CHEMISTRY COMMUNITY

Savannah Mance 4G

Can someone explain this problem and how the Le Chatlier's principle helps solve for what combination of HCl and NaOH would produce the largest change in temperature?

Savannah Mance 4G

Since we couldn't get Test 2 back my TA said they'd post the answer key to study from, but where did they post it? I don't see it on Lavelle's website.

Savannah Mance 4G

Why can you plug in the grams of the drug if you don't know what volume it is in? Since it's asking for concentration, how come you can plug in the 0.02 grams?

Savannah Mance 4G

For this problem, I'm confused on how to solve the rate equation with the given info. I know I'm supposed to use the equation with K=1/t*ln(A initial)/(A) but I don't get how the initial mass given is put into the equation to solve.

Savannah Mance 4G

Do we know that the order of the reactant C is zero because when experiment 1 is compared to experiment 4, the increase in reactants does not influence the rate?

Savannah Mance 4G

For this problem are we supposed to use the equation standard E cell= (RT/F) ln K? It says to look at the 6I.1 table but also this table doesn't show the K value for just a Nickel rxn.

Savannah Mance 4G

or is it the other way around?

Savannah Mance 4G

Is the element that is being reduced the one with a standard reduction that is the smallest or the most negative? and the one that is oxidized the one with the biggest or most positive standard reduction?

Savannah Mance 4G

For this equation when you solve for Q, the concentration of the H+ ion is found by doing 10^-pH which would be (10^-4) and then this is raised to the 16th power due to the stochiometric coefficient 16. But, this gives an answer of 1x10^-64 and then multiplied by conc. of the MnO4 and get 1x10^-68. ...

Savannah Mance 4G

Is the equation for Q from the cell diagram always going to be the anode over the electrode? Like for 6N.1 in the textbook with the rxn Mn(s)+Ti^2+---->Mn^2+ +Ti(s)? Or is it just like you'd normally do Q with products over reactants?

Savannah Mance 4G

For the single elements given, which standard reduction potentials should I use? Like for example one of the listed elements is Fe how should I know if I use the standard potential of Fe^3+ or Fe^2+???

Savannah Mance 4G

I'm so confused for like this whole problem because in the half rxns they include elements that aren't even in the entire redox rxn. Like, for part b the O2 included in the anode isn't in the whole redox rxn given. And for part a the Ag(s) wasn't in the full rxn either.

Savannah Mance 4G

So, from the cell diagram, the two elements don't have to be on opposite sides of the rxn? Like since O2 and H+ on the anode side of the cell diagram doesn't have to have a half rxn of O2--->H+?

Savannah Mance 4G

What is the cathode half-rxn for this ? I'm confused on what would make up this rxn.

Savannah Mance 4G

When you write the cell diagram do you always leave out stoichiometric coefficients? Also, how do you know when you need to add a platinum on the outsides?

Savannah Mance 4G

Can someone please explain the oxidation rxn with the anode for this one? I'm confused because the anode is O2 and H+ , how would this make up the anode rxn if it's not H20 to H+?

Savannah Mance 4G

Yeah, I'm pretty sure it's a typo and it's supposed to be Cl2 to Cl- not Cl2 to Cl2.

Savannah Mance 4G

The half rxn of Cl2--->Cl goes from a charge of 0 to a charge of -1 meaning the Cl is reduced. And in the other half rxn of Cl2--->HClO the chlorine is going from a 0 charge to a +1 charge and is oxidized. This is why it is both oxidized and reduced.

Savannah Mance 4G

Is the melting point temperature the same as the freezing point temperature because for problem 4I.7 part b they use the freezing point temperature as the melting point temperature. Is this specifically for C2H5OH or is it for all compounds?

Savannah Mance 4G

When finding the equilibrium temperature of water I don't understand why you wouldn't multiply the grams given by the specific heat capacity for the how water and the cold water? Why do they just cancel?

Savannah Mance 4G

Which phases of water are included and not included in the equilibrium constant? Is it included when it's a gas and solid but not liquid?

Savannah Mance 4G

Can someone please explain how to do this problem I don't know how to do it with all of the given values. I'm really lost because there is no Kc value given either.

Savannah Mance 4G

What is the difference between the two questions because they both ask for the Gibbs free energy of the rxn I2<-->2I but they have different answers. Can someone explain why they're different?

Savannah Mance 4G

For 4G.5, how is a cis molecule structurally supposed to be arranged? I know for the trans molecule it needs to have its X and Y molecules on opposite sides but I wasn't sure for cis.

Savannah Mance 4G

Lavelle said that Test 2 will include the 2nd page of Thermodynamics and all of Electrochemistry! :)

Savannah Mance 4G

The element or molecule that is being oxidized is the one that is losing electrons and whichever is being reduced is the one that is gaining electrons. My high school chem teacher taught us the acronym OIL RIG to help us remember (oxidation is loss of e- and reduction is gain of e-). Hope that helps...

Savannah Mance 4G

For this problem, why do I have to multiply the - change in enthalpy of fusion by the amount of moles? I thought enthalpy was a state function why does it have to be multiplied by the amount of moles of H20?

Savannah Mance 4G

I was a little confused about entropy because I thought that if the temperature was higher, there would be more disorder and entropy considering under conditions of high temp. the molecules would move around faster and be more "disordered". But, the entropy equation says otherwise since th...

Savannah Mance 4G

I know Lavelle said he's moving test 2 to week 9, but does that mean we're going to have it the same week as our final? Isn't that finals week?

Savannah Mance 4G

When your using the entropy equation with delta S= KblnW the units that W converts to is J/s but I was confused because if you use the Kb the units cancel to leave 1/K*s. Aren't the units for entropy supposed to be J/K?

Savannah Mance 4G

Can someone explain why it is false that removing heat from the system is exothermic and the temperature will decrease?

Savannah Mance 4G

Whenever you're asked for heat capacity are you suppose to always give an answer in J/g/Celsius ? Do you do this even if they give you a q that's in KJ?

Savannah Mance 4G

Is the enthalpy of formation of all diatomic molecules 0 ?

Savannah Mance 4G

Do we always assume the temperature is 298 K when we have to use the equation (change in enthalpy) = (change in internal energy) + (change in moles) RT? And if so why?

Savannah Mance 4G

For 4D.5 why is the change in enthalpy equal to the heat supplied if there was expansion work done? I thought there had to be no expansion for the change in enthalpy to equal q.

Savannah Mance 4G

In 4C.13 why do you add enthalpy to the heat supply of the ice??? I understand why the heat gained by the ice is equal to the heat lost by the water. But, I don't get why the change in enthalpy is being added to the head gained by the ice.

Savannah Mance 4G

When a question asks for final temperature how do you find that? What equation do you use? Do you use the enthalpy equations?

Savannah Mance 4G

In the equations that Lavelle did in class when he was showing different methods to find enthalpy he used kJ with Hess's Law.

Savannah Mance 4G

I'm kind of stressing out because I feel like I'm not going to be able to remember all these different equations and when to use them. Like the different equations for work and internal energy. How do you memorize all of them???

Savannah Mance 4G

When something goes from a solid to a liquid instead of liquid to solid in fusion, why is it still going go be a positive enthalpy value?

Savannah Mance 4G

When a question asks what is the change in the internal energy of a reaction, what are they asking you to find? Are they asking for the work?

Savannah Mance 4G

For the work formula for expansion it is - P x change of volume but for the other formula it has P x a x d. I was just wondering why the second equation doesn't have a negative sign in it.

Savannah Mance 4G

Is the Ka of a strong acid like HCL just 1 since it fully dissociates?

Savannah Mance 4G

Does anyone have some good Youtube video suggestions for someone who's super confused on weak acids and bases and salts?

Savannah Mance 4G

In 6E. for #1 the H2SO4 in its second protonation for the ICE table it's supposed to have a concentration of 0.15 for H3O+ the same as the H2SO4 initial concentration. But for #3 when H2CO3 is protonated, the H3O+ concentration is not 0.01 like the initial of H2CO3. I was wondering what made them di...

Savannah Mance 4G

How do you know whether a molecule is an acid or a base? I was doing the problems in 6D and I didn't know how to set up some of the equilibrium equations because I didn't know if they were acids or bases. Is there a way to tell?

Savannah Mance 4G

Is the test the Tuesday we get back from the weekend on Jan 21st? And is it just on Chemical Equilibria and Acid & Base Equilibria?

Savannah Mance 4G

On the problem 5.39 it tells me to refer to 5E.2 table but I looked in 5E chapter and there's only one table and it's 5E.1. Does anyone know where to find the table?

Savannah Mance 4G

Sorry I meant to say I got -2.92 for b in the quadratic formula

Savannah Mance 4G

In the homework 5I.27 for part c, for the quadratic I got -2.92 instead of -4.92 and I'm not sure why. Can anyone help?

Savannah Mance 4G

In the homework problem 5I.19 it asks for the equilibrium constant for the reaction of H2+I2<--->2HI if initially there is 0.4 mol of H2 and 1.6 mol of I2 in a 3.0 L container. They say that 60% of the hydrogen has reacted. When you are doing the ice table for the problem I thought that since the hy...

Savannah Mance 4G

How do you know when a question requires an ICE table? I know that an ICE table is only used when they don't give you the equilibrium initial concentration. But, will they tell you they're not the concentrations at equilibrium? How will the problem usually be worded for ones that require ICE tables?

Savannah Mance 4G

For 5I.13 I did the ice table correctly and got 0.0001-x for Cl2 and +2x for 2Cl. I did the quadratic to find x and got 5.6*10^-6 and then plugged it in to get 1.12*10^-5 for the 2Cl but it's not the right answer. I'm not sure what I'm doing wrong.

Savannah Mance 4G

In 5G.9 it says in two containers, one with 0.1 mol of O3 and the other with 0.5 mol of O3 with the rxn 2O3(g)<--->3O2(g) taking place will ratio of PO2/PO3 be the same (part b). I understand that the ratio won't be the same for the two containers because the partial pressures of the O3 as well as t...

Savannah Mance 4G

Does anyone know if we have to memorize certain K values? Like some of the homework problems don't give the K value and ask for you to refer to the table in 5G. Would we have to memorize that table?

Savannah Mance 4G

Okay, that makes a lot of sense!!!! Thank you :)

Savannah Mance 4G

The problem 5G.1 (d) asks if it's true or false that the gibs free energy is greater than the standard gibs free energy will proceed to equilibrium. Isn't this false because the gibs free energy must go to 0 to reach equilibrium rather than be bigger?

Savannah Mance 4G

For the homework problem 5H.3, it asks for the K value at 300 kelvin for the reaction 2BrCl(g) + H2(g) > Br2(g) + 2HCl(g) using the Table 5G.2. I wanted to combine H2+Cl2>2HCl which had a K of 4.0x10^31 at 300K and then Br2>2Br. But for the Br equation the kelvins listed were either 1000 or 1200. Is...

Savannah Mance 4G

If the atoms in a lewis structure have formal charges that add to zero is this more stable than having one atom with a formal charge of 0 and the other with a charge? Like say for (C2)-2. You could have a double bond and have a carbon with a 2+ charge and carbon with 0 or a triple bond and have a ch...

Savannah Mance 4G

Is the E in the AXE the lone pairs on the central atom or all of the atoms?

Savannah Mance 4G

how are pkA and kA related and how do they relate to how strong an acid is?

Savannah Mance 4G

Is it possible for a molecule with only two atoms to have resonance?

Savannah Mance 4G

I went to a late quantum review session and they showed this equation z effective which is supposed to represent the number of protons multiplied by e which is charge of proton and electrons. And then there was another equation with (z effective) x (e) = (z theoretical) - (electron electron repulsio...

Savannah Mance 4G

Why does the most stable structure for carbon monoxide have a triple bond between carbon and oxygen and 1 lone pair on each? I thought it would be a double bond between carbon and oxygen with one lone pair on carbon and one lone pair on oxygen because this gave me a formal charge of 0 on both carbon...

Savannah Mance 4G

A dipole induced dipole describes the forces between a polar molecule and a molecule with no charge. An example is HCL and Ar. Argon has no charge and HCL has a positive dipole on hydrogen and a negative dipole on chlorine. The Argon's electrons will be drawn to the positive charge on the hydrogen b...

Savannah Mance 4G

Can someone please explain to me why the electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s1 is copper and not potassium?

Savannah Mance 4G

I'm kind of confused as to when a molecule has hydrogen bonding. Like, is hydrogen bonding present whenever there is a hydrogen in the molecule?

Savannah Mance 4G

I know that we're given the equation for Heisenberg on the constant sheet but do we need to know how to use it?? Like if we know a problem has uncertainty according to the Heisenberg uncertainty principle do we just state how it applies and that's it? How would you answer the question?

Savannah Mance 4G

I know on the constant sheet they write the Rydberg formula as En=-hR/n^2 but the other way to write it is v=R(1/n1^2)(1/n2^2). When do you use one versus the other? Like what kind of problems would you have where you would need to use the other version?

Savannah Mance 4G

In the question where it asks to determine whether the change in energy will be positive or negative in the hydrogen atom that is excited by a photon with a wavelength of 102.557nm. . . I found the change in energy was 1.9x10^-18 and the E initial was -2.18x10^-18. For the E final I used the equatio...

Savannah Mance 4G

I'm trying to name K2 [Ni(CN)4] but I was confused because I know you're supposed to start the name with the prefix for how many ligands there are, so in this case tetra since there are 4 CN. Then, I thought I was supposed to do the TM cation name but I was confused because in the formula isn't the ...

Savannah Mance 4G

When a question asks for the VSEPR formula, is it asking for me to explain how the vsepr theory of electron repulsion relates to the molecule? What does it mean by formula?

Savannah Mance 4G

If the shape of a molecule is square planar with two lone pairs, what are the bond angles? Do the lone pairs affect the bond angle ? Would it have the bond angle of an octahedron since it has 6 areas of electron density?

Savannah Mance 4G

Are molecules that are trigonal planar usually non polar?

Savannah Mance 4G

On the midterm there was a question about the longest wavelength needed to remove an electron from gold. But, they only give the work function. I tried rearranging and combining formulas but I always end up with two unknown variables. How would I solve this problem? Does anyone know what combination...

Savannah Mance 4G

I wanted to study from previous exams given by Lavelle. I heard that I can find them at the test bank. Where is the test bank?

Savannah Mance 4G

I think I have the concepts down pretty well from lecture and I do all of the homework problems. But, when I take the tests I kind of blank and I think it's because I get kind of nervous. Does anyone have any advice for that?

Savannah Mance 4G

For the midterm, I used the dino nuggets practice review. Is there one similar to that for the final exam. Also, does anyone have tips on how to study besides the review sessions???

Savannah Mance 4G

I was doing homework problem 9C.9 where I'm supposed to find the coordination number. But, I didn't know what en or edta stood for in the compounds. Like one was [PtCl2(en)2] and the other [Cr(edta)]. What molecules are en and edta ?

Savannah Mance 4G

For tests are we supposed to memorize certain bond lengths or are they given to us in order to do the calculations?

Savannah Mance 4G

How do you draw lewis structures for complex organic compounds? Like for example CH2CHCN? Do you draw you connect all of the carbons first or do you like draw parts of the compound separately and then see where they can fit together? I'm pretty lost on how to draw it to be honest. Any help would be ...

Savannah Mance 4G

How do you know when the central atom will have lone pairs instead of more bonds?

Savannah Mance 4G

Why does arsenic have lone pairs? And how would you know it would have lone pairs being the central atom?

Savannah Mance 4G

How do you know when a compound is radical and which atom will have the unpaired electrons?

Savannah Mance 4G

I'm still pretty confused on when to do double and triple bonds on a Lewis structure. For example in the compound AsF3, I'm not sure if it's supposed to have a double bond on two of the fluorines. I calculated formal charge and with the double bonds on two fluorines, I get a formal charge of 0 on ar...

Savannah Mance 4G

Where do we check our midterm grade since it's not on CCLE? Sorry if this is an obvious question...

Savannah Mance 4G

For questions for chem in general, do you give the answer in the units that the question uses? I've been converting everything to the standard units (meters, liters, Kelvin, kilograms, seconds) regardless of what the equation gives. Am I supposed to keep the answer in the units that the question has...

Savannah Mance 4G

Can someone explain to me why s-electrons have a lower energy than p or d electrons. I knew that inner electrons shield the outer electrons from electrostatic attraction of the positive nucleus so I thought this meant they needed a higher energy to shield.

Savannah Mance 4G

In the photoelectric experiment when they doubled the intensity of light, electrons were still not ejected. What is intensity? Is the intensity the frequency or the wavelength?

Savannah Mance 4G

I've seen the equation for the energy of a photon joined with the debroglie equation but I never understood how. Can someone explain how they can be put together?

Savannah Mance 4G

I've seen the speed of light equation also be written with velocity in place of c. Are velocity and speed always used interchangeably or is it only for speed of light because light only travels in one direction?

Savannah Mance 4G

In the spectral line series, the series is describing how the hydrogen transitions from a higher energy level to a lower energy level and emits light. If the hydrogen atom is going from a high energy level to a lower energy level, then why is n1 the lower energy level? Wouldn't n2 be the lower one s...

Savannah Mance 4G

On the homework for problem 1B.15, the equation gives the velocity of the photon. I used the velocity to find the kinetic energy of the photon. However, the problem asks me to find the wavelength. But, there is no given work function or energy of the photon. How am I suppose to solve for the wavelen...

Savannah Mance 4G

In this problem, the given information is that a y-ray has energy of 140.11 keV and I'm supposed to find the wavelength. I know I'm supposed to use Einstein's equation. But, what is keV? What is this unit? I've never seen it before so I have no idea how to convert it or if I even have to.

Savannah Mance 4G

I know that a black body is an idealized object that absorbs all incoming light. But does it also hypothetically reflect light as well? And if so does it reflect light of all wavelengths?

Savannah Mance 4G

Or what is the difference between quanta and a photon?

Savannah Mance 4G

Just checking but in Planck's Law the electromagnetic energy is in the form of quanta and quanta is also a photon right? Quanta and photon can be used interchangeably? They are the same thing?

Savannah Mance 4G

When light goes from high energy to low energy does it emit light? And when it goes from low energy to high energy does it absorb light? Or is it the other way around?

Savannah Mance 4G

Dr. Lavelle mentioned Planack's constant is h=6.63x10^-34 J.s in lecture. What is Planack's constant used for or what is it a constant for?

Savannah Mance 4G

The textbook said that Avagadro's constant is not a pure number and can be given units (molecules, formula units, atoms, ions). Avagadro's constant can also be written as N with subscript A.

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