CHEMISTRY COMMUNITY

Kaylin Krahn 1I

if it is seen in the overall reactant and also in the products therefore "cancelling out" and not being consumed

Kaylin Krahn 1I

Are we supposed to know that average kinetic energy is equal to (3/2)RT? Overall, how does the solution manual obtain these answers and are we expected to know this formula even though it's not given on the sheet?

Kaylin Krahn 1I

Conceptually, how does delta G = work max = -nFE ?

Kaylin Krahn 1I

No, that did not indicate that the second step was the slow step. You have to test it. I think he did that just to have us go through a little more work because if the first step was the slow step, it would have been an easier, shorter problem.

Kaylin Krahn 1I

If your half life is 6 days, in 30 days you will go through 5 half lives.

If you start with 100% you divide it by 2 (or multiply by 1/2) five times to get 3.1%
100/2=50% 1 half life
50/2=25% 2 half lives
25/2=12% 3 half lives
12/2=6.25% 4 half lives
6.25/2=3.125% 5 half lives

Kaylin Krahn 1I

If it is produced in a step and a product in another, therefore being cancelled out of the overall reaction, then it is an intermediate

Kaylin Krahn 1I

Why does unique rate use stoichiometric coefficients and the other equations do not need coefficients?

Kaylin Krahn 1I

.693 and my response is actually for a first order half life equation. t(1/2)= (ln2)/k

second order half life is t(1/2)=1/(k[A]0)

Kaylin Krahn 1I

second order half life numerator is always ln 2 because it is not dependent on initial concentration so .693 is just ln 2

Kaylin Krahn 1I

Reactions that are initiated by mixing the reagents can be studied by the stopped-flow technique, in which solutions of the reactants are forced into a mixing chamber very rapidly and, within a few milliseconds, the formation of products is observed spectroscopically. This procedure is commonly use...

Kaylin Krahn 1I

What is the stopped flow technique and what is it's relation to kinetics?

Kaylin Krahn 1I

What exactly is a pseudo order reaction? Do we need to know this?

Kaylin Krahn 1I

Why is it that in part b, the solution manual says that E cell not and E cell are both temperature dependent? Shouldn't E cell not only be at 25 degrees Celsius? How is it temperature dependent then?

Kaylin Krahn 1I

it is thermally insulated. heat does not enter or leave the system

Kaylin Krahn 1I

ΔG° is Gibbs free energy at standard conditions. You use ΔG° to find ΔG by ΔG=ΔG°+ RTlnQ

Kaylin Krahn 1I

When dealing with an ideal gas and if you are looking for one of the variables and given the others. You're not really directed to use it, but you use it to find a missing variable that you might need. For example, if you need to use volume but you're given moles, temperature, and pressure. Also, wo...

Kaylin Krahn 1I

If work is done by the system, -w, it means expansion. If work is done onto the system, +w, it means compression.

Kaylin Krahn 1I

Also, if there are two changes in a combination of temperature, pressure, and volume, you would add the two steps together to get combined entropy change. In a review session, an example was entropy change of 2.00 mol of Argon gas volume from 10L to 5L and Temperature from 300K to 100K with Cv= 12.4...

Kaylin Krahn 1I

Cv is specific heat in constant volume and Cp is specific heat in constant pressure. So when you are calculating entropy change with a change in temperature and constant volume, you would use the equation delta s = nCvln(T2/T1). If you are calculating entropy change with a change in temperature and ...

Kaylin Krahn 1I

Why is it that the compounds with a positive free energy of formation are unstable with respect to the elements?

Kaylin Krahn 1I

You can change an extensive property to intensive by dividing it by something like mass so that it is not "dependent" anymore

Kaylin Krahn 1I

Yes the third law states that the limit of t approaching 0K of S will be equal to 0 for perfect monatomic crystals

Kaylin Krahn 1I

End of Sunday

Kaylin Krahn 1I

You use bond enthalpies to find the enthalpy of formation by subtracting the sum of the bond enthalpies of formed bonds from the sum of the bond enthalpies of the broken bonds.

H=sum of broken - sum of formed

Kaylin Krahn 1I

I think the book tends to denote enthalpy as kJ/mole of the reaction given, which does not mean necessarily per mole of the molecule. I believe my TA said that Dr. Lavelle usually doesn't write it this way in lecture as it can be confusing, but I believe the book just means kJ per mole of the reacti...

Kaylin Krahn 1I

The bomb calorimeter is isolated because it does not allow exchange of heat or matter, but the coffee cup calorimeter has to be open to have constant pressure.

Kaylin Krahn 1I

I would consider the ideal gas law PV=nRT because you are changing the number of moles which may change another variable, which would affect the energy of the system.

Kaylin Krahn 1I

How did the solutions manual go from -(1.00atm)(1.20L) to -122J?

Kaylin Krahn 1I

The work is positive because the work was done onto the system instead of by the system.

Kaylin Krahn 1I

Can someone walk me through how to do this problem? (Use tables 8.3, 8.6, 8.7) Estimate the enthalpy of formation of each of the following compounds in the LIQUID state. (standard enthalpy of carbon sublimation is 717 kj/mol) a) H2O b) methanol, CH3OH c) benzene, C6H6 (without resonance) d) benzene,...

Kaylin Krahn 1I

For most equations we assume the temp is 25 degrees celsius, which is equivalent to 298K, so I think it was just assumed the equation took place at standard temperature since a temperature wasn't given.

Kaylin Krahn 1I

So you know the first equation is multiplied by 2 to get 2HBr, the second equation is reversed, and the third is left alone. If you write these out, it's easy to see which parts cancel. 2NH3, 2NH4Br, and N2 cancel leaving you with the desired H2+B2+2HBr. Remember to respectively change the delta H t...

Kaylin Krahn 1I

It would but in a two-step process. The first equation would yield HSO4- and the second would have HSO4- as the acid and yield SO4(2-)

Kaylin Krahn 1I

It's an equilibrium constant at specifically 25 degrees celsius. Since it's a constant it's always the same number at this temperature.

Kaylin Krahn 1I

Give the Ka value for the acids
part d, HSeO4- pKa2=1.92
would you just solve for Ka2? Can you solve for Ka1? In the solution manual it has the answer for Ka2 but it is labeled Ka1? Or am I seeing it wrong?

Kaylin Krahn 1I

Lewis acid: electron pair acceptor
Lewis base: electron pair donor
Bronsted acid: proton donor
Bronsted base: proton acceptor

(focus is just different!)

Kaylin Krahn 1I

Does it matter if you write H2O or OH2 when writing the coordination compound if it has "aqua" in the name?

Kaylin Krahn 1I

A 25.0-g sample of ammonium carbamate, NH4(NH2CO2) was placed in an evacuated 0.250-L flask and kept at 25 degrees C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The rxn is NH4(NH2CO2) (s) <--> 2NH3 ...

Kaylin Krahn 1I

You are just supposed to understand that if you have molecules with lone pairs, it will "push" the other atoms to create an angle slightly less than what would usually be expected

Kaylin Krahn 1I

A limiting reactant is the reactant in an equation that determines how much product will be produced. This is found by determining how many moles of each reactant you have and comparing it to the ratio of reactants found when balancing the chemical equation. Theoretical yield is the maximum potentia...

Kaylin Krahn 1I

No one responded to me so I'm posting this question again

Is the solution manual indicating the shape of the molecule? Why is it drawn this way?

Kaylin Krahn 1I

CO can be linear and have a dipole moment because it is not cancelling out. The oxygen will "pull" on the carbon creating a dipole moment. In comparison, CO2 does not have a dipole moment because it is linear and the bond dipoles cancel each other out.

Kaylin Krahn 1I

Chem_Mod wrote:Hi Kaylin,

Would you mind including a photo of said question and corresponding answer?

Thanks!

Kaylin Krahn 1I

Is the solution manual indicating the shape of the molecule? Why is it drawn this way?

Kaylin Krahn 1I

Why wouldn't ClO2 have double bonds instead of single bonds? (The solution manual shows the answer with single bonds)

Kaylin Krahn 1I

In 3.61 for example, how do you know where to put the extra electrons? Iodine gets more lone pairs added instead of bonding more. Do you just try different structures and test for the lowest formal charge?

Kaylin Krahn 1I

The central atom tends to be the one with lower ionization energy or the least electronegativity, so you would have to know the trends of the periodic table.

Kaylin Krahn 1I

The atom with the least electronegativity or the lowest ionization energy tends to be the central atom.

Kaylin Krahn 1I

How do you determine how many unpaired electrons an atom has? I understand the Aufbau principle and Hund's rule, so I'm wondering if you have to write out the electron configuration to figure this out or if there's an easier way?

Kaylin Krahn 1I

Very simply, as the number of protons increase, the added valence electrons will be pulled toward the nucleus more, which makes the radius smaller. So as you move right on the periodic table, more protons and electrons = greater attraction and smaller radius

Kaylin Krahn 1I

Uncertainty is not on this test. It will cover up to de Broglie but you can read ahead to prepare for what's coming up since it is in the chapter.

Kaylin Krahn 1I

It does the same exact thing. Dr. Lavelle said he doesn't prefer the equation in the book because students were getting confused on which place to put the final and initial energy levels whereas the delta E equation is more clear and straight forward AND tells you which direction the energy is going...

Kaylin Krahn 1I

It describes how light has wavelike properties. In problems it is used when given momentum, mass, velocity, wavelength since those are the variables. You would not cross over this equation with the others though because that's about light as particles or photons.

Kaylin Krahn 1I

moles of Carbon = (2.1x10^9 atoms)/(6.0221415 × 10^23 mol^-1) = 3.5x10^-15 mol C

divide by Avogadro's number because it refers to how many atoms are in one mole

Kaylin Krahn 1I

You would first find the limiting reactant and then use the ratio from the balanced chemical equation to find how much of the excess will be used. Then subtract how much will be used by the total excess... So if you have two moles of each reactant and the ratio is 1:2, the amount of excess used is 1...

Kaylin Krahn 1I

^I believe that was the molecular and empirical formula since we were also given the molar mass

Kaylin Krahn 1I

The question: Practitioners of the branch of alternative medicine known as homeopathy claim that very dilute solutions of substances can have an effect. Is the claim plausible? To explore this question, suppose that you prepare a solution of a supposedly active substance, X, with a molarity of 0.10 ...

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