CHEMISTRY COMMUNITY

Riley Dean 2D

Angela Cong 3C wrote:Does a concentration cell always have to have a porous disk?

A concentration cell can have a salt bridge as well, its essentially the same as a porous disk but one of these is needed

Riley Dean 2D

Is there a case where Ecell could be negative?

Riley Dean 2D

Platinum is used in a cell diagram as an electrode when no other solids are present, it is added to either end of a cell diagram depending on where its needed

Riley Dean 2D

Delta G is positive in photosynthesis, photosynthesis requires light making it not spontaneous

Riley Dean 2D

You can use the equation to find the K value at two different temperatures

Riley Dean 2D

You can use this equation to find a lot of things depending on how you decide to rearrange the equation, but you know you need to use if the reaction involves a temperature change

Riley Dean 2D

More often than not the solid used is going to be platinum but you can also use graphite as a conducting solid

Riley Dean 2D

Technically nothing in the class is curved, the tests are given a score but not a grade and then at the end of the quarter once everyone’s scores out of the total 500 for the class is known is when a grade is given

Riley Dean 2D

It doesn’t always mean that entropy is lower, you could have different sign combinations for enthalpy and entropy causing the negative delta G

Riley Dean 2D

Since it’s in the homework I would assume so

Riley Dean 2D

They both have the same purpose so the question should tell you what’s used

Riley Dean 2D

705170809 wrote:Do you think he will also have enthalpy and entropy questions imbedded in Gibbs questions, since Gibbs free energy contains a formula that requires both delta H and delta S?

I’m not really sure but it wouldn’t hurt to know it just in case

Riley Dean 2D

Cp and Cv are different because Cp is used at constant pressure and Cv is used when volume is constant, they’re both calculated using R and some other number which should be given on the equations sheet

Riley Dean 2D

Can someone please explain the derivation of deltaS = nRlnV2/V1 ? I do not understand why this can be used. This equation is used in an isothermal reaction so temperature is constant which means that deltaU is 0, this allows q=-w, because w=-nRTln(v2/v1) then q=nRTln(v2/v1), then, since deltaS=q/T,...

Riley Dean 2D

Because the equation P1V1=P2V2 is true, you can manipulate it so P1/P2=V2/V1

Riley Dean 2D

Delta U is the change in internal energy and its a state function so its only dependent on the end state, its just the difference between where you start and end up in terms of energy

Riley Dean 2D

I think either works, the solutions manual for the seventh edition I’m pretty sure uses 273

Riley Dean 2D

R is used for reversible reactions when temp is constant, usually like if you have deltaS=nRln(v2/v2), then use deltaS=nCvln(t2/t1) for a constant volume and a change in temp and then deltaS=nCpln(t2/t1) for a constant pressure and a change in temp

Riley Dean 2D

Concentration is calculated by mol/L so if you change the volume it will cause a change in concentrations and therefore a shift in equilibrium, but if you dont change the volume and just pump in inert gas then the reaction will stay the same because none of the variables within the equation for conc...

Riley Dean 2D

When volume is decreased it is most likely that that will cause pressure to increase, therefore causing the reaction to shift to the side with fewer moles

Riley Dean 2D

In a closed system, energy can be exchanged with the surroundings but not matter, the example used in class was a beaker that had been sealed, in an isolated system does not allow for heat or energy to be exchanged with the surroundings, a helpful way for me to think of it is to think of it similar ...

Riley Dean 2D

Their value cannot be determined based solely on their current state, the path taken must be considered, whereas something like enthalpy can be determined on its current state

Riley Dean 2D

Heat does not have state properties because it is not a state function meaning that heat relies on the ‘path taken’ where as enthalpy does not and its value is determined by its current state

Riley Dean 2D

Yes, when calculating net enthalpy change, you will have to take into account enthalpy changes between states of matter

Riley Dean 2D

Don't round any answers until you've reached the end of your work, then round off to as many sig figs as the equation used

Riley Dean 2D

They are often used interchangeably because they are the same thing, although its more common to see ionization

Riley Dean 2D

Usually the equation will tell you whether if it wants partial pressure or concentrations, but if within the chemical equation there is an aqueous solution then it will most likely be asking for concentrations

Riley Dean 2D

If the pressure is increased by decreasing volume then that is correct but if pressure is increased by pumping gas in then that would be incorrect because moles and volume will have stayed constant and therefore the concentrations will have stayed constant and no change in the reaction will occur

Riley Dean 2D

You can also tell by looking at if the equation is made up of all gases or if its made up of aqueous solutions, gases meaning use Kp and aqueous solutions meaning use Kc

Riley Dean 2D

Bar and atm can be used interchangeably because they’re so close to equal in value

Riley Dean 2D

Bronsted focuses more on the transfer of protons and lewis focuses more on the transfer of pairs of electrons

Riley Dean 2D

Acidic rain occurs when sulfur dioxide and nitrogen oxide mix with water molecules and create acid, acid rain can be prevented by lowering emissions and using more renewable energy sources

Riley Dean 2D

if the pH is lower then the acid is stronger, I feel like its just something you kinda have to know

Riley Dean 2D

every bond after that first sigma bond is going to be a pi bond so there is one sigma bond and then two pi bonds in a triple bond

Riley Dean 2D

On a test will both notations be counted as correct?

Riley Dean 2D

Does it matter if we put the 2 in front of it on tests? or are both ways counted correct?

Riley Dean 2D

every bond begins with a sigma bond, then when you have a double bond you have a sigma bond and pi bond, the bonds after that first sigma bond are going to be pi bonds

Riley Dean 2D

All of these are 180 degrees right? regardless of the number of lone pairs of elections?

Riley Dean 2D

its probably best to be prepared, just in case it does come up on the test, and since it is in the homework I'm sure its expected that we know it

Riley Dean 2D

within a lewis structure if there is single and double bonds, then the bond length of all the bonds is going to going to be the same and it will be a length somewhere in between that of the length of the single bond and the length of the double bond, this is because this creates a more stable struct...

Riley Dean 2D

If it is a structure where you can change where the double bonds go while keeping the charges the same except for the molecules that you shifted the bond between, then draw the resonance structures and the double arrows between them because the most stable structure is a mixture of the resonance str...

Riley Dean 2D

also if the structure has some single bonds and some double bonds the overall bond length will be somewhere between the given values for two types of bonds

Riley Dean 2D

final grades are assigned at the end of the quarter once they figure out the class average, we kind of just have to wait to see what an A is

Riley Dean 2D

does anyone happen to know why it averages out so they're all the same length as opposed to just letting the double bond be a different strength than the single bond?

Riley Dean 2D

the stronger the bond the harder to break therefore resulting in a higher boiling point

Riley Dean 2D

Are we also supposed to have memorized the exceptions to the electronegativity trend? i.e C, N, O, F

Riley Dean 2D

we just need a pen, a simple scientific (non-graphing) calculator, and a photo ID

Riley Dean 2D

Which element of the following pairs has the higher electron affinity: a)tellurium or iodine, b)beryllium or magnesium, c)oxygen or sulfur, d)gallium or indium; i thought that as you moved across a period and up a group electron affinity increased, but the answer key says that suffer has higher elec...

Riley Dean 2D

how would one know that O>Cl?

Riley Dean 2D

if the element has 8 valence electrons then its a full octet, the main exceptions to the rule are hydrogen, helium, lithium and barium

Riley Dean 2D

im not quite positive but i think it has something to do with the fact that electron affinity is measuring the amount of energy released, therefore the change in energy is going to be negative

Riley Dean 2D

I'm pretty sure Lavelle said that only what was covered up until Friday's lecture is going to be on the test

Riley Dean 2D

The test will only cover what we've learned in the quantum world up until Friday's lecture

Riley Dean 2D

with this question, I know I'm supposed to use de Broglie equation which is wavelength=h/p, where p equals mass times velocity, i was just wondering how to find the mass of the electron so that i can find p

Riley Dean 2D

I think test 2 is going to be chapter one and some of chapter two but I'm not quite positive

Riley Dean 2D

I think it would just be helpful to be able to know kind of generally where different wavelengths fall within the spectrum and then know the order in which they fall, like knowing which types of light are bigger and smaller than what other types based on their wavelength

Riley Dean 2D

what exactly is meant by the extent of the change in the electrical field at a given point?

Riley Dean 2D

Does anyone know if/when the modules are due and if they're graded at all?

Riley Dean 2D

Can someone explain what the rule is for 120 to be only two significant figures while 120. is three

Riley Dean 2D

Does anyone know when the cutoff for week one's discussion period is? Like how long we have to post for week one and when week two starts?

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