CHEMISTRY COMMUNITY

Nick Fiorentino 1E

The original equation has 2e- but since every molecule has a stoichiometric coefficient of 2 you can divide the equation by 2, so n=1 instead of 2

Nick Fiorentino 1E

One way to think of it is remembering the saying "a chain is only as strong as its weakest link". So, if you make the fast step faster, it won't change the fact that the slow step is still slow, which makes the reaction slow, or the "chain weak". In order to make the reaction fas...

Nick Fiorentino 1E

Will we be asked to assess third order reactions on the final? There are a few assigned homework problems which involve them. I think I remember Dr. Lavelle saying we wouldn't address them in this class, but there are assigned problems involved third order reactions

Nick Fiorentino 1E

I'm sure it does change but for the purposes of this question I don't think it matters. That may be a topic addressed in more advanced classes but this class seems to simplify thermodynamics to a certain extent, because it is a really complicated topic

Nick Fiorentino 1E

I think if you're only given one thing (like mass) then you have to plug it in and it will work as long as you are using like values

Nick Fiorentino 1E

How do you know when you need to substitute in the rate law? I.e. like the last example in Dr. Lavelle's review slides

Nick Fiorentino 1E

There are multiple ways to get the answer, Van't Hoff's equation is one, but you can use △G=-RTlnK and just change the T value when solving for K which would give you K at that temperature

Nick Fiorentino 1E

Yeah, as the previous poster said you dont need to include H2O because it is assumed to be in the equation. But, if there is another liquid, you do have to include it. Additionally, if the two reactions occur in the same solution, then you have to add Platinum (Pt)

Nick Fiorentino 1E

Yes, you need to convert Torr into atm. The conversion is 1atm=760 Torr

Nick Fiorentino 1E

G=H-TS

Enthalpy (H) and entropy (S) take into account stoichiometric coefficients, so I guess you could say that G requires you take into account stoichiometric coefficients. However, when calculating G in regards to electrochemistry, you do not take them into account.

Nick Fiorentino 1E

What is electrolysis and how does it apply to what we've learned about redox reactions, etc?

Nick Fiorentino 1E

You add electrons to balance the charges of either side of the reaction. Also, you have to multiply an equation by a number sometimes in order to get the electrons in both half reactions to cancel out

Nick Fiorentino 1E

What causes corrosion and how is it an example of a redox reaction?

Nick Fiorentino 1E

I think the strongest oxidizing agent is the one that has the most positive E value. So, for example Ag+ + e- -> Ag (E=.80V) and AgBr + e- -> Ag + Br-(E= .07V). In this case, the first reaction is the better oxidizing agent

Nick Fiorentino 1E

I think it's best to keep oxidized molecules on the left and reduced on the right because this is how you write out cell diagrams (oxidized II reduced)

Nick Fiorentino 1E

The solution is simply substituting variables; standard delta G = -RTlnK to give the equation Delta G= -RTlnK + RTlnQ. I don't believe it has anything to do with equilibrium

Nick Fiorentino 1E

What about for the transition metals? How do you determine the charges of those?

Nick Fiorentino 1E

In class it was said that E was an intensive property. What does that mean and what are the implications for our use of E and calculating it?

Nick Fiorentino 1E

You’d use the equation G=-RTlnK. You want to solve for K so you’d rearrange the equation to be -G/RT=lnK. You have all the values needed besides G which you can get from appendix 2A, and then you solve for K!

Nick Fiorentino 1E

I would assume not if it’s not in the outlines on the class website. There’s a lot of topics in the book that aren’t taught so just look at the syllabus for clarification

Nick Fiorentino 1E

I think it's important to convert C to K just to be safe; a lot of times using K will make it so the units cancel, so I just always convert C to K to be safe

Nick Fiorentino 1E

How do you go about solving problems asking for the partial pressure of the reactants/products? Would you solve for the partial pressure first and then complete the ICE table or...?

Nick Fiorentino 1E

using 3/2R is for if there is constant volume in the process

Nick Fiorentino 1E

The two red molecules only have to be opposite of each other; so, they can be in the orientation shown in the diagram, or they could be on the horizontal plane, across from each other in two different ways

Nick Fiorentino 1E

Maybe it's because the heat can be given off from the copper block?

Nick Fiorentino 1E

Since entropy is a state function, Delta S could be equal to zero if you return to your "starting point". So, if you increase the volume of a container containing gas and then compress it to its original volume, delta S would be zero

Nick Fiorentino 1E

Today in lecture, Dr Lavelle had a slide going over entropy in phase changes and one equation on that page said q(rev)/T=deltaH/T. Can someone please explain this concept?

Nick Fiorentino 1E

Yeah, whenever a system loses energy in whatever form, that value will be negative. But, that energy must go somewhere else so the energy will be absorbed by another system, so it will be positive for that system

Nick Fiorentino 1E

Can someone please explain what the 3rd law of thermo says? I wasn't quite clear on it when Lavelle explained it, I felt like it was very brief. Thanks!

Nick Fiorentino 1E

In addition to the previous poster, since the reaction is isothermal, the temperature is constant, so the heat can slowly enter the system and offset the energy lost by work. It's important to note that this happens when the reaction is isothermal

Nick Fiorentino 1E

Do you mean w= -nRTln(V2/V1)? This equation comes from taking the integral of (nRT)(dV)/V. You can pull the constants out in front of the integral sign so you have -nRT multiplied by the integral of dv/V from V1 to V2, which is ln(V2/V1)

Nick Fiorentino 1E

What is the difference between irreversible/reversible reactions? Can someone please give an example?

Nick Fiorentino 1E

How do you know when a compound is in its purest form, aka when it won't impact enthalpy change?

Nick Fiorentino 1E

The temperature must be high enough to cause the phase change but not high enough to cause the system to change temperature

Nick Fiorentino 1E

For this equation, will n always be in moles? In the book solutions, I've seen both moles and grams used and am not sure when to use which

Nick Fiorentino 1E

In the solution, it shows q(reaction) equal to -q(calorimeter). Why is this? And how do you know when to use this method?

Nick Fiorentino 1E

K is represented by the products/reactants. So, if K is really small (less than 10^-3) then there are more reactants than products

Nick Fiorentino 1E

How do you know when it's appropriate to make a buffer? As in, what in a question tells you you need to make a buffer?

Nick Fiorentino 1E

A state property does not depend on the path taken to obtain that state. Some examples are energy, pressure, volume, and temperature

Nick Fiorentino 1E

https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/752/2016/09/26195026/ating-20curve-20of-20water.jpeg maybe this picture of the heating curve for water will help. As the previous poster said, it requires a lot of energy to turn water into a vapor which is why steam can cau...

Nick Fiorentino 1E

Lavelle gave an example of creating a buffer in class so I would think it's possible for it to be on the test, or even the midterm and final

Nick Fiorentino 1E

How does a reaction respond in response to pressure? I was confused when Lavelle was explaining this in class

Nick Fiorentino 1E

When do we have to find the partial pressure for the gases involved in an equilibrium problem? There are gases in essentially every equilibrium problem but their partial pressures are not always calculated.

Nick Fiorentino 1E

What does it mean in terms of which way the reaction will proceed if Q is less than K? Greater than K?

Nick Fiorentino 1E

To find x, you would set .133-x (the statement for the final H2 concentration) equal to .40 x .133mol/L because 60% of the H2 was used, so 40% remains

Nick Fiorentino 1E

How do you tell if a gas is an inert gas?

Nick Fiorentino 1E

solids/liquids aren't included in the equilibrium constant because their concentrations don't change enough to affect K

Nick Fiorentino 1E

Using "x" in the ICE tables would definitely be helpful if the problem is complicated enough, but if it's simple and you can figure out the change without variables, that might be easier

Nick Fiorentino 1E

I understand the initial and equilibrium rows in the ICE box but how do you figure out the change row? That is, how do you figure out what the change in concentration will be?

Nick Fiorentino 1E

What does the unit bar stand for in problem I5? Is it just another unit for pressure?

Nick Fiorentino 1E

when do you write the equilibrium constant as Kc as opposed to Kp?

Nick Fiorentino 1E

Yes, only species with odd numbers of electrons are radicals (ex CH3 has 7 valence electrons so it is a radical)

Nick Fiorentino 1E

What is the relationship between Bronsted and Lewis acids and bases? Can a molecule be both?

Nick Fiorentino 1E

what can make london forces stronger?

Nick Fiorentino 1E

What makes it possible for a chelate to form and how could you tell if it was possible?

Nick Fiorentino 1E

What are the functions of Cr, Fe, and Co in biological systems? And how deeply will we be expected to know how they perform their function?

Nick Fiorentino 1E

I don't think there's any specific reason why sp3 is focused on. It is very common but there isn't anything special about it as far as I know.

Nick Fiorentino 1E

Bronsted acid: a species that donates a proton Bronsted base: a species that accepts a proton Conjugate base: what is left over after an acid donates a proton Conjugate acid: what is formed when a base accepts a proton Bronsted acids have conjugate bases and Bronsted bases have conjugate acids. In t...

Nick Fiorentino 1E

KA x KB= KW

So, as KA increases, KB will decrease. As KB increases, KA will decrease. The two values must always equal KW so they will change in accordance with the concentration of one another.

Nick Fiorentino 1E

For me, I had trouble with knowing how c and d were amphoteric. Metalloids are amphoteric and they are marked on the periodic table as the elements that are between the metals and nonmetals; they follow a diagonal band.

Nick Fiorentino 1E

At the end of class Lavelle said that something about weak acids and bases affecting pH... did he say that weak acids and bases DO affect pH or do NOT affect pH? I didn't catch it. Thanks!

Nick Fiorentino 1E

When is it appropriate to use the English and latin name of an element when naming a coordination compound?

Nick Fiorentino 1E

Resonance structures cause the length of a bond to change slightly. Although there are multiple lewis structures for resonance structures, the true structure of the molecule is a blend of the resonance structures. This means the bond lengths are a blend between single, double bonds, causing the bond...

Nick Fiorentino 1E

Yes, the most important thing is to draw the Lewis structure correctly and then from there it should be simple using the rules the previous poster stated to count the sigma and pi bonds

Nick Fiorentino 1E

T- shaped has a trigonal bipyramidal arrangement, but has 2 lone pairs and 3 bonds (AX3E2). Trigonal pyramid has a tetrahedral arrangement but has one lone pair and 3 bonding pairs (AX3E)

Nick Fiorentino 1E

What are the bond angles for Trigonal Bipyramidal and octahedral arrangements when they have one and two lone pairs? i.e. bond angles for seesaw, t shaped, square pyramidal and square planar?

Nick Fiorentino 1E

What are the strongest intermolecular forces in order? I know induced dipole-induced dipole is the weakest but where do the other forces fall into the ranking of strongest intermolecular forces?

Nick Fiorentino 1E

What shape would you get if a molecule with an octahedral arrangement has one lone pair? Two lone pairs?

Nick Fiorentino 1E

All molecules can have induced dipole-induced dipole bonding, even polar ones. Problem 3f.1 in the book is an example of this. Part (a) and (d) are listed as being able to have induced dipole-induced dipole interactions along with dipole-dipole interactions

Nick Fiorentino 1E

The structure of this molecule would have Se at the center and 4 oxygen's around it, then hydrogens bonded to the oxygens. This causes the molecule to be polar because O and H have a significant enough electronegativity difference to cause a polar bond. Therefore this molecule can have dipole-dipole...

Nick Fiorentino 1E

What intermolecular forces cause higher boiling points? Lower boiling points? And what are some examples?

Nick Fiorentino 1E

Yes, hydrogen bonding is a type of dipole-dipole interaction. It is not as strong as covalent or ionic bond

Nick Fiorentino 1E

Larger molecules are more polarizable because the electrons in the outer shell are easier to take away. This is because they are "shielded" from the nucleus by the other electrons so they can be taken away from the atom easier.

Nick Fiorentino 1E

In lecture on Friday, Lavelle said that if an atom is highly polarizable, it is solid at room temperature. Why is this?

Nick Fiorentino 1E

Why does hydrogen bonding explain higher melting points? I missed Lavelle's explanation on why this was the case

Nick Fiorentino 1E

Electronegativity increases up a column and left to right across a period. The noble gasses are exceptions because they have a full octet so they are not trying to take any electrons. One way to think of electronegativity is how bad an atom wants an electron.

Nick Fiorentino 1E

Does anyone have any advice for figuring out the various resonance structures?

Nick Fiorentino 1E

What do each of the rules for electron configurations ( pauli's, hund's, aufbau) mean and what would and electron configuration look like if you violated them?

Nick Fiorentino 1E

What do each of the rules for electron configurations ( pauli's, hund's, aufbau) mean and what would and electron configuration look like if you violated them?

Nick Fiorentino 1E

Last night in the review session with Lyndon, it was said that Nitrogen has a higher electronegativity than oxygen. Can someone explain why this is?

Nick Fiorentino 1E

yeah, I don't think we need to know exact cutoffs but it is important to know in what range visible light is and the ranges for infrared and ultraviolet. ultraviolet light is less than 400nm and infrared is more than 700nm. You don't have to state any info about the light type or if its visible unle...

Nick Fiorentino 1E

The elements in period three and the subsequent periods along with the column 13 elements are exceptions to the octet rule

Nick Fiorentino 1E

Yes, it is [Ar] 3d^10 because Cu+ loses an electron. When this type of situation comes up, you always remove or add an electron from the outer shell

Nick Fiorentino 1E

So far the only exception to the octet rule that we've learned is that atoms in period 3 and higher can have more than 8 electrons in their outer shell due to the possibility of having a d orbital (as l can equal 0,1, and 2 when n=3)

Nick Fiorentino 1E

Yes, you use FC = V - (L + S/2). Not all structures will have a formal charge equal to 0 but you want to find the structure that is closest to that value. Also, remember you have to find the formal charge for each atom

Nick Fiorentino 1E

Like the previous poster said, delocalization is when there is resonance in the structure of the molecule. You know an electron is delocalized when it is possible for structures to have multiple bonds in different locations (ex. NO3 example from class; the double bond with nitrogen and oxygen can be...

Nick Fiorentino 1E

The formal charge is the charge on each atom and it is calculated after a Lewis structure is made. They are useful to calculate so you know "good" you structure is; the closer the formal charge is to zero, the better the model

Nick Fiorentino 1E

The energy required to remove the electron is added to the electron's kinetic energy because you need the total energy that caused the electron not only to be ejected but to be ejected at 3.63 x 10^3 km/s. So, because the electron was ejected at that speed, the energy required to eject it is added t...

Nick Fiorentino 1E

Is there a trick to remembering what all the orbital shapes look like? As in, is there a method to remembering what dxy, dy2, d2x,dx2y2, etc all look like?

Nick Fiorentino 1E

I agree with the previous post, but to simplify it, being in a vacuum means there are no outside forces working on a given thing.

Nick Fiorentino 1E

For part c and d, how would you go about determining the values asked for from the given state of the electron? I guess my bigger question is how would you figure out values of n,l, and ml from a given 6d subshell, or something like that?

Nick Fiorentino 1E

What do the +1/2 and -1/2 mean with regards to spin state? Is it the direction in which the electron spins? And how would the spin state be determined?

Nick Fiorentino 1E

The equation for the uncertainty equation is (delta p)(delta x)>(h)/(4pi), where h is planck's constant of 6.63x10^-34, delta p is the spread in values of momentum, and delta x is the spread in values of distance.

Hopefully that helps with the mathematical representation.

Nick Fiorentino 1E

It can be, as, just like various atoms, various molecules absorb different types of light, just like atoms.

Nick Fiorentino 1E

Wavelike properties can be seen in very small things (like an electron) with a high velocity. This why wavelike properties are noticed in electrons, and not other objects like a car. All things have wavelike properties but they are not detectable. In the car example, it is too large for its waveleng...

Nick Fiorentino 1E

Most of the equations we've learned to apply to EMR, but as others have said, not the De Broglie Equation. Something that may help you remember this is that most of the equations we've learned have similar or related variables and the De Broglie equation involves mass and velocity (momentum) so they...

Nick Fiorentino 1E

I believe you only find the percent yield if it is asked in the question, but there may be some scenarios where you need it for a step in the problem. Also, questions don't always explicitly ask what they want you to find so be aware of that

Nick Fiorentino 1E

For problem M15, how would I go about this problem? Not really sure where to start

Nick Fiorentino 1E

For this problem, how would you write its chemical formula? I understand the corresponding compounds for carbon dioxide, oxygen, and water, but I'm not sure about the aqueous solution part of the products.

Nick Fiorentino 1E

I'm a bit confused on how to go about this problem. Does anybody have any hints or ideas? How would we know what the oxide is?

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