CHEMISTRY COMMUNITY

dtolentino1E

i actually do think that there will be hw questions on the exam! it's on the syllabus that the final will include hw questions, and i don't think that is going to change just because it's online.

dtolentino1E

this is especially useful to derive the equation delta G = delta H + w !!

dtolentino1E

i think the problem will specify if the pH is at the initial or equilibrium state of the solution, because you could put that H+ concentration at either point when making your ICE table

dtolentino1E

Ami is correct! The conjugate seesaw means that a weak acid will have a strong conjugate base

dtolentino1E

3/2R and 5/2R are used for monoatomic or diatomic gases like N(g) or O2(g)

dtolentino1E

will we have to come up with intermediates between two rxns, or will they be given to us? and if we have to make them up on our own, will multiple answers be acceptable?

dtolentino1E

what is the difference between a rate law and an integrated rate law?

dtolentino1E

how can you tell which step in a rxn is the rate-determining step/slow step? i get it by looking at a graph or something, but what if you only have the rxn in front of you?

dtolentino1E

i learned a lot by watching this video: https://www.youtube.com/watch?v=irJ4ANrUXPI
he only mentions a little about pre-equilibrium, but i think overall, you will understand the most important aspects of kinetics!

dtolentino1E

the book doesn't really mention any other ways to check your answers, so i don't think we will have to know that

dtolentino1E

i think it would be most appropriate to specify rate of consumption/production of A when you are dealing with multiple rate laws in one problem, or the question specifically asks you to specify

dtolentino1E

for test #2, will we receive a list of all the standard electrode potentials needed along with the regular periodic table/equation sheet? kind of similar to the midterm?

dtolentino1E

i'm pretty sure this has to do with the electronegativity of the element, because some elements in compounds are more likely to attract electrons and have more stable/consistent oxidation states, while something like cardon can be a little more flexible.

dtolentino1E

i think this is referring to the equation ΔG=ΔG∘+RTlnQ

dtolentino1E

for the ones with different oxidation states, i think you would have to think about the context of the rxn that you're using. if you write out the rxn you can calculate the oxidation state of Fe and go from there.

dtolentino1E

redox rxns that aren't acid/base rxns would be like the oxidation of iron: Fe + O2 --> Fe2O3

dtolentino1E

i think you're supposed to calculate n by the number of electrons that need to be transferred in the rxn. so you would have to write out the half-rxns of the cathode and anode, and see that only 1 electron is transferred and therefore n = 1

dtolentino1E

when we combine half-redox rxn like in Hess's law, why can't we also add together the E as if it was delta H?

dtolentino1E

will gibbs free energy be on test 2? specifically, the equations where we connect delta G and Q/K?

dtolentino1E

can someone explain the connection between having a negative or positive EMF and Q? i know that having more reactants in a rxn will make it more spontaneous bc the rxn will want to shift toward products, but how is this related to the potential difference in the cell?

dtolentino1E

how would a galvanic cell have a negative emf?

dtolentino1E

is there also a real-life example for other parts of the galvanic cell, such as the salt bridge?

dtolentino1E

I believe 8.134 is the number used as the gas constant R! For n, we want to use the number of moles in the rxn

dtolentino1E

i think temperature and pressure have to be constant, so that no energy is released as heat or entropy, but all used as work

dtolentino1E

why do exothermic reactions shift to reactants and endothermic reactions shift to products when there is an increase in temperature?

dtolentino1E

how do i know the oxidation states of elements in compounds?

for example, in 6K.1, it says that C is oxidized from -2 to 1- in C2H5OH --> C2H4O

dtolentino1E

will the equation to calculate K using delta G be on the next exam? (Test 2??)

dtolentino1E

A reaction used in the production of gaseous fuels from coal, which is mainly carbon, is C(s) + H2O(g) <--> CO(g) + H2(g). (a) Evaluate K At 900 K, given that the standard Gibbs free energies of formation of CO(g) and H2O(g) at 900 K are 2191.28 kJ/mol and 2198.08 kJ/mol, respectively. (b) A sample ...

dtolentino1E

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood: H+(aq) + Cr2O7 2-(aq) + C2H5OH(aq) <--> Cr3+(q) + C2H4O(aq) + H2O(l) Identify the elements undergoing oxidation or reduction and indicate their initial and final oxidation num...

dtolentino1E

i think the main equation for q is q = n.C.deltaT where C is the heat capacity of the substance you are heating and n can be either grams or moles

dtolentino1E

in the solutions manual, there are three steps to solve this equation: 1. calculate delta S for heat reactants to 100 degrees celsius 2. calculate delta S for the vaporization of H2 at 100 degrees celsius 3. calculate delta S for the rxn when it cools back down to 85 degrees why is it necessary for ...

dtolentino1E

in this problem, we have to use the equation E = hc/λ and calculate the number of photons needed for the rxn
will we have to know this and other quantum equations for the midterm?

dtolentino1E

does anyone know what equations to use when there is the condition that the system is at constant pressure/constant volume? i'm looking for equations related to q, w, delta U, and entropy

dtolentino1E

Suppose that 50.0 g of water at 20.0 degrees Celsius is mixed with 65.0 g of water at 50.0 degrees Celsius at constant atmospheric pressure in a thermally insulated vessel. Calculate Delta S and Delta S(total) for the process. in the solutions manual, the first step is to assume there is no change i...

dtolentino1E

Calculate the standard enthalpy of formation of dinitrogen pentoxide from the following data: 2 NO(g) + O2(g) --> 2 NO2(g); delta H° = -114.1 kJ 4 NO2(g) + O2(g) --> 2 N2O5(g); delta H° = -110.2 kJ and from the standard enthalpy of formation of nitric oxide, NO (see Appendix 2A). how do i calculate ...

dtolentino1E

when a system is at constant pressure, q = delta H because the only energy being released is through heat

dtolentino1E

i think it will be given in the problem if the rxn is reversible or not

dtolentino1E

no, we didn't go over adiabatic processes in class

i think for that question, we are just supposed to know that it's a closed system

dtolentino1E

so in order to calculate delta U, we use the equation delta U = q(v) because it is at a constant volume so there is no work done so we need to figure out the q(rxn) by using the equaiton q(rxn/system) = q(surroundings) where the surroundings is the calorimeter first we need to figure out the specifi...

dtolentino1E

yes!

the change in internal energy (delta U) is usually calculated as heat (q) + work (w), but at constant pressure, q = delta H and w = -P(deltaV)

dtolentino1E

do you know if K will mean Kp on the exam too? or will it explicitly state if we should calculate Kc or Kp?

dtolentino1E

i think it's best to be prepared to write equations for acids and bases. if you know how to tell which compounds are acids and which are bases, then you can determine whether H30+ or OH- is produced (the trick is that acids give off a proton aka produced H3O+ and bases accept a proton aka produce OH...

dtolentino1E

volume and pressure have an inverse relationship, so a decrease in volume = increase in pressure and an increase in volume = decrease in pressure

dtolentino1E

Kw basically means the ratio of products/reactants in the breakdown of water (2H2O <--> H3O+ + OH-)

dtolentino1E

a change in volume doesn't affect K in the long run, only temperature does

dtolentino1E

i think being more thermodynamically stable means that the equation's K value is closer to 1 (meaning that the products and reactants have equal values at equilibrium)

dtolentino1E

I would say you should bring out the ICE boxes when the question makes an effort to distinguish the initial concentrations of R/P and their equilibrium concentrations

dtolentino1E

for these questions, use the morality notation of brackets [] to represent concentration. 1. write K = 2. write [products]/[reactants] and use the coefficient in the equation as an exponent 3. do not write elements or compounds that are solid (s) or liquid (l) for example, in 5H.1 a) N2 +3H2 <--> 2N...

dtolentino1E

I think it's because the coefficients in the reaction are representative of the molar ratio in the reaction, and the K value is basically a ration of the products/reactants by their concentration

dtolentino1E

I don't really think the two will ever be connected in a problem because in limiting reactant questions we are trying to calculate the amount of product that can form by the reactants being fully used in the reaction. But in equilibrium question, we look at both the reaction from reactants to produc...

dtolentino1E

Which is the stronger base, the hypobromite ion, BrO2, or morphine, C17H19O3N? Justify your answer.

for 6C.17, the solutions manual uses the pKb of each base to determine which is stronger. is it possible to tell which is a stronger base without using this calculation?

dtolentino1E

for this question, how do i know that As2O3 and Bi2O3 are amphteric?

State whether the following oxides are acidic, basic, or amphoteric: (a) BaO; (b) SO3; (c) As2O3; (d) Bi2O3.

dtolentino1E

hi! i'm having trouble answering this question:

Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. Write a chemical equation to justify your answer. (a) NH4Br; (b) Na2CO3; (c) KF; (d) KBr; (e) AlCl3; (f) Cu(NO3)2.

dtolentino1E

hi! in the past exam questions review for the final, Lavelle went over a question that asked us to draw the structure of urea, and we also used cisplatin for another question. should we know how to draw all structures for the other biological coordination compounds as well? (myoglobin, hemoglobin, v...

dtolentino1E

what examples of coordination compounds with industrial importance should we know for the final?

dtolentino1E

The coordination number of an atom in a molecule is the number of atoms bonded to the atom. For Cu+, it would simply be the possible amount of atoms that it could bond to.

dtolentino1E

1. When naming a complex ion, the ligands are named before the metal ion. 2. Write the names of the ligands in the following order: neutral, negative, positive. If there are multiple ligands of the same charge type, they are named in alphabetical order. (Numerical prefixes do not affect the order.) ...

dtolentino1E

i think it would be more useful to look at the concentration of H atoms rather than the electronegativity to determine which is the weaker acid. acetic acid is considered weaker because it doesn't dissociate in solution as well as formic acid

dtolentino1E

yes, bronsted acids are also lewis acids. when an acid loses a proton, it gains a lone pair

dtolentino1E

strong acids are completely deprotonated in water, and donates that proton so easily to the conjugate base which means that there's no need for the conjugate base to have any pull on the proton, thus making it weak

dtolentino1E

also, because the ring-like structure of a chelating ligand will cause the cations to bind together really tightly, a compound with a lot of lone pair electrons will easily remove metals from a solution

dtolentino1E

can an acid only be a bronsted acid or a lewis acid, or can they fall into both definitions? we learned that HCl, HBr, HNO3, and so on were bronsted acids because they loose a proton to a base, but can we also qualify any of them as a lewis acid (do they accept lone pair electrons?)

dtolentino1E

how does the carboxyl group on C6H5COOH make the compound acidic?

dtolentino1E

how do i find the oxidation state of a transition metal? so far, i've been confusing it with formal charge, but i know the two are different

dtolentino1E

what should we know about myoglobin and hemoglobin? Dr. Lavelle went through a lot of information about these two molecules, but i'm unsure of what parts are important for the final

dtolentino1E

is writing "less than 109.5" an exceptable answer, or do we have to give a specific number?

dtolentino1E

hybridization happens when electrons of a molecule are promoted. it doesn't happen for every molecule, only which if the overall change is toward lower energy with higher energy electrons

dtolentino1E

do nonpolar covalent bond only have london dispersion forces? or can they have any of the other molecular forces?

dtolentino1E

how do induced dipoles happen? and what are some examples of a dipole-induced dipole molecules?

dtolentino1E

hi there! i was just wondering how to tell the difference between a tetrahedral molecule and a triangular pyramidal molecule, or if they can sometimes be interchangeable. I remember from the textbook that lone pairs are considered significant regions of high electron configurations just like bonds. ...

dtolentino1E

their valence shells are 1s and 2s, which don't even have enough orbitals for eight electrons. these elements are stable with just 2 (H, He) or 4 (Li, Be)

dtolentino1E

resonance structures occur when you can shift the bonds in a molecule around. i think you're talking about created an entirely different lewis structure, which wouldn't be considered resonance.

dtolentino1E

a higher boiling point means that the elements in the molecule are highly attracted to each other i.e. the intermolecular forces are strong. because AsF3 is a polar molecule (F, as the most electromagnetic element, creates a dipole) the bonds between the elements are stronger and will take more ener...

dtolentino1E

i know i remember by the acronym FON (the elements fluorine, oxygen, and nitrogen)

dtolentino1E

Alexa is right, it is everything we have learned up until the exam

dtolentino1E

i don't think you have to check formal charge for every structure, just when the question asks you to. For drawing lewis structures, I think it's more important to fill up an octet than it is to have low formal charges

dtolentino1E

4s is considered lower energy than 3d

dtolentino1E

What makes something a Lewis acid/base? And what do coordinate covalent bonds have to do with acid-base rxns?

dtolentino1E

radicals affect the body at a cellular level because they are very reactive and will react with DNA, causing it to mutate

dtolentino1E

Hi! Could someone please explain the connection between polarizability and covalent character in an ionic bond? Also, does electronegativity play a role in a bond's covalent/ionic character as well?

dtolentino1E

the Rydberg equation is usually used to calculate the wavelength of a spectral line, but in hw problems we've also used it to find the energy level n1 or n2 of a certain line. the only constant is the Rydberg constant, which is explained above, but there's also the energy levels n1 and n2, which cor...

dtolentino1E

since we've been drawing all of the lone pairs in class and in hw, it's safe to say that yes, you will have to draw those for the exam. however, i remember some teachers using a line instead of dots to represent lone pairs, so if you want to find alternate ways to draw your lewis structures just tal...

dtolentino1E

yes, the midterm is cumulative, so we will have all the topics discussed in class up until the day before the exam. if you want to know what are popular topics/questions on the midterm, i would recommend finding old exams to practice or just look at. they have a lot available at sac, or a couple onl...

dtolentino1E

i think it's less about what factors are most important, and more about what factors are the strongest, i.e. what forces holds the bonds together the best. also, you have to think about how these factors are kind of like products of one another and are interrelated (for example, because of an increa...

dtolentino1E

from what I understand, you can substitute this kind of structure for the lewis structure at any time, because it's an organic compound, and this is just another way of representing the compound. I know he said we wouldn't be doing much o-chem this quarter, so I wouldn't worry about it

dtolentino1E

hi! on some of the hw problems we've had to use the mass of an electron/proton/neutron in certain calculations, will it be necessary to memorize those values for an exam, or will they be on an equation sheet? thank you!

dtolentino1E

n, l, and m are all quantum numbers n = principle quantum number - it measures energy and size of an orbital, also called the "shell" - it has values of integers (0,1,2,3,4...) l = angular momentum quantum number - it measures shape of an orbital, called "subshell" - it has value...

dtolentino1E

hi! would someone please walk me through their steps for this problem? The velocity of an electron that is emitted from a metallic surface by a photon is 3.63 e 3 km.s^-1. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the metal until the frequen...

dtolentino1E

no, i don't think we have to know how these equations were derived for this class, because the math behind that is much more advanced than what we're supposed to know. just be sure you know the concepts behind each equation and how to apply it to problems!

dtolentino1E

thank you, this is very helpful!

dtolentino1E

technically yes, i guess it doesn't really matter which space you put your first arrow bc it's in the same orbital/subshell, but i think it's best that you just fill it in from left to right just so it's less confusing that way!

dtolentino1E

hi there! i believe it is because the wavelength of macroscopic objects is just too small. if you look at the De Broglie equation, wavelength = h/mv, the larger the mass, the smaller the wavelength will be because planck's constant is divided by mass. when the wavelength is just that small, then the...

dtolentino1E

absolutely it is most effective to do all the hw problems on the list! i think you get a more thorough understanding of the concept that way, and you feel more familiar with the calculations and equations.

dtolentino1E

hi guys! my question is about what you all seem to find is the best studying strategy for this class. so far i've been watching youtube videos along with just taking notes during lecture and reading/doing hw problems from the textbook, but i'm curious to see what other methods people use to study th...

dtolentino1E

hi there! the work function is the amount of energy needed to remove an electron from a metal surface i think more often than not it will be given in hw problems, but if there comes a time when you need to calculate it, it should be quite easy if you use the equation from lecture ( the work function...

dtolentino1E

hi! so when you are trying to calculate the molecular formula and you are given the empirical formula and the mass of whatever compound, i know that you're supposed to calculate the molar mass from the empirical formula and find a ratio between the masses, then multiply by whatever number it comes o...

dtolentino1E

basically, yes.
for net ionic equations, you want to take out the elements of which don't form a precipitate in the products. these are called "spectator ions", because they stay dissolved in the aqueous solution as both a reactant and a product.

dtolentino1E

hi there! if you balance the equation, i believe it actually comes out to 4 molecules of NH3 for 5 molecules of O2. 4NH3(g) + 5O2(g) ---> 4NO(g) + 6H2O(g) because of this, when you calculate moles of reactants, you must take into account the molar ratio of these molecules before deciding the limitin...

dtolentino1E

hi! even though formula writing isn't specifically mentioned in outline 1, i think it's implied that we should be able to write out formulas from symbols and vice versa, because one of the bullet points is to be able to "Write symbols for the elements, given their names, and vice versa". i...

dtolentino1E

hey guys! i have a question for #25 in the G section for fundamentals. it's asking how many molecules will be present in 10. mL of the final solution after diluting 10. mL with a concentration of 0.10 mol L^-1 90 times. i remember a key concept was that moles stays the same during dilutions. does th...

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