CHEMISTRY COMMUNITY

Kathleen Vidanes 1E

When would we know to use Pt(s) vs. C(gr) in a galvanic cell?

Kathleen Vidanes 1E

Sorry! I meant 14.5 part d.

Kathleen Vidanes 1E

When writing cell diagrams, is there a certain order that the elements must be in within the anode side and within the cathode side?

Kathleen Vidanes 1E

Can someone please explain how to go about obtaining the half reactions for 14.5 part d please? Thank you!

Kathleen Vidanes 1E

For this problem, the deltaG obtained after adding reactions 2 and 3 was negative. However, when we divided it by the deltaG of reaction 1, it was written as a positive number. Why is there no negative sign? Is it because if the deltaG was negative, we would end up getting a negative number of moles?

Kathleen Vidanes 1E

The question reads:
"Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF, and heat:
What is the change in internal energy for the reaction of 1.00 mol OF2?"

How do you know that this is an ideal gas?

Kathleen Vidanes 1E

There was a homework problem that I did (15.53c) in which the 2nd step was the slow step, and it did contain an intermediate (NO3): Step1 NO2 + NO2 ⇌ NO + NO3 and its reverse (both fast, equilibrium) Step2 NO3 + CO --> NO2 + CO2 (slow) However, finding the rate law did not seem to be difficult: Rate...

Kathleen Vidanes 1E

Sometimes in a reaction mechanism, the 2nd step is the slow step, or rate-determining step. Does this have any significant effect on the overall reaction or the rate law, in contrast from having the 1st step as the slow step? If so, what effects are there?

Kathleen Vidanes 1E

Thank you so much for all of the help! I do prefer Beza’s method as well and believe that it much easier to understand, however I would also like to know how the solutions manual went about solving the problem. If anyone could explain, that would be great!

Kathleen Vidanes 1E

On page 620, Self-Test 15.3B reads: When the concentration of 2-bromo-2-methylpropane, C4H9Br, is doubled, the rate of the reaction C4H9Br(aq)+OH-(aq) --> C4H9OH(aq)+ Br- (aq) increases by a factor of 2. When both the C4H9Br and the OH- concentrations are doubled, the rate increase is the same, a fa...

Kathleen Vidanes 1E

Hi, I'm confused as to how we can find the order for B using experiments 2 and 3, especially since the initial concentration of A changes from 2.5 to 1.25. Could someone please explain how the order is found? Or if there is another method of determining the order for B? Thank you!

Kathleen Vidanes 1E

You have to fully calculate the kinetic law. This can only be done if you know all of the elementary reactions involved.

Kathleen Vidanes 1E

The question reads: In the reaction CH3Br(aq) OH (aq) S CH3OH(aq) Br (aq), when the OH concentration alone was doubled, the rate doubled; when the CH3Br concentration alone was increased by a factor of 1.2, the rate increased by a factor of 1.2. Write the rate law for the reaction. I'm still confuse...

Kathleen Vidanes 1E

For 15.3c, why is the rate of formation of NO not taken into account in the unique rate of the reaction? Is it because the value of the rate is the same, regardless of which species is indicated? Also, wouldn't we have to multiply the rate of reaction of NO2 by -1/2 since it is decreasing? The solut...

Kathleen Vidanes 1E

kaushalrao2H wrote:in general, remember that the rate constant k is dependent on temperature and the activation energy of the reaction.

Can someone please explain why that is?

Kathleen Vidanes 1E

I was confused about this, too. Wouldn't adding H+ ions indicate that the reaction is taking place in an acidic solution rather than a basic solution, though?

Kathleen Vidanes 1E

I just looked over my notes again and realized that if you wanted to go back even further with the derivation, you would have to know that deltaG = deltaG ° + RT ln ([P]/[R]) and deltaG = /nFE. From there, you can combine the two equations so that -nFE = deltaG ° + RT ln ([P]/[R]). Solving for E, yo...

Kathleen Vidanes 1E

Based on the example given during lecture (Will a gold ring dissolve in 1M nitric acid to form 1M Au3+ solution?),

Do we know that gold will not dissolve in 1M nitric acid solely because we end up with a positive deltaG°, meaning the reaction is unfavorable?

Kathleen Vidanes 1E

In class, to derive the Nernst Equation, we began with E= E° - (RT/nF) x ln Q. That equation can be rewritten in terms of logbase10 as E = E° - (2.303RT/nF) x logbase10 Q. At standard temperature (T=25°C or 298K), 2.303RT/F = 0.0592V, since R and F are both given constants. As a result, the Nernst E...

Kathleen Vidanes 1E

Why is it that if we want the equilibrium constant at two temperatures, we need to calculate the delta H(standard) and the delta S(standard)? Why can't we just use the equation delta G(standard) = -RTlnK and replace the T depending on the equilibrium constant that we are solving for?

Kathleen Vidanes 1E

We can assume that delta G is zero at equilibrium, because G(reactants)= G(products); At equilibrium, delta G = G(products) - G(reactants) = 0

Kathleen Vidanes 1E

You are correct in that you must use deltaG °rxn = -RTlnK and the free energy of formation of H2O. 1. Make sure that you are using the free energy of formation of water as a GAS / VAPOR (-228.57kJ/mol). 2. Multiple this number by 2, since there is a coefficient of 2 in the balanced chemical equation...

Kathleen Vidanes 1E

Hi, I am still a bit confused on the relationship between spontaneity and the direction of a reaction. For example, for 11.15, why is it that if delta G of the reaction is positive, that means the spontaneous reaction is proceeding towards the reactants? Does the rxn proceed towards the products if ...

Kathleen Vidanes 1E

No, I don’t think so. Dr. Lavelle just wanted to show us where the equations come from and how they relate to each other.

Kathleen Vidanes 1E

If a reaction is spontaneous, why does that imply that Delta G°of the reaction is positive?

Kathleen Vidanes 1E

How do we know when delta G°is equal to 0? What does this mean?

Kathleen Vidanes 1E

On homework question 8.77, why is it that the 6 C--H bonds within benzene are not added to the 3 C double bonds and the 3 C single bonds?

Kathleen Vidanes 1E

Although this might not necessarily relate to thermochemistry, I was wondering when do we know whether to specify H2O as being a liquid or vapor within a balanced chemical reaction, specifically for combustion? I was doing homework question 8.57 where we had to use Hess's law with multiple combustio...

Kathleen Vidanes 1E

Oh okay, thank you so much! That definitely helped. Follow up question, does that mean that the sum of multiple q's always equals 0? Or is that only when no energy is lost to the surroundings?

Kathleen Vidanes 1E

On the homework question 8.21, why is the heat lost by metal a positive value, while the heat gained by water is negative? Shouldn't a loss of heat be a negative value?

Kathleen Vidanes 1E

In discussion, we determined the initial temperature of a piece of copper that was dropped into water given the mass of Cu, volume of H2O, initial temperature of H2O, the specific heats, and final temperatures. The initial temperature turned out to be a much greater number that the final temperature...

Kathleen Vidanes 1E

It seems that many of the concepts throughout chapter 8 go back to the idea of state functions. I am still having trouble understanding the meaning of a state function as well as its relationship to enthalpy. Can someone please explain how enthalpy is a state function and why one can use the differe...

Kathleen Vidanes 1E

In my discussion, we did examples of phase change calculations where the number of moles of the substance and change in enthalpy (fusion and vaporization) were given. To calculate how much energy is needed for the phase change to happen, we used the equation: q=n x deltaH (fusion / vaporization). Do...

Kathleen Vidanes 1E

I am having trouble understanding why the temperature of a sample could remain constant even though heat is applied to it. Can someone please clarify this concept for me?

Kathleen Vidanes 1E

Steam burns more than liquid water, because more heat is supplied in order to turn the water into a vapor.

Kathleen Vidanes 1E

The heat capacity is the ratio of the heat supplied over the temperature rise produced (q/delta T),whereas the specific heat capacity is the heat capacity divided by the sample's mass (C/m). The heat capacity is an extensive property, because it depends on the size or extent of the sample. The speci...

Kathleen Vidanes 1E

Correct. Radicals are placed on the least electronegative atom, because the most electronegative atom would rather have a full octet. For example, on the very last midterm problem (HOCO), Carbon would get the radical because it is less electronegative than oxygen and oxygen would much rather have th...

Kathleen Vidanes 1E

For 11.89b, why are the partial pressures divided by 100?

Kathleen Vidanes 1E

Hi,

Can someone please explain how Cl2 is more stable just because it has a smaller equilibrium constant than F2?

Thank you!

Kathleen Vidanes 1E

Thank you so much! This helped a lot.

Kathleen Vidanes 1E

How do you determine whether a certain acid or base is considered weak or strong?

Kathleen Vidanes 1E

Are there any other molecules that are amphiprotic besides water? If so, what are they?

Kathleen Vidanes 1E

No,the K value for the reverse reaction would be the inverse of the forward reaction. Using the example given in class, if the K value for the forward reaction = 61.0, the K value for the reverse reaction will = 1/61.0 or 0.016

Kathleen Vidanes 1E

Hello, I have a question regarding the Lewis Dot Structure of N2H6. During my discussion section, my TA drew this so that both N's would each have one valence electron on them (radical). However, if I drew a double bond in between the two N's instead, would I be wrong? I calculated the formal charge...

Kathleen Vidanes 1E

I am having trouble understanding the reason as to why solids and liquids are not included in the K expression when solving for the equilibrium constant. Can someone please explain this in detail? Thank you.

Kathleen Vidanes 1E

Can someone please explain how EDTA has 6 bonding sites? Thank you.

Kathleen Vidanes 1E

I made a few mistakes on my Lewis Dot Structures on the midterm, because I did not draw them based on how they were written in the formula. For example, for HOCO, I did not draw it as H--O--C--O, but rather connected the hydrogen atom and the two oxygen atoms directly to carbon on three different si...

Kathleen Vidanes 1E

Carbon would form a triple bond with Nitrogen and a single bond with Chlorine in order to satisfy the formal charges for each atom in the Lewis Dot Structure. When it is drawn in this way and you calculate the formal charge for each atom, each one should have a formal charge of zero, which is what w...

Kathleen Vidanes 1E

So just to clarify, the least electronegative atom takes the radical electron because it does not need a full set as much as the more electronegative atom does? Is a "full set" considered a lone pair in this case, or a full octet?

Kathleen Vidanes 1E

Generally, lighter s- and p- block elements, like Beryllium (Be) and Boron (B) can have less than an octet. Elements that can have more than an octet include: Phosphorus (P), Sulfur (S), and Chlorine (Cl), and all elements that follow them. Depending on the formal charges that each one has once the ...

Kathleen Vidanes 1E

Phosphorus (P), Sulfur (S), and Chlorine (Cl) all have expanded octets. All of the elements following those three can have an expanded octet, as well.

Kathleen Vidanes 1E

When counting the regions of electron density in a Lewis Dot Structure, do we include lone pairs that are on the central atom?

Kathleen Vidanes 1E

How do we know that Beryllium has a lower ionization energy than Chlorine when they are not within the same period or group?

Kathleen Vidanes 1E

After drawing a Lewis Dot Structure, I am still confused as to how and why we write either a delta positive or delta negative next to each element. Can anyone please explain how this is done in full detail?

Kathleen Vidanes 1E

How do we know when to stop changing the numbers within the formula for formal charge in order to obtain the best representation of a certain molecule? For example, SO4^2-

Kathleen Vidanes 1E

Why is Sulfur allowed to have more than an octet in a Lewis dot structure? What other elements are allowed to have more than an octet and why?

Kathleen Vidanes 1E

Why is it that we use Px, Py, and/or Pz when writing the electron configuration for p-block elements,but not d-block elements?

Kathleen Vidanes 1E

After reading this, I am still a bit unsure of how the speed of light relates to velocity. Are they directly related / inversely related? Is speed of light (3.00x10^8m.s-1) interchangeable with velocity?

Kathleen Vidanes 1E

Why is it that when the electrons go down from a certain energy level due to the attraction to a positive cation, they do not go all the way down but instead end up at energy level one?

Kathleen Vidanes 1E

So, since the emission of electrons is not dependent on the level of intensity that the light is, will changing the wavelength effect its emission?

Kathleen Vidanes 1E

If given the grams of only one reactant within a question, should we automatically assume that that particular reactant is limiting?

Kathleen Vidanes 1E

If you are asked to find the empirical formula and are given a set of atoms along with their mass in grams, can you use those numbers to find the empirical formula without finding the mass percentage composition? Or do you always have to find the mass percent composition before finding the empirical...

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