CHEMISTRY COMMUNITY

ckilkeary 2G

For problem 6L 9. in the chemistry textbook (particularly part a), it wants you to write the balanced half reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride. I understand how in the half reactions we get Fe 2+ and MnO4 - because those are the ...

ckilkeary 2G

(for reference this is problem 6L 7 part c in the textbook) When given the reaction in the nickel-cadmium cell which is: Cd(s) + 2 Ni(OH)3 (s) -----> Cd(OH)2 (s) + 2 Ni(OH)2 (s) and asked to write the cell diagram, the textbook gives the answer: Cd(s) | Cd(OH)2 (s) | KOH (aq) || Ni(OH)3 (s) | Ni(OH)...

ckilkeary 2G

If given the reaction (and told its a Bronsted neutralization reaction): H+ (aq) + OH- (aq) ----> H2O (l) and told to write the half reactions in the anode and cathode the textbook gives the answers: anode: 4OH- (aq) -----> O2 (g) + H2O (l) + 4e- cathode: O2 (g) + 4H+ (aq) + 4e- ----> 2 H2O (l) How ...

ckilkeary 2G

This part of the question wants you to write the half reactions for the given skeletal equation of Au^+ (aq) --> Au (s) + Au^3+ (aq)

How do you figure out how to write the half reactions and overall balanced equations for this skeletal equation?

ckilkeary 2G

In this problem, the galvanic cell given is
Cu (s) | Cu^2+ (aq) || Ce^4+ (aq) , Ce^3+ (aq) | Pt(s)

My question is: is there a reason that they separated Ce^4+ and Ce^3+ with a comma instead of the "|" like in other problems?

ckilkeary 2G

Came across this question of writing half-reactions and the overall balanced reaction for galvanic cells. Part b) wants you to write these for C(gr) | H2 (g) | H+ (aq) || Cl- (aq) | Cl2 (g) | Pt (s) In the solutions, we don't include C and Pt for the half reactions or overall reactions. Why is that ...

ckilkeary 2G

Could someone explain how to write the half reactions for the reaction of ozone with bromide ions:

O3(aq) + Br^1 (aq) ---> O2(g) + BrO3^- (aq)

ckilkeary 2G

The part of this I'm getting stuck on is the oxidation half-reaction. Could someone explain how they got the oxidation half-reaction step by step of
Cl2 + S2O3 ^2- --> Cl^- + SO4

ckilkeary 2G

This question is: 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) ---> Cr^3+ (aq) + C2H4O(aq) + H2O(l) (d) Combine the half-reactions to produce a balanced redox equation Now, I got the...

ckilkeary 2G

So I tried to do the question 5J 15. which is as follows: Calculate the equilibrium constant at 25C and at 150C for each of the following reactions, using data available in appendix 2A: NH4Cl(s)<->NH3(g)+HCl(g) However I got the wrong answer so if someone could look over this and tell me where I wen...

ckilkeary 2G

For this one I converted Torr to atm ( 1 Torr=0.001316 atm ). Then I converted mL to L. Then you can convert L*atm to J using the conversion ( 1 L*atm=101.325 J ).

ckilkeary 2G

Quick clarifying question: what is the difference between getting a negative value for w vs a positive value? for example, what is the difference between w=20J vs w=-20J?

ckilkeary 2G

For part a) you should use the equation q=m*Cs*ΔT to find the heat needed to change the temperature of the copper to 100 degrees Celsius (for Cs use the table in the textbook for the table that gives the specific heat capacity of copper). Then do the same thing to find the heat it took to raise the ...

ckilkeary 2G

For this problem, it is stated that the internal energy of a system increased by 982 J when supplied with 492 J of energy as heat. I'm confused about part b). Part b) asks how much work was done. Originally I thought that this was a simple calculation using ΔU=q+w so I plugged in 982 J for ΔU and 49...

ckilkeary 2G

Here's the full problem: Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (a) How much work is done in the compression? (b) Is the work positive or negative with respect to the air in ...

ckilkeary 2G

How do we find deltaV when figuring out this problem? I'm not sure how to get deltaV from knowing that the inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm. I'm trying to get deltaV so I can plug it into w=Pex*deltaV

ckilkeary 2G

This question states that air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (a) How much work is done in the compression? (b) Is the work positive or negative with respect to the air in...

ckilkeary 2G

I think I have a pretty good understanding of the different types of thermodynamic systems, but could someone explain exactly what a bomb calorimeter (in which benzene is burnt) is and how it is an isolated system?

ckilkeary 2G

Solids and liquids don't appear in the K expression because the atoms in solids and liquids are so close together that they don't have much room to squeeze any closer together. It would take a super huge immense amount of force to push these atoms any closer together and cause a change in volume. So...

ckilkeary 2G

I know that so far in lectures we have used this formula to convert between partial pressure and concentration. Other than that I don't think we've been given more reasons to use the formula.

ckilkeary 2G

When a reaction is at equilibrium, I think it means that the rate at which products and reactants are being formed is constant rather than equal. Basically meaning that if the forward and reverse reactions are both happening, it doesn't change the amount of products and reactants to cause a change i...

ckilkeary 2G

The only difference between the two is that Q is a term used when it hasn't reached equilibrium yet. Since they're solved the same way, Q and K are just different terms you use depending on the situation.

ckilkeary 2G

I know that when writing K and Q expressions you don't include molecules in solid and liquid state. But what about aqueous?

ckilkeary 2G

As a follow up question, what are the general rules for determining the strengths of bases? For acids, it's through bond length and electronegativity, but I don't think Lavelle explicitly mentioned the criteria for bases. Thanks! I had the same question and did a little bit of research online and f...

ckilkeary 2G

When naming [Fe(CN)6] 4- , why is the name in the answer key hexacyanoferrate (II) ion? Specifically as opposed to what I thought it would be: hexacyanidoferrate (II) ion.

ckilkeary 2G

I just really don't understand the book explaining what a chelate is. Anyone here that can explain it better or just in different words?

ckilkeary 2G

In the molecule Ferrocene (and likewise "sandwich compounds") is there a bond between connecting the central atom, Fe, with another atom? In the diagram in the book I can't really see any bonds coming off it so I don't know how the planar ligands are being held together.

ckilkeary 2G

The book says that in some cases the order of ligands in the name is not the same as the order in the formula. How would we know if that's the case?

ckilkeary 2G

When writing the formula in the steps to name a compound, how do you know what to put in brackets and include in the coordination sphere?

ckilkeary 2G

I understand what a substitution reaction is (where one Lewis base takes the place of another) but how and why would this occur if there's already a Lewis base connected?

ckilkeary 2G

Molecular geometry is how the lone pair(s) and bond pair(s) are arranged around the central atom and the shape is the molecular structure that doesn't include the lone pair(s) on the central atom.

ckilkeary 2G

Nonpolar means that the dipole moments cancel out. In the case of CO2, because the oxygens (one each side) have the same strength of "pull" and effectively cancel each other out. Think of if as if there were two of the same person pulling at each side in tug of war. The rope in that game w...

ckilkeary 2G

In the hydromium ion, there is one lone pair on the oxygen and three bonds (one for each H). You misinterpreted the shape as T-shaped. T-shaped would be more if there were two lone pairs on the oxygen instead of one. Instead the shape is trigonal pyramidal. It looks like one lone pair on top repelli...

ckilkeary 2G

In the case of AX2E3, there are 3 lone pairs and with the strongest repulsion being lone pair-lone pair, these lone pairs are spaced out on the same plane as far away from each other as possible being at about 120 degrees away from each other. Then adding in the two bonds to the central atom, the pu...

ckilkeary 2G

Each bond, whether single or multiple, just acts together as a single unit of high electron concentration repelling other bonds or lone pairs. Because of this, in our VSEPR model we treat all the types of bonds the same in counting regions of electron concentration.

ckilkeary 2G

How I think it works are larger atoms and molecules have stronger attractive interactions because valence electrons are farther from the nuclei so they are less tightly held to the nucleus and can form dipoles with more ease.

ckilkeary 2G

I know Lavelle said something in class about this but I wasn't fast enough to write it down. So in terms of the Interaction potential energy equation that he gave us (the one that has the divided by r^6), why is the potential energy always negative?

ckilkeary 2G

In the book (for reference on page 96) they gave two ways that a dipole is represented. They said that in the original convention the dipole was represented by an arrow pointing to the negative dipole charge. However they said more modernly the arrow points to the positive charge. Which convention d...

ckilkeary 2G

To my understanding, dissolving in water has to do with the positive part of water molecules attracting the more negative parts of a molecule and the negative part of water molecules attracting the positive parts of the same molecule. If you have a higher difference in electronegativity (therefore h...

ckilkeary 2G

When we're asked to draw a Lewis Structure on the Midterm tomorrow, do we have to draw all of the resonance structures for full credit or can we just draw the one? ie for CO32- should we draw three Lewis structures with each having a double bond on a different O attached to the C or should we just h...

ckilkeary 2G

This problem was in the Dino Nuggets Review particularly problem 10c) Which has a higher electron affinity, Chlorine (Cl) or Neon (Ne)? The answer was Cl although this the trend for electron affinity on the periodic table I thought was that electron affinity increased going to the right of the perio...

ckilkeary 2G

does 3d have higher energy than 4s? can someone explain why/why not? Thanks! The 4s level is lower in energy when there are no electrons in the 3d level (hence why the 4s level is filled first), but once that 3d level gains an electron, it becomes the lower level and is therefore put first in the e...

ckilkeary 2G

The 4s is only lower in energy when there are no electrons in the 3d level. However as soon as the 3d level gains an electron, the 4s ends up higher in energy. I think its a pretty complex reason exactly why when we add an electron into 3d that the energy levels fluctuate (I think the book said from...

ckilkeary 2G

I can give you an example of the Schrodinger equation that we did in a review session today. Ex. Beta-carotene is a conjugated polyene with delocalized electrons. This system can be treated as a particule in a box. If H= (h/8Π^2m)((d^2)/dx^2) write the schrodinger equation for this system. We used t...

ckilkeary 2G

Well the rules for electron configurations are Aufbau's Principle, Pauli-exclusion principle, and Hund's Rule. Aufbau says that we have to build our energy levels from the bottom level. Pauli says that there cannot be more than 2 electrons per orbital and that if there are two they must be spin pair...

ckilkeary 2G

We know that these are ions that have had two electrons taken away because their charge is 2+. So we can add those ions back to the electron configuration, but we have to keep in mind that the two electrons were likely taken from the 4s subshell since 4s has to be filled before we start adding to th...

ckilkeary 2G

During the "Dino Nuggets" review session on Friday, we went over the problem 12b) Draw the lowest energy Lewis structure for ClO4- We started by giving Cl (the central atom in this case) a bond for each oxygen it was connected to, but then to lower the formal charge of the structure, start...

ckilkeary 2G

The goal is to limit the formal charge overall for the molecule to find out which atom arrangement suits the molecule best.

ckilkeary 2G

For 2B.3 part d, can someone explain how the central atom Br of BrF3 has three bonds as well as 2 pairs of lone electrons? (seemingly like 10 electrons) As well as why one of the F atoms only has one bond and 2 pairs of alone electrons? (seemingly like 6 electrons) I don't know if I'm reading it wro...

ckilkeary 2G

Yes, exactly. The more electrons added to the outer shell the more electrons far away from the nucleus and the atomic radii increases.

ckilkeary 2G

Yes, exactly. The more electrons added to the outer shell the more electrons far away from the nucleus and the atomic radii increases.

ckilkeary 2G

The ionization energy is the energy it takes to remove an electron from an atom. Ionization energies are paired with atomic radius. Since atomic radius increases from left to right on the periodic table so does ionization energy. Na is to the left of Mg so this would mean that Na has the smaller ato...

ckilkeary 2G

How do we know that bromine gets 10 valence electrons? Bromine actually only has 7 valence electrons. An easy way to tell this is because Bromine is one column to the left of the noble gases that all have a complete set of 8 electrons on their outer shell. Sharing with the three Fluorine atoms lets ...

ckilkeary 2G

Black body radiation is what is emitted at different wavelengths by an object heated for a series of temperatures that does not prefer one wavelength over another in terms of absorption. The only time we really mentioned black body in lecture was to say that the description of light as photons expla...

ckilkeary 2G

You use Wien's law when you need to find temperature given a maximum wavelength of radiation or when you need to find a maximum wavelength when given the temperature. If they mention max wavelength of anything and want you to find the temperature that's when you use Wien's law, and I don't think you...

ckilkeary 2G

A diffraction pattern comes from when the highs and lows of waves hit the highs and lows of other waves going a different direction. Diffraction patterns are important to what we're studying because they help prove that electromagnetic radiation is wavelike. Its modeled in the double slit experiment...

ckilkeary 2G

I like to think of Lavelle's example of a baseball going through a stream of photons vs an electron. A baseball is large and we can see the definite trajectory that it is going. Photons aren't going to alter this trajectory in any way because their size just doesn't even begin to compare to a baseba...

ckilkeary 2G

If I remember correctly, when we did that equation and calculated the velocity based on if the electrons could be in the nucleus we found that it said the velocity of electrons would be faster than the speed of light because they were faster than 3×10^8 ms-¹. However that's simply not possible and e...

ckilkeary 2G

We briefly mentioned it as one of the three fundamental equations from this section. But it is in the book and we will probably end up going over it. For future reference it is Δp * Δx ≥ (1/2)ћ Δp is uncertainty in momentum Δx is uncertainty in position ћ (pronounced "h bar") means h/2(pi)...

ckilkeary 2G

It is possible that you can be given the amount of a product and asked to find the amount of each of the reactants needed to make that much product. If you're given the product in grams you can convert them to moles and use the molar ratio between that given product and the reactant they're asking y...

ckilkeary 2G

Since E = hv, we know that energy is directly proportional to frequency. We also know that λ x v = c (with λ being wavelength). If we rearrange the equation we get v = c/λ. By combining that with our energy equation we get E = h * (c/λ) = (hc/λ) So from this we see that Energy is indirectly proporti...

ckilkeary 2G

The Balmer series contains the visible part of the light spectrum, whereas the Lyman series is in the ultraviolet range on the light spectrum.

ckilkeary 2G

The intensity is the square of the amplitude. So it is determined by the height of the wave. The frequency has to do with the wavelength and the number of oscillations. A long wavelength means fewer oscillations and low frequency.

ckilkeary 2G

If someone could be kind enough to explain the observations from the photoelectric effect in as close to layman's terms it can get, it would be really great. Thank you!

ckilkeary 2G

The book says "White light is a mixture of all wavelengths of visible light". So does this mean that on the visible light spectrum it has no specific place? Or that it doesn't have a specific frequency or wavelength? I wonder if there's any way to define it like that or get clarification o...

ckilkeary 2G

When talking about the speed of light the unit used is m/s^-1. If the s stands for per second, why is there an exponent of -1?

ckilkeary 2G

Well the atomic spectra is a collection of the specific and various wavelengths of light emitted by atoms. Often observed through spectroscopy.

ckilkeary 2G

I know that the unit of frequency when looking at the oscillation of an electromagnetic wave is called a hertz. However, is there a unit for when looking at the amplitude/height of the wave?

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