CHEMISTRY COMMUNITY

cassidysong 1K

Yeah I noticed the same error, I think it's just a mistake.

cassidysong 1K

It's Faraday's constant which will be given on the equation sheet.

cassidysong 1K

^^ Unique reaction rates means that it is the same for all reactants and products as opposed to the average reaction rate which can be different for each reactant and product.

cassidysong 1K

Yes, with higher temperature molecules move faster, therefore creating more kinetic energy.

cassidysong 1K

I know what A represents however I am confused by how you calculate A?

cassidysong 1K

How adding water affects cell potential is dependent on which solution it is diluting. If it is diluting the anode solution, then the overall Q is decreased, decreasing the lnQ expression and therefore increasing cell potential since the [-RTlnQ] term is smaller.

cassidysong 1K

^^^ I agree with Tyler, it depends on the reaction given. Through the reaction given you are able to determine which is the product and which is the recatant.

cassidysong 1K

If the cell potential is positive then it means the products are favored and therefore K>1 due to [producrs]/[reactants].

cassidysong 1K

For cell diagrams, theoretically I know that the reaction on the right is the cathode only if the cell potential is positive but for the purposes of the class, if the cell potential is not given then should one assume the cathode is the reaction on the right?

cassidysong 1K

How do you know which water reduction half reaction to use when looking up the cell potential?

cassidysong 1K

I am honestly not sure about the former but for the latter, the salt bridge is required so that the electrons continue moving throughout both solutions and keeping the voltage from reaching zero.

cassidysong 1K

Gibbs free energy is equal to the maximum non expansion work a reaction can do at constant pressure and temperature

cassidysong 1K

I believe he emphasized the log equation just because it is more relevant to life science but yeah I don't think it matters as long as you remember the conversion factor

cassidysong 1K

yeah I'm pretty sure the table of values will be given

cassidysong 1K

the higher the number, the stronger the agent

cassidysong 1K

^^ if Oxygen is in gas form, it's most stable, (O₂) then the charge is zero and if it is in a molecule with another element then it has a charge of 2

cassidysong 1K

the cathode is being reduced and the anode is being oxidized; that can be deciphered through the equations given

cassidysong 1K

the solids act as the electrode and is the thing that allows electron flow to happen from one cell to another

cassidysong 1K

to be more specific, when Q is less than 1 then the E of the cell is increased because it makes the ln(Q) term in E=E naught -ln(Q) and when Q is more than 1 then E of the cell is decreased

cassidysong 1K

in order to determine whether it is a reducing or oxidizing agent think about what the cell is doing to the other

cassidysong 1K

Because entropy is a state function you do not need to include the entropies along the way to the final state. The initial and final state are the same so the change is zero.

cassidysong 1K

When talking about that it's important to note what exactly the delta S is for. For reversible reactions the total delta S is zero whereas the delta S of the system is a number and the the delta S of the surroundings is equal and opposite to the delta S of the system.

cassidysong 1K

you usually only use it for phase changes because the temperature is constant

cassidysong 1K

^^ At constant pressure delta H equals q and at constant pressure work equals zero.

cassidysong 1K

When reading a problem how do you know which equation to use for ΔS?
options: ΔS= nRln(V2/V1) vs ΔS= Cln(T2/T1)
I'm having trouble distinguishing which to use based on the information given in problems, any insight will be helpful!

cassidysong 1K

Will we provided with the molecular structure of more complex molecules or are we expected to be able to deduce them? I am struggling to write the lewis structure for some of the more complex molecules (ex. CH3CH(OH)CH3 from 4E.7 b) and thus use the incorrect bond enthalpies; should I just practice ...

cassidysong 1K

Johnathan Smith 1D wrote:Would you happen to know what the answer is because I got an answer that I’m not sure is right?

During the review session I believe they said the answer was delta S =33.0 J/K

cassidysong 1K

entropy is actually an extensive property ( it depends on the mass)

cassidysong 1K

Yes, the Boltsmann Equation calculates positional entropy using degeneracy (W) and kB (Boltzmann's constant).

cassidysong 1K

The Joules can be converted to eV.

cassidysong 1K

Boltzmann's equation is used for positional/residual entropy which is present in everything but is relatively small.

cassidysong 1K

The three methods are Hess's Law, using bond enthalpies, and delta H = Σ delta Hf of products - Σ delta Hf of reactants.
Using the bond enthalpy method is the least accurate so if you can use other methods that's preferred.

cassidysong 1K

if it's a bomb calorimeter then it is an isolated system

cassidysong 1K

^^ what they said; if the system is doing work it's negative, if work is being done on the system then it's positive

cassidysong 1K

why do we need entropy in order to describe the system?

cassidysong 1K

I am confused on how Avogadro's number becomes involved in the W=2^N equation??

cassidysong 1K

yes aqueous solutions are included in eq calculations

cassidysong 1K

final exam pickup is in Young Hall 3034 from 9-5 (although they have an our lunch break at 12)

cassidysong 1K

There are different R constants that have different units so you just pick the R constant that has units matching the other parts (i.e. atm or bar)

cassidysong 1K

There is no need to calculate anything; just compare the two different K values.

cassidysong 1K

^^ bond enthalpy is always positive because by definition the energy is always being put in.

cassidysong 1K

An ICE table shows the change in concentrations the reactants and products go through from the beginning of the reaction to the end. I stands for initial, c stands for change, and e stands for equilibrium.

cassidysong 1K

^^as they stated K represents activity which is unitless

cassidysong 1K

reactants and products have an inversely proportional relationship, so if R goes down, P goes up, if P goes down, R goes up.

cassidysong 1K

^^ as the previous replies stated, expansion would affect Q (the reaction quotient) however it would not affect K because K is a fixed value.

cassidysong 1K

When volume changes it changes Q (the reaction quotient) however it does not change K because K is a constant of that molecule at that temperature. The only thing that can change K is temperature.

cassidysong 1K

the inert gas doesn't change the physical characteristics of the products and reactants

cassidysong 1K

Kw is the equilibrium constant.

cassidysong 1K

Yeah I don't think we've gotten to that part yet. Lavelle will probably go over it in class.

cassidysong 1K

Yes. Pressure isn't involved in Kc

cassidysong 1K

You have to find the equations in the table that could combine to create 2BrCl + H2 <--> Br2 + 2HCl and then use the K's to find the K of the overall equation. You can use the section 5H. 2 to decide what to do with the K's.

cassidysong 1K

cisplatin is [Pt(NH3)2Cl2] which is a chemotherapy drug. to be specific cisplatin has the Cl on the same side of the molecule so that the 2 Cl's bond with 2 Guanines on a DNA strand to shut down cell division.

cassidysong 1K

cassidysong 1K

if the overall charge of the coordination complex is not zero (i.e. a negative or positive number) then the end of the metal is changed to -ate. The only special names are iron which turns into ferrate and copper which changes to cupprate.

cassidysong 1K

if the overall charge of the coordination complex is not 0 (so positive or negative charge) then -ate is added to the end of the metal ion

cassidysong 1K

You'd simply add the charge of the ions together and then make it so that the charge of the metal ion plus the charge of the ions together equal -2.

cassidysong 1K

For EDTA the formula given by google is C10H16N2O8 but isn't ethylenediamine C2N2H8 so that would make each acetate C2H2O2 but isn't acetate C2H3O2?

cassidysong 1K

Its just to emphasize that it's the oxygen bonding to the compound.

cassidysong 1K

The charge of the metal ion is determined by counting up the charge of the other elements and then making the charge of the metal ion so that together it's equal to the total charge of the compound.

cassidysong 1K

Yeah unfortunately I think we just need to memorize the charges of the common ions

cassidysong 1K

The roman numeral tells you the charge of the metal ion.

cassidysong 1K

Yes if it has more than one lone pair (and thus can donate more than one pair of electrons) it is polydentate.

cassidysong 1K

In sigma bonds the areas of electron density are overlapping whereas pi bonds only have regions of electron density side by side.

cassidysong 1K

They mean the same thing, so either is fine

cassidysong 1K

In a coordinate covalent bond one atom provides both electrons.

cassidysong 1K

A coordinate covalent bond is when one atom shares both pairs of electrons.

cassidysong 1K

How is a trigonal bipyramidal shape nonpolar? How do the equatorial atoms' pull cancel out if they are angled in non-opposing directions?

cassidysong 1K

For part a of 2E. 25 how do you know that the chlorines are next to each other so that they don't cancel out? I know this is similar to the example Lavelle showed in class with the Dichloroethene, where cis was polar and trans was nonpolar but how do you know which lewis structure is the correct one?

cassidysong 1K

if the atom contains lone pairs it may affect the bond angles slightly because they have a stronger repelling force and push the other bonding electrons closer together, distorting the shape slightly.

cassidysong 1K

I don't believe it matters as it was referred to as angular in the textbook and Lavelle referred to the shape as bent.

cassidysong 1K

I would know it just in case

cassidysong 1K

lone pairs have a greater repelling force, therefore forcing the bonding electrons closer together and therefore decreasing the bond angle slightly

cassidysong 1K

^^^ lone pairs are always stronger than bonding atoms

cassidysong 1K

For the molecule ONF, how do you know which molecule should go in the middle? Generally the element with the lowest ionization energy is the central atom but doesn't oxygen have a lower ionization energy because it's more favorable to have 3 electrons in the 2d shell, so why is nitrogen the central ...

cassidysong 1K

I know that a resonant structure lowers the energy of a molecule to make it more stable but I don't really understand why having a mixture of structures help lowers the energy. Any insight would be helpful

cassidysong 1K

For reference for l,
l=0 ---> s orbital
l=1 ---> p orbital
l=2 ---> d orbital
l=3 ---> f orbital (we don't really need to know this)
the principal quantum number, n, just needs to be in the front so,
n=5 l=2 ---> 5d
n=1 l=0 ---> 1s
n=6 l=3 ---> 6f
n=2 l=1 ---> 2p

cassidysong 1K

ψ describes the system mathematically

cassidysong 1K

^^^ more electrons have more pull and make the bond shorter

cassidysong 1K

^^ atoms become more stable with bonds

cassidysong 1K

Yes, shorter bonds require more energy to break; double bonds and triple bonds are shorter than single bonds and therefore need more energy to break.

cassidysong 1K

In making a lewis dot structure you first think about the octet rule and then adjust the structure to have a better formal charge.

cassidysong 1K

What people above me said: it is better to be more stable if it is below period 3.

cassidysong 1K

Shared electrons are the electrons that are represented by the line in a lewis dot structure. Each line counts as 2 electrons.

cassidysong 1K

What the people of above me said :). The center atom's formal charge may not always be zero, if there is a choice between an outer atom with a formal charge of zero and the center atom with zero than it is best to have the center atom with zero.

cassidysong 1K

The goal is to minimize formal charge overall but if it comes down to minimizing the formal charge on one of the outer atoms at the expense of the center atom's formal charge increasing than it's better to have the center atom with the lowest possible formal charge.

cassidysong 1K

intensity depends on the amplitude of the wavelength and is directly related to the amount of photons while energy is related to if there is enough energy for the electron to be ejected.

cassidysong 1K

x, y, z, refers to the different planes that electrons are on

cassidysong 1K

^^ what they said. There's no technical rule but people usually just fill it in left to right.

cassidysong 1K

Hund's principle states that every orbital in a subshell will be occupied with one electron before any one orbital is doubly occupied. Whereas Aufbau's principle states that lower energy orbitals fill before higher energy orbitals so that orbitals in the n=1 energy level will fill before the n=2 ene...

cassidysong 1K

Thank you Dr. Lavelle for all of your instruction. Your passion for not only the subject of chemistry but the well-being of your students is palpable. Thank you for applying chemistry principles to a lab setting in order for us to understand the importance of every chemistry concept we learn.

cassidysong 1K

Yes it was derived from the photoelectric experiment.

cassidysong 1K

The De Broglie equation is to find the wavelength of matter since all moving objects with rest mass however it only has wavelike properties with an extremely small mass. The Rydberg equation is to calculate the amount of energy released when an electron drops to a lower energy level and works only f...

cassidysong 1K

When light intensity is increased, there are simply more photons and one photon interacts with a single electron. In order for each photon to have enough energy to eject one electron the wavelength needs to be shorter.

cassidysong 1K

Diffraction patterns are how light spreads out when it passes through a small passage. Based on the diffraction patterns there must be waves in phase (constructive) and waves out of phase (destructive interference) where the waves either line up with each other or they don't and they can cancel each...

cassidysong 1K

The Rydberg equation works only for the hydrogen spectrum because it was found based on the Hydrogen experiment. A more sophisticated model is needed for a multi-electron problem.

cassidysong 1K

No it doesn't matter.

cassidysong 1K

I'm pretty sure significant figures when adding or subtracting are dictated by the lowest amount of numbers after the decimal.
Ex. 12.5+5.35=17.9

cassidysong 1K

It's basically just a way to convert units from one to another. For example if you have distance given in yards (ex. 5 yards) you can use dimensional analysis to convert it into feet [i.e. (5 yards)x(3 feet/1 yard)= 15 feet; the yards cancel out and leave you with feet as the final unit].

cassidysong 1K

The general rule for the number of sig figs for an answer is exactly like what the previous reply said; they are based on the amount of numbers that aren't zero or any zeros that are in between other numbers. For example, 25.7 has three sig figs where as 25.07 has four sig figs. Another rule is that...

cassidysong 1K

If the given number is 25.92 mg of HF why is the amount of significant figures for the answer 3?

Search found 100 matches