CHEMISTRY COMMUNITY

abbydouglas1K

could someone please explain #8 part a on the electrochemistry worksheet? How do we know that S2O8 2- is reduced and NO is oxidized? I also have this question You look at the chart of reduction potentials. The one with the higher reduction potential will be reduced. For the other half reaction, it ...

abbydouglas1K

For worksheet 4, is the answer for 6a wrong? I did (3/2)(31.9 mol)(8.314 J/Kmol)(311.15 K) = 124 kJ. When I didn't convert the temperature from C to K I got 15.1 kJ which is the answer given in the key. We don’t have to convert it to kelvin as it is change in temperature (38-0) Why do we use that e...

abbydouglas1K

For the first law worksheet, how do you do #2? First you have to do stoichiometry to find how many moles of Pb is made from 49.7 g PbO. You multiply the number of moles of product times the enthalpy value given, which gives you the q to plug into your regular q=mC s (Tf-Ti). Once you solve for mass...

abbydouglas1K

Okay awesome thank you !

abbydouglas1K

He does not.

abbydouglas1K

Basically the rate the reaction ((-1/a)(d[A]/dt)) is equal to mol x L^-1 x s ^-1. This rate is equal to the either k[A]^0, k[A]^1, k[A]^2 depending on whether or not the reaction is zeroth order, first order, or second order respectively. [A] represents the concentration of an unknown reactant and t...

abbydouglas1K

In this problem it says that these reactants react in a second order process so that k[H2][I2] is the rate. However I thought that a second order process was k[A]^2 . Does A just represent reactants and the square mean there is two reactants hence a second order process?

abbydouglas1K

In this problem the temperature is given but not included in the final answer. Is the temperature not important ? Why was it not accounted for ?

abbydouglas1K

Basically isolate what you are looking at in the equation to the gases that the question is asking about and then set them equal to each other. If you divide the molar coefficients (what side you solve for depends on what chemical the question is asking about) and you will get the ratio of the rate ...

abbydouglas1K

Thank you!

abbydouglas1K

What TA's review sessions did y'all find to be the most helpful? Because I've gone to a few where I feel more lost when I leave then helped. From the review sessions for the midterm, I found those by Morris, Nathan, and Ronald the most helpful because they were fun and covered the material in a way...

abbydouglas1K

What does it mean for a reaction to be isochoric?

abbydouglas1K

Any isothermal reaction can be assumed to also be reversible In this class.

abbydouglas1K

if you used the constant given for constant pressure 5/2R you should have gotten a value close the actual C that as even about an hour into the test.

abbydouglas1K

If the question says that the pressure is being kept constant(Cp) or that the volume is being kept constant (Cv) you will use 5/2R and 3/2R respectively if the molecule in question is a monatomic gas.

abbydouglas1K

Under what circumstances do we use this entropy equation ?

abbydouglas1K

Has Lyndon announced anything about a practice midterm ?

abbydouglas1K

What does delta H represent? And what does a negative delta H value stand for? I'm sorry I'm just becoming really confused by all these different variables and what exactly it means and when to solve for them.

abbydouglas1K

What exactly is delta U ? I know that it is solved for with q and w but what exactly are we solving when we solve for delta u?

abbydouglas1K

How do we know when we to use ln(V1/V2) ?

abbydouglas1K

For part B of this problem two different constant values of R were used. One was R=.08206(L)(ATM)/(K)(MOL) and the other R=8.3145(J)/(K)(MOL), how do we distinguish when to use this two different constants?

abbydouglas1K

What is the difference between these two ? I saw the chart in the book but I am not sure which one to use when a question is asking to use them.

abbydouglas1K

Okay good to know thank you !

abbydouglas1K

What happens to a reaction at equilibrium when you decrease the volume ?

abbydouglas1K

pKa and pH measure different quantities. pKa measurers acid strength and pH measures H+ concentration, which are similar but Ka is used to find pKa as opposed to a molar cpncenztrartion of H+ ions in a solution.

abbydouglas1K

Kc and Kp are interchangeable they just denote different measuring methods!

abbydouglas1K

Are pKa and the pH the same thing ?

abbydouglas1K

Michelle Song 1G wrote:Under what conditions does it not equal 10^-14? For 6B.9 [H3O+][OH-] does not equal 10^-14...

I ran into this same problem and I am not 100% sure why it does not work because it works for the last two parts but it may be because we can not assume that the values of the temperature are constant.

abbydouglas1K

I'm glad I'm not the only one who thought this because if you do divide Kw by 3.1 mol/l you get a concentration with a value of 10^-15 which I'm not sure is possible

abbydouglas1K

Yes the temperature should be in Kelvin but you must make sure that the temperature stays the same throughout the reaction or the equilibrium constant will be correct.

abbydouglas1K

For part B, since you are technically working with the exponents, you'd have to square root the K to get the answer. Whereas, for part c the coefficients (which become exponents) are doubled so you would have to square the K. So does this mean that every time you have molar coefficients that are le...

abbydouglas1K

I know how to find K but what does it mean ?

abbydouglas1K

Thank you so much I thought it was only based on the overall charge of the compound !

abbydouglas1K

Thank you so much I appreciate it :)

abbydouglas1K

Thank you so much!

abbydouglas1K

How can you tell which is which? I know that string acids apparently pronate in water but how can you tell by just looking at them ?

abbydouglas1K

I had the same problem I looked at the answer book and Im not sure how the equation was balanced just from knowing the product .

abbydouglas1K

Thank you so much this is really helpful !

abbydouglas1K

From what I understand the oxidation number is the number of electrons an atom either loses or gains to fulfill or help another atom fulfill the octet rule. So because Carbon has 4 valence electrons it donates those to another atom to help it fulfill its octet rule, thus giving the carbon atom a +4 ...

abbydouglas1K

For the vsepr model to work you need one central atom and the vsepr shape is determined by the way in which surrounding atoms or lone pair electrons interact with each other around the central atom.

abbydouglas1K

How do we do determine polar and non polar structures from looking at lewis structures ?

abbydouglas1K

Do lone pairs get their own hybridization orbital ?

abbydouglas1K

A lot of the hw problems in the book ask for you to give a VSEPR formula what is that ?

abbydouglas1K

thank you so much !

abbydouglas1K

How do we know what the bond angles are when there re lone electrons pair on the central atom ?

abbydouglas1K

How many molecular shapes are we supposed to be able to identify?

abbydouglas1K

Do the lone pairs around atoms that are not the central atom affect the molecular shape ? For example the hw asks for the shape of CH2F2 and the two fluorine molecules bonded to the carbon have three lone pairs while the hydrogen have none. Do these affect the shape or is it only lone pairs that sur...

abbydouglas1K

When you calculate the formal charge I know that boy the end ll of the each individual changes must add up to the overall charge of molecule/ion. However if they add up does that means it is in its most stable or should you and try and make it so that you reduce the number of formal charges you have...

abbydouglas1K

Question: Which bond is longer ? The CN bond in HCN or in H3CNH2? I know that bond lengths tend to correspond with atomic radius size but does the addition of the extra hydrogens make the molecule necessarily larger?

abbydouglas1K

From what I looked up bond lengths correspond with atomic radius, so the smaller the radius of the two bonded atoms the smaller the overall bond length.

abbydouglas1K

How do we account for electrons in the 3d orbital in our lewis structure ?

abbydouglas1K

annabel 1 1F wrote:How do we know how many resonance structures to draw?

I think you use the amount of possible double bonds between the same atoms to determine how many resonance structures you can have.

abbydouglas1K

How do we know when it is necessary to calculate the formal charge?

abbydouglas1K

How do we calculate the uncertainty of the kinetic energy ?

abbydouglas1K

Have you converted this answer into sig figs ?

abbydouglas1K

Why do the answers have 1 sig fig ?

abbydouglas1K

Don't trust atoms they make up everything.

abbydouglas1K

Im pretty sure this second test will pretty much cover the entire Quantum world unit we've been doing aka the majority if the video modules

abbydouglas1K

This was super helpful thank you!

abbydouglas1K

The problem asks to solve for the wavelength of yrays with an energy of 140.511 keV and I am not sure how to convert these units to joules or if I need to convert them at all.

abbydouglas1K

I know that to solve for the kinetic energy of a photon the equation is Ek=(1/2)mv^2 but where do we find the values of the mass of the specific electron ?

abbydouglas1K

I was stuck on this same problem thank you so much !

abbydouglas1K

This definitely encourages me to attend more step up/peer learning sessions.

abbydouglas1K

I'm pretty sure the phrase formula units is just generic, and varies based on what the question is asking i.e; for someone looking to answer a question about volume the formula units would be milliliters/liters etc. while a question about number of atoms could possibly be moles. I'm not 100% sure th...

abbydouglas1K

I wasn't sure either but for the learning objectives given to us for the basic chem review he only said know the main elements not how to name the compounds.

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