CHEMISTRY COMMUNITY

connie 2C

how do you find k in a concentration cell?

connie 2C

can anyone explain how they got their answer for 1d and 1e for the endgame practice problems?

connie 2C

i know that the final is a take home and open book exam now but how are we supposed to turn it and through what application? for ls30b, jukka is making us scan the test through an app and made us print out a template but does anyone know how lavelle is assigning our test? im just kind of lost...

connie 2C

what's the difference between the last two equations shown on the formula sheet? when do we use which?

connie 2C

what’s the difference between the integrated rate laws vs the general rate law?

connie 2C

you use the experiments to determine the reaction order, rate law, reaction rate, and more when asked. the experiments tell you all the information and is a method of how to solve for those things asked

connie 2C

what is the difference between the unique average rate and the general reaction rate? is it just another way of writing the general rate?

connie 2C

when do you add a negative when determining the rate law?

connie 2C

i found the half life to be 5.204 hours for part (a) but i'm not sure what i'm doing wrong for part (b). my answer is nearly identical to the initial concentration that is given for part b and i know that my answer should be smaller. can anyone that has done the problem help?

connie 2C

is one of the E cell values under standard conditions?

connie 2C

the reactant side of your equation has a H but your product side doesn't. the correct chemical equation includes the H but i'm not sure how they came to that conclusion of the last molecule sorry

connie 2C

E is the nonstandard cell potential and the standard E is the cell potential under standard conditions

connie 2C

the two reactions are a redox reaction but it is easier to analyze the reaction by making them into two half-reactions

connie 2C

for cell diagrams, you're supposed to write them in the order that the reaction occurs (kinda like chronological order if that makes sense)

connie 2C

i don’t understand how to find the n in this equation. where do you look in the given equation to find n?

connie 2C

how come work is equal to 0 in a reversible system?

connie 2C

what is the difference between this equation and the other equations we know? what does it relate?

connie 2C

what happens in a galvanic cell if the reaction was not spontaneous? would there be no change to the cell?

connie 2C

are oxidation numbers the charge of the molecule? will we be needed to calculate the oxidation numbers of larger molecules?

connie 2C

when combining redox reactions, what shouldn't be in the final equation? what should be canceled or changed?

connie 2C

when do you substitute the w=PdeltaV into the first law of thermodynamics?

connie 2C

when there is a constant multiplied to the overall chemical equation, how does Kc change? what are the rules for Kc when there is a change to the overall reaction(s)?

connie 2C

im not sure if you need to use the moles of gas given in this equation because there is a change in volume and the question gives you a constant external force. since those two things are given, you can use w=-P*deltaV to calculate the work done. you would then use the conversion factor to change th...

connie 2C

in one of the organic chemistry tutor's videos, the equation he uses is deltaU=q-w rather than deltaU=q+w. can someone tell me why the sign in his equation is changed?

connie 2C

the standard reaction enthalpy refers to when all R and P are in their standard state at 1 atm. entropy is a state function because the properties are additive and is considered an extensive property because it depends on the number of particles (delta S= KblnW)

connie 2C

those are two of the three methods we learned to calculate enthalpy. to calculate the standard reaction enthalpy, the notes say "if bond enthalpies are not available, one can calculate the standard reaction enthalpy by using the standard enthalpy of formation of all products and subtract the st...

connie 2C

how do you know when the system is reversible?

connie 2C

the question is "calculate the change in molar entropy of carbon dioxide that is allowed to expand isothermally to 10 times its initial volume (treat carbon dioxide as an ideal gas, Cv,m=3/2R)"

connie 2C

for #1, we used the equation delta s= nRln(V2/V1). what is n equal to in the problem? is it equal to 1 because we are calculating molar entropy?

connie 2C

i found these equations on the class website under the constants and equations tab^^

connie 2C

i think we are supposed to use the equations Cv=(3/2)R and Cp=(5/2)R to find the answer since it's not given.

connie 2C

i'm not that good with remembering the letters that are associated with all of the terms. can anyone tell me a list of what each letter represents? like delta u, delta s, etc..

connie 2C

how do you find the amount of microstates a molecule has and what is done with that number afterwards? i didn't understand in lecture today what he was saying about the microstates a particular molecule had was 3^avogadro's number...

connie 2C

sorry the equation is -nRTln(V2/V1)*^

connie 2C

in the second equation, would we ever have to use the integral or would we just be using the equation -nRT(V2/V1)?

connie 2C

what's the difference between R in the equation with volume and C in the equation with temperature? are these constants that are given?

connie 2C

what is internal energy? i don't understand the concept of why q + w equals the change in internal energy

connie 2C

when do you use each equation and how do you know when to use it?

connie 2C

did anyone get the last part of the last slide of friday's lecture? i didn't get the chance to write it down

connie 2C

the notes say:
1. if V decreases and more moles of gas on the left, then reaction shifts right
2. if V decreases and more moles of gas on the right, then reaction shifts left
3. if V increases, no effect on reaction

connie 2C

my ta gave us an equation for the conversion but i don't get why it's different from the equation that lavelle gave in class. my ta gave us Kp=Kc(RT)^Dn where Dn is the "difference in the number of moles of gases on each side of the balanced equation for the reaction; number of moles of gaseous...

connie 2C

when you add two chemical equations together, how do you figure out the new Kc value?

connie 2C

the increasing pressure causes the side with more moles to produce more of the side with less moles. im not sure what lavelle was talking about but that's the concept of his explanation.

connie 2C

when a chemical equation is written and all the reactants and products are gases, do you use Kp rather than Kc? in what cases do you use Kc rather than Kp?

connie 2C

an exothermic reaction releases heat which means heat is a product in a chemical reaction. when you increase the temperature, think of it like you are increasing the amount of product. when more product is added, the equilibrium shifts towards the left.

connie 2C

does an ice table only include gases and does not include solids and liquids?

connie 2C

will the q value eventually reach k? is q the value that is calculated when the reaction is not at equilibrium?

connie 2C

will there be any situation where both values of x from the answers to the quadratic equation are positive? if so what do you do?

connie 2C

does adding an inert gas change/shift equilibrium?

connie 2C

why does changing the amount of moles of a certain molecule not change the partial pressure of the other molecules? i thought since the total number of moles changed, the other partial pressures would change but my ta said they don't.

connie 2C

H3O+ refers to the released H+ ions which makes a solution acidic and water combined

connie 2C

when given the pKa, take the antilog of it to get the Ka value

connie 2C

i didn't find it either but maybe the book has an error and meant to refer to 5E.1 table. maybe try that? or maybe look in the back of the book?

connie 2C

i found someone else who answered the same question and this was their response: (credit to sierra cheslick 2B) "This is a salt, and it dissociates in water. Since Cl- is the conjugate base of a strong base, it is very weak and therefore considered to not affect pH and can be left out of the eq...

connie 2C

if you're a visual learner, i would suggest just going onto youtube and looking up a video to help you because you can actually see what their process is and how they get the answer.

connie 2C

you can go to youtube and search up your topic and there will be tons of videos that help explain the topic. "the organic chemistry tutor" on youtube has a video on coordination compounds so you can watch that and follow along

connie 2C

do we need to memorize the equation for acid rain for the final or would we just need to know the concept of it?

connie 2C

a post from chem mod answered the same question and he said, "Amphoteric is an general term for compounds that can act as an acid or a base. However, there are also compounds (like water) that gain or lose a proton to form an acid or base and this proton is where amphiprotic comes from. Therefo...

connie 2C

can someone explain how to find the conjugate acid/base?

connie 2C

how do you identify amphoteric compounds? are there steps to take to identify them an easy way or?

connie 2C

i feel like you wouldn't need to memorize all of them but knowing some of the common ones or the basic ones would be helpful.

connie 2C

what's the difference between a bronsted acid/base and a lewis acid/base?

connie 2C

how would you know which molecule is a stronger base, BrO- or C17H19O3N? i don't know where to even start so any help would be appreciated

connie 2C

what is the significance of sigma and pi bonds? i don't understand what they do for the molecular structure.

connie 2C

NO is a linear shaped molecule and it's polar because it's not a diatomic molecule and there is a difference in the electronegativity values of those atoms. the difference between N and O is 0.5 which makes it polar too.

connie 2C

if two molecules have only london dispersion forces, how do you know which is stronger?

connie 2C

if you go online and look up practice problems, you should be able to find some that are challenging. you could always do the examples in the book i guess. i feel like as long as you know the concept of sigma and pi bonds, you should be good for the exam.

connie 2C

is bent and angular the same shape? are they just interchangeable names?

connie 2C

what does the a, x, and e stand for in the vsepr formula?

connie 2C

how do you know which forces are within polar/nonpolar molecules? i know that all molecules have london dispersion forces but i don't get how you know when they have dipole-dipole interactions or other forces..

connie 2C

why does SO2 have dipole dipole forces? i don't really understand the concept of dipole dipole forces or how you know when a molecule exhibits it so if someone could explain that would be awesome!

connie 2C

why is a molecule with a higher electronegativity more soluble in water?

connie 2C

the question says "which substance has a higher melting point: CHI3 or CHF3?" the justification in the answer key says that CHI3 has stronger london forces but i don't understand why they justified it like that. can someone explain why CHI3 has the higher melting point and explain the bond...

connie 2C

why does the trend in electronegativity increase when you go up a column and increase when you go to the right in a row?

connie 2C

professor lavelle did an example of one of these types of questions during the midterm review and i noticed that he did the process differently. why does it work to multiply the molar mass of the compound with the decimal of the element (like say there was 26.77% C and then you multiply the molar ma...

connie 2C

how do you know which element in the molecular compound is the one with one lone electron? is it based on the electronegativity of the elements?

connie 2C

in 2d.5, when it states to determine which bonds have the greater ionic character, is it asking the which has the greater difference in electronegativity?

connie 2C

the problem is from the dino nuggets review problem #2 and it says "Glycogen is used as energy storage and can be broken down into glucose when needed. Glycogen’s mass composition is C 43.2% H 6.35% O 50.4% and has a molar mass of about 667 g.mol-1. What is its molecular formula?" when you...

connie 2C

what do you do when the given percents for mass composition do not add to 100%? i remember dr. lavelle saying something that you assume that the unaccounted for percent is usually oxygen but do you just add the unaccounted for percent to the percent of oxygen?

connie 2C

you could think about it as f-d-s-p i guess. for ex, if you wanted the electron configuration for gold (Au), you would write it as [Xe]4f^14 5d^10 6s^1. you would do the same thing for 5f too

connie 2C

the number of valence electrons is 5 because the electron configuration for Sb is [Kr]4d^10 5s^2 5p^3. there are 5 valence electrons because you would add the 2 electrons in the s orbital and the 3 electrons in the p orbital to get 5.

connie 2C

what is the difference between resonance and resonance hybrid? is there a difference?

connie 2C

can you provide an example? if it's just adding formal charges then yes they do cancel out.

connie 2C

there's not many exceptions so i think if you just memorize them, you shouldn't have a problem with it

connie 2C

do we draw lewis structures for both ionic and covalent bonds? how would we draw them for ionically bonded molecules?

connie 2C

how come in some electron configurations the d-orbital comes before the s-orbital like in titanium?

connie 2C

what exactly is a resonance structure? is it a molecule that has multiple lewis structures that can be drawn for that molecule...?

connie 2C

do we have to know all of the different types of lewis structures for one molecule or is there a specific lewis structure that we need to know for each molecule?

connie 2C

professor lavelle said something about how double bond lengths are 1.2 A and how single bond lengths are 1.4 A. how come the bond lengths were 1.24 A for the example from today's lecture?

connie 2C

does the photoelectric effect prove the equations we use like E=hv? i don't get what the photoelectric effect proves?

connie 2C

how do we calculate uncertainty and what equations do you use? i don't really understand much about the concept or what it is used or anything..

connie 2C

also to correct myself in the first post, i meant the equation c=v*wavelength not c=v/wavelength! sorry!

connie 2C

so if you are given frequency, then you would use the equation c=v*wavelength to find the wavelength and then use that to find the energy?

connie 2C

b) First, you convert mg to g 5.00 mg * (1g/1000mg) = 5.00 x 10^-3 g of Na Since, it's asking for the how much energy is emitted by an excited SODIUM, you use the molar mass of Na 5.00x10^-3 g Na * (1 mol Na/ 23g Na) * (6.022 x10^23 atoms Na/ 1 g Na) = 1.31 x10^20 atoms of Na (1.31 x10^20 atoms Na)...

connie 2C

for problem 1B.7, why do we use both c=v/wavelength and E=hv and combine it into one equation? why does using the combined equation give us the energy and not the E=hv equation?

connie 2C

the question asks what happens when the frequency of electromagnetic radiation decreases. is my reasoning correct by saying when the frequency decreases, the wavelength increases which then decreases the overall speed?

connie 2C

when forming equations, how do you know the state of each molecule/compound? is it just common knowledge to know whether it should be aqueous or in gas form?

connie 2C

what's the purpose of finding the limiting reactant in a problem? When you find it, what's the next step you would do?

connie 2C

for part a and b, you would use the molar mass of the element to calculate the number of moles in each sample of the element. for part c, you would use avogadro's number to calculate the amount of moles in amount given.

connie 2C

How do you calculate the moles of an ion in a molecular compound? What conversion factor would be used?

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