CHEMISTRY COMMUNITY

Osvaldo SanchezF -1H

Well to determine what the units should be for these problems it is quite simple. The best way to determine what it should be is to see what the overall order of the reaction is. For problem c we see that the overall order is 5 and thus the units should be M(molarity)/(M^-5*s) or M^-4/s or L^4/(mol^...

Osvaldo SanchezF -1H

Well the solution is is that it must equal 1 so that means that the only value that will yield you 1 is if you put 0 as the exponent and therefore the order is 0 and does not play a role in finding the order of the other reactions. Any value to the power of 0 is 1.

Osvaldo SanchezF -1H

Well because the electrodes theme-selves are solids they are not included in the reaction to find the equilibrium constant so therefore any manipulation in the cathode means that there will be no change in in the cell potential. Also cell potentials are intensive.

Osvaldo SanchezF -1H

The units do represent the rate constant but I would like to add that this is different to the total order of the whole reaction as a whole. You would add all of the constants to get the overall order. Do not forget to make that distinction.

Osvaldo SanchezF -1H

I believe that if you email your T.A. I am sure that they would not have a problem in sending you your exam or even might set up an alternative. Email your T.A.

Osvaldo SanchezF -1H

Intermediates are products that are formed in one reaction that are then used in another reaction to create the new products wanted. So therefore they are made and consumed so that means they should not be present in the final rate law.

Osvaldo SanchezF -1H

When writing a cell diagram always follow the rule of (s)|(g)|(aq)||(aq)|(g)|(s) and you can not go wrong. As you can see that according to this format you do not include liquids so this is the simplest way to know that you would not include H2O.

Osvaldo SanchezF -1H

From my understanding Lavelle has the majority of input on the test and especially the midterm/final. According to some T.A.'s he did not ask for their help for the first midterm that we took. So if anything, it would be important to do know what lavelle wants us to know.

Osvaldo SanchezF -1H

Well something to keep in mind is that many of the problems show different placement of the compounds such as including liquids or putting solids before aqueous solutions. You should not mind these type of problems and always stick to the rule of (s)|(g)|(aq)||(aq)|(g)|(s). My T.A. told me that not ...

Osvaldo SanchezF -1H

Well for an E cell to do work its value has to positive. To find the value for cell potential it would be Ecathode - Eanode and so if cathode is larger then it will yield a positive value.

Osvaldo SanchezF -1H

You would take the instantaneous rate over the average rate because it is more accurate since it is the rate at one specific time instead of that at an interval which would lead to a greater margin of error.

Osvaldo SanchezF -1H

Well we know that Cl2 is both the reduced and oxidized form and we have the oxidized form so therfore the reduced form must be
Cl2 + 1e--->Cl-

Osvaldo SanchezF -1H

I don't believe this scenario is possible because a redox reaction is a reaction that must include both an oxidation or reduction and if it does not meet this criteria then its not a redox RXN. However one molecule can be both oxidized or reduced not just reduced.

Osvaldo SanchezF -1H

Well when it says electrolyzed it refers to the use of eternal energy and that occurs when a reaction is non-spontaneous.

Osvaldo SanchezF -1H

We might be asked to do this but in the form of s|g|aq||aq|g|s and not an actual picture.

Osvaldo SanchezF -1H

well in a cell diagram a cathode is termed to be to the right and an anode is termed to be to the left of a cell diagram, well usually. Best way to determine which reactions belongs where is to know that in the cathode reduction half reaction takes place and in an anode a roxidation half reaction ta...

Osvaldo SanchezF -1H

One good way to remember this was by using the acronyms LEO goes GUR where LEO stands for losing electrons is oxidized and GUR stands for Gaining electrons is reduced.

Osvaldo SanchezF -1H

Well it is the only molecule present and there is no charge so therefore it must be 0.

Osvaldo SanchezF -1H

One is in scientific notation and the other is not so its the same number just in a different format.

Osvaldo SanchezF -1H

I get that answer to and even if you follow their work the answer should still be 2.7kJ so it must be a typo.

Osvaldo SanchezF -1H

As many already mentioned, the equation is given but knowing how it was derived can help understand it better. So if you are given steps of the derivation then you will know how to manipulate the problem to get what you need.

Osvaldo SanchezF -1H

I will just add that if something is isothermal then the total entropy will also be 0 because since the temperature will be the same the same amount of molecules will be present at any one time.

Osvaldo SanchezF -1H

Since both cases are isothermal, you can assume that delta U is 0. Work is calculated differently in these two scenarios because during an irreversible expansion, there is a large difference between the internal pressure and the external pressure, so expansion occurs quickly. This is why we can use...

Osvaldo SanchezF -1H

Something could be isothermal reversible or isothermal irreversible and the way to solve them both is the same when finding entropy as entropy is a state function but different when finding work because it is not a state function. Another difference is that in an irreversible function take into acco...

Osvaldo SanchezF -1H

There is free expansion occurring in the system which is also known as vacuum and there for no work is done and for some problems it will be combined with an isobaric system so if deltaU and work is 0 then q is 0. This way you apply all concepts and how they all relate to each other.

Osvaldo SanchezF -1H

I believe that it is because we will assume that pressure is constant and therefore delta H=q.

Osvaldo SanchezF -1H

If you want to do it in terms of product or reactant it would also be in terms of KJ/mole and that is called the heat of formation for the product or reactant.

Osvaldo SanchezF -1H

We should also know when it is isochloric, and isobaric. A question might state this and we would have to know what it means. Isochloric means that it has constant volume and isobaric is when the pressure is constant. Also a key not to remember for isothermal is that because there is no change in te...

Osvaldo SanchezF -1H

Water has different specific heat depending the state that it is in. 4.18 is just for when it is in liquid form. But the problem says ice which is water in its solid form which would be 2.03. Take this into account for future problems.

Osvaldo SanchezF -1H

Instead of a piston you can think of a ballon where you do work on it by blowing air into it. Initially the ballon has a fixed volume and when you blow air the volume will increase and stay at a fixed amount (at least when you tie the not. So then you can apply the irreversible equation for work w=p...

Osvaldo SanchezF -1H

Yea the answer cannot be 900J because that would not make sense. if the change in internal energy is a + 982 and the supplied energy energy is also a + 492 then the equation would be +982= +492+ w where if you do math the work would have to be +490. My book also showed this as the answer(solution Ma...

Osvaldo SanchezF -1H

You cannot really assume anything. It all depends in the problem and the information that they give you. As the person above said though, most reaction occur in the situations that they mentioned unless the question says otherwise. And besides the pressure being constant, it can say that the volume ...

Osvaldo SanchezF -1H

The universe is a system that has no surroundings to which heat or matter for that fact can be exchanged. This exactly the properties that make a system isolated. So the universe is isolated because heat or matter can't be exchanged? SO an isolated system means that heat can't be transferred to the...

Osvaldo SanchezF -1H

A bomb calorimeter is just as you said, its a device used to measure specific heat. The container is made by a metal that does not readily conduct heat. So it's an isolated system in which they add water or oil and have temperature readings outside the container. They run electrical current through ...

Osvaldo SanchezF -1H

The universe is a system that has no surroundings to which heat or matter for that fact can be exchanged. This exactly the properties that make a system isolated.

Osvaldo SanchezF -1H

Pressure is not negative but rather the role value acquired from PdeltaV is. It would depend on the wording of the question. If work is done "by" the system then you should know that the work will end up being negative because it leaves the system but if work is done "on" system ...

Osvaldo SanchezF -1H

Midterms topic usually include whatever Lavelle last covered. He will let us know before the test.

Osvaldo SanchezF -1H

It is as the person above explained in the essence that all the work that is produced by the system is never lost to the surrounding so therefore non of the energy leaves the system. This could be in examples of fully insulated systems where work is produced but due to the walls the energy never lea...

Osvaldo SanchezF -1H

When there is no expansion or compression, then the system is doing no work or no work is being done on the system so therefore Work would equal to 0. This means that Delta H would only be impacted by (+/-)q.

Osvaldo SanchezF -1H

You do not include solids or liquids when finding the equilibrium constant at all. So we do not put anything for it in the ICE table or even just cross it out. It is not wise to put a zero for it because you put zero for the initial concentration of the molecules that are not given but must be inclu...

Osvaldo SanchezF -1H

A solvent is what you used to dissolve another substance and that substance tends to be a liquid of some sort. So if it stated that the state of the molecule is liquid you don't include it in finding's the equilibrium constant. Solvent=(usually) liquid. You don't uncle pure solids as well so anythin...

Osvaldo SanchezF -1H

If you are asking it in term of a question, they would have to tell you that a change in pressure was caused by an inert gas or maybe by a change in volume. Saying that pressure changed(increased/decreased) is not enough to tell whether the equilibrium shifted. They would have to say that it was due...

Osvaldo SanchezF -1H

Percent ionization is just the value for the amount of reactant that was used from from the initial concentration to make products which is usually labeled as x. Then you would divide it by the total initial concentration(there can be multiple initial concentration if there are than 1 reactant and j...

Osvaldo SanchezF -1H

Well since one of the primary focuses of the test was acids and bases and was the last thing we covered that would be included In the test, I do not see why it would not be included.

Osvaldo SanchezF -1H

This is true when the water is at 25*C .

Osvaldo SanchezF -1H

The reason that you don't get the right answer is because you have your Ka as the wrong value. If you look at the table from 6C.2 you notice that the Kb of CH3NH2 is equal 3.6*10^-4 but this is a base and we are given its acidic form so all we have to do is find the Ka of the acidic form of CH3NH2 w...

Osvaldo SanchezF -1H

So when you compress a system it just means the the volume of the system is being decreased. So it would want to shift to the side with less moles but since in this case both sides have equal number of moles, it would not shift in either direction and remain the same. You can think of it as, smaller...

Osvaldo SanchezF -1H

So you do not need to convert to partial pressure though you can if you want but its a waste of time since they gave you the concentrations already. And knowing the equilibrium values of HI and I2 and the K value you don't have to do the ICE table and can just plug in the values to the equilibrium c...

Osvaldo SanchezF -1H

The important aspect of finding the equilibrium constant is to see how much reactant is converted to product so to do that, you find the ratio. So even if you do the conversion it will not matter because the changes in the reactant and product will be the same so therefore the same ratio will still ...

Osvaldo SanchezF -1H

The cutoff to apply the 5% rule is if it less than 10^-3, as that is what he mentioned in class, and then test the percentage of ionization or how much reactant got converted to product. If it Is less than 5% the approximation is sufficient enough if not then you have to use the quadratic. However i...

Osvaldo SanchezF -1H

I am quite certain that we will have to know how to convert to pH when we have the concentration as Lavelle has put a great emphasis on this and the test are based usually on what we learned the previous week.

Osvaldo SanchezF -1H

When we have concentration and if they are gases we wish to convert the concentrations given into pressure or it could be the other way around but for most problems we will use it to find the pressure of molecules when given the concentration when we wish to find Kp.

Osvaldo SanchezF -1H

Will we be expected to sometimes use the approximations, or will we be able to just to use the quadratic formula instead? If it is a quadratic equation then yes but this technique is most helpful when you have a cubic equation. It would be impossible to solve for a cubic equation with the tools giv...

Osvaldo SanchezF -1H

I don't know if it counts for anything but my T.A. said that there is not such a huge emphasis in sig figs this quarter and the processes are much more important so there is no need to stress about it as much like last quarter.

Osvaldo SanchezF -1H

Volume can also affect pressure when it increases as well. an increase in volume means that the concentration decreases so therefore the pressure decreases as well(P=(n/v*RT)). The reaction would not change however if the pressure was changed due to the presence of an inert gas that has no involveme...

Osvaldo SanchezF -1H

The magnitude of K does not change at a given temperature at equilibrium. K will be the same but you can start with different amount of product and reactant that will affect the direction that the reaction will favor so that it goes back to K at the specific temperature. But besides the initial amou...

Osvaldo SanchezF -1H

I want to assume that you refer to the problem when instead of having a quadratic we instead have a cubic equation. We have no way of solving for such an instance when the formula is a cubic one. So we will focus on what the change of the initial reactant will be. We will notice that the change is s...

Osvaldo SanchezF -1H

You can start to approach this by simply knowing that the addition of pOH and pH Is equal to 14 so (pOH+pH=14). So if you find the pH of the molecule using the molarity you found in each problem you can just subtract it to 14 and get pOH or vice versa.

Osvaldo SanchezF -1H

For ions, the basic rule is that a cation will always be an acid and a cation will be a base. To determine if molecules are a base or an acid, you can form an equation where it reacts with water and if it forms hydroxide then the molecule is a base but if it form hydronium then it is an acid.

Osvaldo SanchezF -1H

All. T.A.'s approach this differently and my T.A. said that if you miss a week you can make it up by posting more the next week. I would talk to your T.A. and see how they handle it. Some just check at the end of the quarter and see if you had 50 post in total.

Osvaldo SanchezF -1H

I would try to memorize as much as possible and after looking at it a couple times, most of it will be fairly easy to memorize because many are commonly used. As the previous person posted though, it is best to ask the T.A.

Osvaldo SanchezF -1H

To find the conjugate acid you just introduce a proton [H+] to a base and It becomes the conjugate acid of a base. And for a base, you remove a proton [H+] for an acid to form the conjugate base. That is why they are called conjugate acid/base pairs.

Osvaldo SanchezF -1H

You want the lewis structure to have the least amount of formal charges, or as close to 0. You don't want many atoms in the molecule to have a charge and want them to be as close to 0. So after considering this, you can deduce the shape that is created from the most favorable lewis structure.

Osvaldo SanchezF -1H

Both are considered bases but using reaction of the molecule with water solidifies why it is a base and anything with a hydroxide is a base.

Osvaldo SanchezF -1H

I don't believe that Lavelle has talked about this so I want to say that we will not have to know the exceptions and I believe that VSEPR to help determine shape is a golden rule and wont encounter a situation where will we need to know when not to apply it. I doubt Lavelle would want to trick us.

Osvaldo SanchezF -1H

I do not believe that Lavelle has mentioned anything about drawing hydrid orbitals so I doubt that we will have to draw anything about it.

Osvaldo SanchezF -1H

Dipole moments cancel each other in other forms besides being symmetrical which is one of the easiest way to identify this but only occurs when all the surrounding atoms are the same. But generally there has to be an even number of the same atom in a molecule for anything to even cancel out because ...

Osvaldo SanchezF -1H

The book on page 723 explains with detail when to use it but the simple matter of it, it that you use it when there is already prefix on the molecule name such as Di converts to Bi and etc, but I would take a glance at the reference number I gave you.

Osvaldo SanchezF -1H

If this does not change, just email your TA. The grading is based on how quick your TA grades them so if you are unsure it is always best just to email them.

Osvaldo SanchezF -1H

No the sigma and Pie bonds do not affect the molecular shape of a molecule, only the lone pairs do and the amount of bonds present. They do however affect whether certain atoms will be on the same plane. For example any atom connected to a double or triple bond will be in the same plane because pie ...

Osvaldo SanchezF -1H

The two lone pairs on Oxygen is what will make the shape bent, and because lone pairs are stronger than bonds it will be slightly less than 109.5.

Osvaldo SanchezF -1H

One way to make a distinction between the two is to know that Trigonal pyramid has 4 regions of electron density while, T-shape has 5 regions of electron density or 6 regions of density as it can be formed using 3 lone pairs and 3 atoms.

Osvaldo SanchezF -1H

I don't remember him mentioning it on the syllabus or in class so I do not think so. If anything a number like this should be given.

Osvaldo SanchezF -1H

To be sure it is best to use bent because that is what Lavelle said and he is the ultimate decider. They are the same thing though and at the end of the day is shouldn't matter but like I said to be safe just mention it as bent if that is what he refers it as.

Osvaldo SanchezF -1H

This type of inter-molecular force is the same thing as a Van der Wall force and can occur with any molecule and is the weakest form of inter-molecular force. Well an example for this is basically any molecule because even if it doesn't happen as often, there will be a point in time where two elemen...

Osvaldo SanchezF -1H

I got an email from my TA saying that you could turn it in if they had office hours before thanksgiving or during week 10. I do not know however if you have discussion before thanksgiving break though.

Osvaldo SanchezF -1H

Geometrically it would be referred as angular and the book mentions it this way. So as to not take any chances or confuse the grader I would stick with labeling it as angular. Also saying something is bent is very broad as you can say a shape of Trigonal Pyramidal is bent too.

Osvaldo SanchezF -1H

Basically anything below period 2 can have an expanded octet, due to their capability of being able to hold more electrons in their D-orbitals or F-orbitals. Hope this helps.

Osvaldo SanchezF -1H

When considering electron density, you only consider this for the central atom and not the outer ones. Each lone pair and bond whether single, double, or triple will be considered as a single electron density. It helps to determine the VSPER formula of AXE.

Osvaldo SanchezF -1H

You treat regions of electron density as bonds or lone pairs. For bonds however, no matter what type of bond it is, like double, single, or triple, they are considered one region of electron density. So just because there is a double bond, it doesn't mean that it has 2 regions of electron density.

Osvaldo SanchezF -1H

Yes Lavelle said that hybridization will not be in test #2. He mentioned this in class.

Osvaldo SanchezF -1H

For this the best approach is just study for it and memorize what bond angles goes with which shape. Personally if you know how to write the VSEPER formula of AXE for the molecules you can just remember that every molecule with the same formula will have the same shape and similiar bond angles.

Osvaldo SanchezF -1H

It is the strongest inter molecular force because it involves highly electronegative elements. Since hydrogen has only 1 electron and it forms bonds with high electronegative elements then the interaction is very strong due to those elements.

Osvaldo SanchezF -1H

There are many ways to determine whether a molecule is polar covalent or ionic. One method that is very practical is to see if the bond is between a non metal-non metal(covalent, possibly polar) or metal-non metal which is ionic. The difference in electronegative is a good way to determine this beca...

Osvaldo SanchezF -1H

For hydrogen bonds to occur, there must be a good overlap between the orbitals which is why many elements on row 2 can form good hydrogen bonds. However, Br is just too big, so the bond will be very poor since the overlap of orbitals between both elements is poor as well. Hydrogen bonds are strong d...

Osvaldo SanchezF -1H

Dipole moments usually occur when there is an unequal sharing of electrons and there is a positive charge with a negative charge on either end. For instances like this, the positioning of the atoms in the Lewis structure is very important.

Osvaldo SanchezF -1H

For every test that we get,we will always get a reference sheet with conversions and equations. This will be for all the test that we take for the class unless the conversion is so obvious then they won't give it but that is unlikely.

Osvaldo SanchezF -1H

When you draw lewis structures, they don't always have to have 0 formal charges and indeed it just depends on the molecule. The molecule itself could be positively charged or negatively charged and this means that for sure one of the atoms will have to be with a charge. When drawing the "best&q...

Osvaldo SanchezF -1H

Compared to covalent and ionic bonds, hydrogen bonds are the weakest because they are so easily broken just as it is easy to form them. So they are rarely fixed on one atom.

Osvaldo SanchezF -1H

Adding on to what the people have said, make sure the the element/atom with the highest electronegativity has a formal charge of (-) or the greatest negative charge because its the element that wants to attract electrons the most. ( this applies to a structure that had to have a (-) charge.

Osvaldo SanchezF -1H

it is not the element with the least ionization energy that goes in the middle, it is the element with the least electronegativity which is quite different. So based on that, you can now assume that the N should go in the middel because out of the elements given it is the one with the least electron...

Osvaldo SanchezF -1H

If it undergoes the same transition then it should be the same because well the same thing happened for both elements the only difference is the degree and extent to which it happened is different for each element.

Osvaldo SanchezF -1H

He said that the material covered will be everything we have learned up to Focus 2D.

Osvaldo SanchezF -1H

The best way to think about the problems such as this is to first how many electrons there are in the equations(valence electrons). Then put the element with the least electronegativity in the center and everything else in the outside. give everything an octet just by standard rule. After make sure ...

Osvaldo SanchezF -1H

From what I heard, the chemical structures with their name should be given as explained by some UA's and TA's.

Osvaldo SanchezF -1H

They are the exception because the elements in the 3 period can have a D-sub-shell so they can hold more electrons in the D- orbitals thus have an expanded octet if possible. However the elements in period 2 can go up to the 2p state and can only hold 8 electrons as anything in period 2 will have a ...

Osvaldo SanchezF -1H

I say to safe just stick to the equation that Lavelle gave. From what I heard though from some T.A. and U.A's, it is best to just use the short cut method so that you can focus on arranging the lewis structure in least charged state possible where(if need to) the atom with the highest electronegativ...

Osvaldo SanchezF -1H

Well a shell can be determined by the period on the periodic table. It tells you have many outer blocks of electrons it contains such as shell 1 contains 2 electrons and shell 2 contains 8 electrons. A sub shell is just the type of orbital where the electrons lie such as the S, P and D sub shells. T...

Osvaldo SanchezF -1H

My T.A. said that the exceptions have appeared in some test before, so it would be a good idea to know what the exceptions are and their configurations.

Osvaldo SanchezF -1H

If I am not wrong the most likely charge will be the result of how much electrons an element gains to fill its outer shell(in the example for non metals) and how much electrons an element loses to lose the few electrons that are present in its outer shell( most likely for metals) So for sulfur, it o...

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