under these conditions the pressure is increasing/decreasing. And then c...

IanWheeler3F

I think its because specific heat capacity (C sub s) has the dimension of joules per grams degrees Celsius (J/(g*C)). This means for water it will take 4.184 Joules of energy to raise one gram of water by one degree Celsius, and that is ALWAYS true one gram of water at STP, whereas heat capacity (no...

IanWheeler3F

So I used the tabulated values and the formula deltaH rxn = sum(deltaH formation products) - sum(deltaH formation reactants) to get deltaH rxn for 2 C6H6 (L) + 15 O2 (g) -> 12 CO2 (g) + 6 H2O (g) and I got -6271kJ/mol, so -3135kJ/mol for one mole benzene. But then the textbook says the deltaH combus...

IanWheeler3F

For 4C.3b the equation for delta H at a constant volume is deltaH = deltaU + nRdeltaT, and the energy put into the system is 765J, and the answer for deltaH is 1275J but I don't get where all this extra energy is coming from if 765J is being introduced. Does this mean the system gets more energy as ...

IanWheeler3F

Yeah it can since (Ka)x(Kb) is always equal to Kw=1x10^-14. So since you know Ka you rearrange the equation to get Kb = (Kw)/(Ka)

IanWheeler3F

After setting up the ICE chart you get 0.11-x for the E (equilibrium concentration) of HA, or undissociated benzoic acid, since you start off with 0.11M benzoic acid and then it dissociates into H+ and A- (general anion) so you lose some of the initial 0.11M to create [H+] and [A-]. But we also know...

IanWheeler3F

It means that the first deprotonated species contributes so little hydrogen ion that it has a negligible effect on pH. In this case it means that after H2CO3 becomes H+ and HCO3-, technically HCO3- can dissociate into H+ and CO3-2, but that second Ka value (Ka2) is so small that the final [H+] when ...

IanWheeler3F

For 'a' the lactic acid adds a whole bunch of H+ and in the reaction the concentrations are always in the proportion of Kc (or Keq) so when you add H+ the HbO2- is used up and therefore decreases in concentration. And for 'b' you use similar reasoning, O2 is on the products side so adding a lot of O...

IanWheeler3F

I think it just means that the amount of hydrogen ion contributed by the first deprotonated species is so minimal it has a negligible effect on the pH, I did the first calculation and got 4.18 (4.22 without making x=0) both times. I think Ka2 is only useful in polyprotic titrations, otherwise it can...

IanWheeler3F

This is a polyprotic acid problem so you need to have the Ka1 and Ka2 values since one hydrogen will dissociate from H2SO4 (a strong acid so it happens completely) and then ANOTHER hydrogen will dissociate from whats left HSO4-, an anion. You dont have to set up an ICE chart for the first dissociati...

IanWheeler3F

If you think about statues made by the ancient Greeks and how long ago they were made you would think that they would be long gone because of the rain eroding them constantly. But they lasted so long because only very recently did CO2 levels spike and increase acidity and cause their destruction. Ac...

IanWheeler3F

yeah, since SO3 is attached to three oxygens and then gains an attachment to one of the oxygens in H2O2, so SO3 accepts electrons making it a lewis acid, and then H2O2 the lewis base.

IanWheeler3F

It means the Ka1 for H2SO4 is greater than one so the ratio between H+ and H2SO4 (at eq) is so large that the amount of H2SO4 is trivial. For normal polyprotic acids I cannot think of much importance since the following Ka values are so small the amount of H+ they contribute is also trivial. Polypro...

IanWheeler3F

I like to think about it in terms of electronegativity, fluorine is THE most electronegative atom. It is extremely hard to contain it in its diatomic form F2 without it reacting. You will notice that some of the only compounds of noble gases are with fluorine. That is all to say is that when fluorin...

IanWheeler3F

The three chlorides are "spectator" ions meaning they do not participate in the reaction so they are ignored. I remember learning this in Ap, so when metal cations are in water they always form a hydrated complex with a number of water molecules twice the value of their oxidation state. So...

IanWheeler3F

pKa literally means "potenz of the acid dissociation constant," potenz is "power" in German which is where the p comes from. It essentially asks for the opposite of value of the exponent of Ka. pKa is used for buffers and choosing indicators, and it can predict pH as well which i...

IanWheeler3F

I think he may just want us to realize not all acids are strong and not all have just one Ka value if they are polyprotic. I remember we had a longer list like that in high school but it was only used for reference during homework, and it also had Kb and pKb values. I honestly don't know why it is t...

IanWheeler3F

Acidic and basic solutions are important because they are really prone to electron transfer, meaning they are very reactive. For example, bleaching works because it is very reactive with dyes and ruins the structure that gives dyes their color. pH is important because living organisms take advantage...

IanWheeler3F

For weak bases and acids they exist in an equilibrium with an equilibrium constant Ka (acid dissociation constant). So only a certain amount of protons or hydroxide are dissociated out. This concentration determines the pH, the negative log of [H+] or [OH-]. pKa is the negative log of Ka which is al...

IanWheeler3F

So for these you need to figure out where the cations and anions "came from" since salts are produced as the result of acid-base reactions. For example, KBr is formed when KOH and HBr react forming H20 and KBr. Now, we look at what the strength of these two acids and bases are. KOH is a st...

IanWheeler3F

You have to first know which ones are strong acids and strong bases, these will be the highest and lowest pHs. Then, figure out which of those strong acids/bases gives off more H+ or OH-, Sr(OH)2 gives off 2 OH- so it is 'more' basic and has a higher pH. Then, figure out which are weak acids/bases a...

IanWheeler3F

The Ka values of strong acids and bases are so large that it can be assumed that there is no back and forth between which species are present, there are just protons and anions.

IanWheeler3F

amphoteric is when it can act as either an acid or base, regardless of strength of the acid or base

IanWheeler3F

Im pretty sure HSO4- is amphoteric, it has a Ka value and can give up protons as well as accept them. Also hydroxide (OH-) is amphoteric since it can accept a proton to become HOH (H20) or give one up to become oxide (02-). There is also the difference between amphoteric and amphiprotic, amphoteric ...

IanWheeler3F

Water forms hydrates with a lot of compounds meaning it is acting as a lewis base and donating an electron pair. A well-known hydrate is epsom salts, which is magnesium sulfate. Water also forms complexes with other metals like sodium ions and aluminum ions when water dissolves them. I don't know ex...

IanWheeler3F

Ligands do not have to bond only with transition metals, aqueous sodium ions (and other metal ions) form hydrated complexes with water.

IanWheeler3F

Polydentate are usually organic structures with ammine groups, which in english is a big carbon- net with a bunch of nitrogen groups, and the nitrogen groups are the ones that bond to the metal. They are usually abbreviated so if you see en, pn, dien, trien, EDTA then these are all polydentate. Then...

IanWheeler3F

I think putting oxalato before aquo is part of an old naming system. I found this old chem textbook whose directions for naming coordination compounds says the ligands on the name go "negative, neutral, positive" which is consistent with putting a negative (oxalate) before a neutral (water...

IanWheeler3F

An example is [Pt(en)2Cl2]Br2 whose name is: Dichlorobis(ethylenediamine)platinum(IV)
Another is the ion [Co(en)2(H20)2] 2+ with the name: Bis(ethylenediamine)diaquocobalt(II)

IanWheeler3F

Like someone said about not needing to know this yet but, there are only 7 strong acids that dissolve completely into H+ and anions, and then there are only a few strong bases which are hydroxides of all group one elements and Calcium, Strontium, and Barium. Otherwise any other acid or base only par...

IanWheeler3F

They didn't explain it well in the textbook but I was always taught hydrogen bonds are between: 1. A partially positively charged hydrogen that is covalently bonded to a F, O, or N (because hydrogen bonding is "Fon") 2. A lone pair on any F, O, or N This means that water (hydrogen attached...

IanWheeler3F

We can look at electronegativities to see which atom has a higher electron density, and then you can draw dipole arrows which kinda look like this: +--->
the plus end is positive and the arrow end is negative, it will have a higher electron density

IanWheeler3F

If you're looking at a lewis structure or organic shorthand you can also look at the dashes and bars for bonds to see "shape" of a molecule, since dashes denote a bond going "behind" the paper and bars denote bonds poking "out" of the page.

IanWheeler3F

The axial atoms are in the most favorable positions because of repulsion and keeping the atoms the furthest apart they can possibly be, and then the two equatorial atoms must be in a bent shape since the electron pair repels them. In this shape all the atoms are the spread the furthest away from eac...

IanWheeler3F

Like everyone is saying, the difference between the two is how electrons are shared, ionic completely moves the electron but dipoles unequally share them. But the way I like to think about unequal electron sharing in dipoles is the resonance structure. The bond in HF is a single bond where hydrogen ...

IanWheeler3F

I think what it means is dipoles are only temporary and can merge to become neutral, so in the case of two dipoles when they are separated from each other the two dipoles stop reciprocating charge with one another. But a point charge (like an ion) is ALWAYS a point charge no matter how far away it i...

IanWheeler3F

I know we haven't discussed structure yet but AsF5 has no net dipole whereas AsF3 does have a net dipole moment meaning it has partially charged ends. So AsF3 will act like a little magnet and be more difficult to separate leading to it needing more energy to break the dipole-dipole IMFs so it will ...

IanWheeler3F

We usually say induced-dipole induced-dipole because the properties of hydrocarbons change very quickly as the number of carbons in a hydrocarbon increases. So like for methane there is only one carbon and four hydrogens meaning there are very few electrons leading to a very low attraction due to in...

IanWheeler3F

One way you can "know" there is a coordinate covalent bond is when you see these brackets [ ] and a metal and a bunch of molecules/atoms all stuck together in a chemical formula. Like here's a random one: [Pt(NH3)3(Cl3)]Cl. I know the question was for lewis structures so when you see these...

IanWheeler3F

This is a hard one but I guess it comes down to how far apart the charges are being distributed, like if there was a single bond between the 0 and -2 in one but a triple between the -1 and -1 then the charges on the -1 -1 are not only closer to zero but they are closer together, and it takes energy ...

IanWheeler3F

To be highly polarizable means that a molecule has so many electrons that sometimes a high density of electrons can be found on just one side of the atom. This high density all one one side creates a very temporary moment of unusually high negative charge, which means the other side without all thes...

IanWheeler3F

Also, and I know we don't talk a lot about d-block metals in this class, but when "identifying" delocalized electrons keep in mind that most of not all d-block metals do not keep the electrons in their outermost d-orbital very closely attached so they often move freely between themselves a...

IanWheeler3F

I don't know if an electron has a lot of energy per se, other than kinetic energy, do you mean it would take less energy to remove a delocalized electron? Because I would imagine if an electron isn't associated with any one atom then it would take less energy to remove since it is less tightly held,...

IanWheeler3F

Also you can find out which structure contributes the least by looking at experimental bond length. So if a molecule has three bonds and all three are determined to be the same at 155 picometers, but the single bond length would be 200pm and the double bond length would be 140pm, then you can probab...

IanWheeler3F

This also hold for chromium and coppers entire groups, 6 and 11 respectively. And yeah the d-block is weird since electrons are more stable when "symmetrical" with one another meaning a full or half full outermost d-sub level is most stable.

IanWheeler3F

I think its bc s-orbitals don't have nodal planes or weird orbital shapes that form around the nucleus like p, d, and f orbitals do. s-orbitals are an evenly distributed sphere that can get very close to the nucleus without touching it so since they're more likely to be closer to the nucleus they ca...

IanWheeler3F

For me I usually study in little bits rather than all at once or cram so I do one part of the textbook and its corresponding questions, and do a few sapling questions most days. And I also find videos online to be helpful if the textbook doesn't make sense

IanWheeler3F

the entire group 11 follows the same pattern, and then there's another weird group, 6, that fills half of its d orbitals after taking one electron from the outermost s orbital (for chromium its 3d5 4s1) since it is more stable to fill half of the d orbitals, much like how it is more stable to fill a...

IanWheeler3F

I think "effective nuclear charge" might mean the charges aren't balanced due to shielding and when charges aren't balanced one end of the atom has a different charge than the other leading the atom, despite its equal number of protons and electrons, to have charged ends

IanWheeler3F

what i understood was the energy given off going between any two n levels is E = -(hR)/(n^2) so as you change n levels near infinity you don't really change and distance and when you don't move you don't do work so the energy change is 0. Honestly I'm not 100% clear on it either since I don't fully ...

IanWheeler3F

The work function is like a threshold yeah, I don't know if theres a more "scientific" way to determine it but I got the impression it can be determined by doing the photoelectric experiment and using hv = p(Ke of electon) + (phi), and then solving for phi.

IanWheeler3F

the wavelength of the light is different because energy and frequency of light are directly proportional since E = hv, so when larger jumps are made in the Lyman series there is a larger energy change and therefore a higher of frequency of light is emitted, and UV light has a high frequency

IanWheeler3F

Everything everyone said I agree with just metals in the "d" block (the middle) of the periodic table all have similar properties notwithstanding the group they are in. That is to say they don't act as consistent in groups as group 1, 2, 17, 18 that all act incredibly similar within their ...

IanWheeler3F

if youre talking abt the model with the lines like n=1, n=2, etc then to read it you have to pay attention to the distance between the levels of n, its confusing but the distance between each level is not constant so the distance between n=1 and n=2 is much larger than the distance from n=3 to n=4, ...

IanWheeler3F

Also another thing about writing out molecular formulas from names is sometimes they'll say "cuprOUS oxide" or "cuprIC oxide" and the thing is a lot of metals have two really common oxidation states (charges) and putting -ous infers the metal has the lower charge whereas putting ...

IanWheeler3F

I think the bromine and magnesium are spectators? Like they don't play a meaningful part in the reaction and just end up as ions in solution and don't precipitate out (make a solid). And also this looks like an organic chem reaction so I don't think any of us understand exactly why it is the way it ...

IanWheeler3F

Just be sure to remember the metal has a +2 charge and you need 2 sulfides

IanWheeler3F

Adding on to the isotope comment, the reason carbon's amu is 12.011 and not 12 is because the 12.011amu is the average of the masses of all carbon isotopes, so while most carbon is 12amu, there is a smaller fraction of carbon in the universe that weights more (13amu and 14amu) so after dividing the ...

IanWheeler3F

To answer the part of your question pertaining to why it is hydrated is: a lot of (if not all) metals often form these "coordination complexes" where they bond with certain elements and molecules and ions (most notably water, ammonia, halides, etc.) and since water is extra "sticky&qu...

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