CHEMISTRY COMMUNITY

Natalie LeRaybaud 1G

Do catalysts always appear on the left side of the reaction initially and then move to the right in the second step of the reaction?

Natalie LeRaybaud 1G

How can you tell what is being oxidized and reduced in this equation? And what is the cell diagram supposed to look like?
The problem is:

The following redox couple forms a galvanic cell which generates a current under standard conditions. O3/O2, OH- and O3,H+/O2

Natalie LeRaybaud 1G

Did anyone get this problem correct and know how to solve it?

Calculate the standard potential for the following reaction using the standard reduction potentials on the last page of the test:
(Cr2O7)^2- (aq) + 14H+ (aq) + 12e- --> 2Cr (s) + 7H20 (l)

Natalie LeRaybaud 1G

Q: What do dipoles say in passing?

A: Have you got a moment?

Natalie LeRaybaud 1G

I asked the guy sitting next to me if he had any Sodium Hypobromite...
He said Na BrO

Natalie LeRaybaud 1G

My TA said that it covers problems 1-39 in chapter 15

Natalie LeRaybaud 1G

I’m pretty sure you can be safe just memorizing them as Dr. Lavelle said we wouldn’t make sure derive anything one tests. However it is probably helpful just to know or go over how to integrate the rage laws.

Natalie LeRaybaud 1G

Yes it covers sections 15.1-15.6 which includes all the homework problems up till #39.

Natalie LeRaybaud 1G

Are the units of K constantly changing or are they always the same? And if they are changing, what are they according to each specific order?

Natalie LeRaybaud 1G

Yes I agree that it would have to be explicitly shown as [A]0 because otherwise it could be [A]t which refers to the final concentration at a certain time. So it is necessary to be able to differentiate between the 2.

Natalie LeRaybaud 1G

What is the main difference between a galvanic and electrolytic cell?

Natalie LeRaybaud 1G

I noticed that most of the solutions with cell diagrams from the homework include Pt(s) on one or both of the ends of the cell diagrams. Can someone please explain in which cases we add Platinum to the cell diagram and how we know whether it is on the anode side, cathode side, or both.

Natalie LeRaybaud 1G

Does anyone have a simple step by step method to forming and balancing half reactions because I always seem to get lost along the way.

Natalie LeRaybaud 1G

How does the calculation equation for work change when finding it depending on whether the reaction is reversible or not? Like when do you use -PdeltaV, and
-nRTlnv2/v1 ?

Natalie LeRaybaud 1G

Can someone please explain in what situations we multiply R by 3/2 and when we multiply it by 5/2. I mainly saw these calculations in internal energy problems but I am still quite confused on when they are specifically used.

Natalie LeRaybaud 1G

In what situations do you use Cv(vap) or Cp(vap) verses the normal specific heat capacities of water like the 4.184, 2.03, etc. values? This is referring to the context of calculating q in a heat curve problem, using q=mCdeltaT

Natalie LeRaybaud 1G

Yes there is a difference between a Galvanic cell and an Electrolytic cell. In a Galvanic cell the reaction proceeds without an external potential helping it along. Since you have the oxidation reaction at the anode, this produces electrons and thus a build-up of negative charge in the course of the...

Natalie LeRaybaud 1G

Can someone please explain how to go about doing this problem? Use the information in Table 8.3 to calculate the changes in entropy of the surroundings and of the system for (a) the vaporization of 1.00 mol CH4(l) at its normal boiling point; (b) the melting of 1.00 mol C2H5OH(s) at its normal melti...

Natalie LeRaybaud 1G

Can someone please explain the difference between irreversible and reversible expansion and the effect it has when calculating entropy? I saw the diagrams of each posted on the website but now I feel a bit more confused on the subject.

Natalie LeRaybaud 1G

In addition, molecules that are considered more complex tend to have greater entropies. Since CoF2 can be arrange in more different orientations when compared to BF3, it is considered more complex and this has a greater entropy.

Natalie LeRaybaud 1G

Generally it is based off the information given within the problem. For instance if the temperature and amount of moles or mass of substance is given with aa changing volume, it is probably best to use the 2nd equation. If you are given a constant value of pressure then it would be safe to use the f...

Natalie LeRaybaud 1G

Yes, heat and work (q and w) are not considered state functions because they are dependent on the path taken whereas E, P, V, T, densities, and heat capacity as well as the ones we just learned deltaU, deltaH, deltaG, deltaS are all state functions.

Natalie LeRaybaud 1G

Yes you would always use these temperature intervals because according to the heat curve 0 degrees is waters melting point and 100 degrees is the boiling point for water. These temperatures are significant because it is right at the point before a phase change occurs. Ex: 0 degrees: solid-> liquid a...

Natalie LeRaybaud 1G

Not always. Sometimes there are other factors present in a system to take into account that can have an impact on the overall energy. However, when there is a direct heat transfer such as in this case the Copper transferring heat to the water, then the sum of the qs in the system equals zero.

Natalie LeRaybaud 1G

After going through the homework I noticed numbers 3-13,25-31, and 47-49 all have to do with calculating work or internal energy. I would suggest studying all the other homework problems specifically for this upcoming test.

Natalie LeRaybaud 1G

Although it isn't explicitly listed on the syllabus, I would still suggest making sure you know it because it will come in handy when doing problems in the future and its always good to have background knowledge with these things.

Natalie LeRaybaud 1G

When calculating the enthalpy using bond energies do we multiply the bond energy by the amount of moles the molecule has within the reaction or by the amount of bonds in the molecule? For example in number 75 the solution manual did not multiply the C-H bond energy by 4 even though the initial equat...

Natalie LeRaybaud 1G

Can someone please explain how to go about doing this problem? Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the mean bond enthalpies in Table 8.7 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of b...

Natalie LeRaybaud 1G

Extensive: depends on the amount of matter present Intensive: does not depend on the amount of matter in a substance It is important to know the properties because since all things are made up of matter it is necessary to understand these characteristics for calculations and whether or not a chemica...

Natalie LeRaybaud 1G

A coffee cup calorimeter is good for measuring heat flow in a solution however it can’t be used for gaseous reactions because the gas would escape from the styrofoam cup. Although they both have the same function, the bomb calorimeter is generally used to measure heat flows for higher temperature re...

Natalie LeRaybaud 1G

The exothermic phase changes are the ones that occur going down a heat curve. This is because they are releasing energy during the reaction and therefore have energy as a product and have a negative delta H (enthalpy). This includes freezing, condensation, and deposition as stated above.

Natalie LeRaybaud 1G

How does compressing a system affect the overall reaction? This includes in matters such as volume, concentration , equilibrium, etc.

Natalie LeRaybaud 1G

How do you know when and how to simplify cubic equations when solving an ICE box problem?

Natalie LeRaybaud 1G

I just noticed the following problem involves a quartic function. Are we supposed to expect quartic functions with ice boxes on the final? If so can someone please explain how to solve this problem? I have tried various times and the solution manual does not show the steps in solving for x. A reacto...

Natalie LeRaybaud 1G

Is there any way to assume X to be too small without calculating the actual value of X and using the 5% rule?

Natalie LeRaybaud 1G

Yes I agree. The best way is to use stoichiometry to find how many moles of a certain product the reaction will yield based off of the initial amount of reactant you are given in the problem. The reactant that yields less moles of product is the limiting reagent.

Natalie LeRaybaud 1G

Can some one please explain part B to this problem? Benzyne, C6H4, is a highly reactive molecule that is detected only at low temperatures. It is related to benzene in that it has a six-membered ring of carbon atoms; but, instead of three double bonds, the structure is normally drawn with two double...

Natalie LeRaybaud 1G

Can someone please explain how to solve this question, using the quadratic formula? A reaction mixture is prepared by mixing 0.100 mol SO2, 0.200 mol NO2, 0.100 mol NO, and 0.150 mol SO3 in a 5.00-L reaction vessel. The reaction SO2(g) NO2(g) ∆ NO(g) SO3(g) is allowed to reach equilibrium at 460 C, ...

Natalie LeRaybaud 1G

A quick way to determine hybridization is to look at the electron domains. Generally if a molecule has less than 5 electron domains, the hybridization has the number 1 less than the amount of domains. For example 4 e- domains: SP3, 3 e- domains: SP2, 2 e- domains: SP. Thats just a quick way to check...

Natalie LeRaybaud 1G

Another way to quickly determine whether a molecule is polar or non-polar is to look at the lewis structures. Generally, a non-polar molecule will look completely symmetrical, such as CCl4. The chlorines pull on the carbon in an equal manor with equal bond angles. Other lewis structures which are no...

Natalie LeRaybaud 1G

In general you would put the lone pairs on the central atom, unless of course it follows the octet rule and can not have more than 8 valence electrons bonded. But overall pay attention to the octet rule and if the central atom follows it, then the lone pair is most likely to be placed on the central...

Natalie LeRaybaud 1G

Do lone pairs effect hybridization? And if so what would be the hybridization of an atom with more than 4 or 5 electron domains ?

Natalie LeRaybaud 1G

No I don't think that you will have to know pi bonds for the midterm.

Natalie LeRaybaud 1G

I'm pretty sure it is Reaction Coefficients.

Natalie LeRaybaud 1G

No I remember in class that he said that as long as you got the electron distribution right and the relative shape, it would be fine. He also said that either _I_ or the Mercedes logo shape would be fine specifically for trigonal planar structures.

Natalie LeRaybaud 1G

Yes you can assume this only if you have solved for the amount after your conversions. Like after you convert from percent-->grams-->moles--> and then divide by the smallest mole. The lowest value at that point is safe to say is the limiting reactant, otherwise you can't assume (like if your just ta...

Natalie LeRaybaud 1G

How can you determine if an atom is in its ground state or excited state just by looking at the electron configuration?

Natalie LeRaybaud 1G

Can someone please explain why Oxygen is an exception to the ionization energy trend of the periodic table, like when it is compared to Nitrogen or Fluorine?

Natalie LeRaybaud 1G

Are we always supposed to put the 4s orbitals after the 3d? Because in high school I'm pretty sure we learned to write out 4s then 3d. For example the electron configuration for Gallium I thought would be Ga: [Ar] 4s2 3d10 4p1 but are we now supposed to write it as Ga: [Ar] 3d10 4s2 4p1 ? And if so ...

Natalie LeRaybaud 1G

Do we always have to separate the p orbitals? For example like px, py, pz? And if so, why is it only done for p orbitals?

Natalie LeRaybaud 1G

Honestly, it doesn't really matter. You will get the correct answer either way. But it would be safer to be more exact so I would suggest using 2.998*10^8. Just remember to round to the nearest Sig Fig.

Natalie LeRaybaud 1G

Yes, I agree my TA specified to know the Electromagnetic Spectrum, not in the sense that you need to memorize every single value but like if you were to be given a specific wavelength, you should be able to estimate which area its in. Visible Light will be the most common.

Natalie LeRaybaud 1G

Yeah I agree. You mainly want to round when you get a number ending in like .5, .333, .666. etc. Other then that, if the number is below .5 in the tens place then round down and if above, round up.

Natalie LeRaybaud 1G

So a little trick to remember sig figs is the PACIFIC/ATLANTIC rule. If the decimal is PRESENT you start from the left side (Pacific) and go to the first non-zero number and count that one as well all the numbers after Ex: 0.004670 would be 4 sig figs because the 1st non-zero number is 4 so you coun...

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