CHEMISTRY COMMUNITY

Haley Dveirin 1E

Here's a couple more differences:
- T is constant in a reversible pathway but changes along an irreversible pathway
- V increases and P decreases during a reversible run but for irreversible work is done against a constant P
- more work is done in a reversible reaction than irreversible

Haley Dveirin 1E

i'm not 100% sure why but I think it has to do with that option being the most concentrated.

Haley Dveirin 1E

in examples in the book if its important its always given so I assume it will be.

Haley Dveirin 1E

Catalysits are not soncumed. Intermediates are consumed. For intermediates you see it as the product in one of the steps and reactant in another step, so it cancels out. This is not the case for catalysts, they don't "cancel out" in this way.

Haley Dveirin 1E

How do you find what A is in the term ln(A) in the Arrhenius equation. Like if you are using the Arrhenius equation to solve for Ea or K how do you know what to plug in for ln(A)? Is there some sort of table that has A values for different runs in the book? Or do we solve for that algebraically?

Haley Dveirin 1E

Yes we assume standard conditions

Haley Dveirin 1E

I believe so. The constants and equations link on his website takes you to the constants and equations paper that will be provided on the final.

Haley Dveirin 1E

I think the only difference is that in the book they round 0.0236 to 0.024 before plugging it into the last equation which slightly changes the answer from 756 seconds to 744 seconds (which using sig figs and scientific notation is 7.4 * 10^2).

Haley Dveirin 1E

I don't think it matters which one because B is 1.25 in experiment 1 and 2

Haley Dveirin 1E

In homework problem 7D5 how do you know ln(A)=-0.59?

Haley Dveirin 1E

I am getting the same answer as well. I think it is an error in the solution manual.

Haley Dveirin 1E

For a second order reaction it gives a straight line.

Haley Dveirin 1E

One of the bullets on the thermodynamics outline says "Use a ‘Chemisty’ van't Hoff analysis to calculate ∆H°, ∆S° and ∆G°." Can someone explain this?

Haley Dveirin 1E

One of the bullets on the second pager of the thermodynamics outline says "Understand why reaction free energy depends on pressure and the equilibrium constant." Can someone explain this?

Haley Dveirin 1E

After thermodynamics, what is test 2 going to cover up to?

Haley Dveirin 1E

When is it necessary to use Pt(s) in the skeletal equation of a redox reaction?

Haley Dveirin 1E

How do you find n? does it have to do with moles like the variable n has in the past or is it the number of electrons being transferred?

Haley Dveirin 1E

In Galvanic cells the electrodes flow from cathode to anode.

Haley Dveirin 1E

Yeah so E^o(cell) is given to be -0.689V. In the table 6M1 E^o of the anode half reaction Cu2+ + 2e- -> Cu is given as +0.34. So the equation would be:
E^o(cell)=E^o(cathode)-E^o(anode) which is -0.689=E^o(cathode)+0.34. Then you solve for E^o(cathode)

Haley Dveirin 1E

Yeah you assume there is water so the half reactions are:

O2+2H2O+4e- -> 4OH-
o2+4H+4e- -> 2H2)

Haley Dveirin 1E

I don't think we have finished 6N. I think we're in the middle of it

Haley Dveirin 1E

delta S and delt U are 0 because the final and initial state of the system is the same (ends up being 100.0L and 1.0atm in the end again) and because U and S are state functions it means the change is 0. As for q and w, I have no idea i need help with those too

Haley Dveirin 1E

When do you use the constant R=8.314 vs 8.206x10^-2 and what are the units for each

Haley Dveirin 1E

Does someone want to be a life saver and post an attachment that shows their work for the pizza rolls worksheet because only the final answers were posted. It would be greatly appreciated!

Haley Dveirin 1E

A reaction is spontaneous of S is positive and G is negative. If the product is more stable than the reactant.

Haley Dveirin 1E

Its just saying that all of those are state variables.

Haley Dveirin 1E

Entropy is basically the randomness and disorder of molecules in a system and is based on the different arrangements available to the molecules.

Haley Dveirin 1E

Yes. In simpler terms, it essentially means that entropy always increases.

Haley Dveirin 1E

because in the ideal gas equation: PV=nrT P and V are inverses (as one increases the other decreases)

Haley Dveirin 1E

Do we need to memorize the standard enthalpy of formation for different molecules??

Haley Dveirin 1E

In the text book problem 4C.3 why is nCp=5/2*8.314? Where does the 5/2 come from?

Haley Dveirin 1E

Multiply

Haley Dveirin 1E

You can use the pKb to find the Kb and then use the Kb to find the Ka. Then create your ICE table and set that equal to the Ka you found to solve for x which equals [H30+]. The use [H30+] to find pH and use pH to find pOH.

Haley Dveirin 1E

In problem 4A7 where does the constant 4.18J/(Cg) come from? (this constant is used in the solution manual but not given in the problem)

Haley Dveirin 1E

Do you use a different equations to calculate work done in a reversible or irreversible expansion?

Haley Dveirin 1E

What is the difference between enthalpy and heat?

Haley Dveirin 1E

So in the case of 4B 5 the units of w are L atm so you have to multiply it by 8.31447 J/mol K and then divide it by 0.08206 L atm/mol K in order to get the units to be J.

Haley Dveirin 1E

Do we need to memorize any Ka or Kb values for Test 1?

Haley Dveirin 1E

Does anyone know if the normal step-up up sessions and workshops that are held on Mondays are still being held tomorrow despite it being MLK Day???

Haley Dveirin 1E

Can someone explain how to solve this and what the answer is:

0.482 mol N2 and 0.933 mol O2 are placed in a 10.0 L reaction vessel and form N2O (dinitrogen oxide): 2N2(g) + O2(g) ⇌ 2N2O(g) KC = 2.0 x 10-37  What is the composition of the equilibrium mixture?

Haley Dveirin 1E

27. A mixture of 2.5 moles H2O and 100 g of C are placed in a 50 L container and allowed to come to equilibrium subject to the following reaction: C(s) + H2O (g) ⇌ CO (g) + H2 (g) The equilibrium concentration of hydrogen is found to be [H2] = 0.040 M. What is the equilibrium concentration of water,...

Haley Dveirin 1E

Part E is different from part D (no change) because there is 1 mole of the gas on the reactant side but two moles on the product side (looking at the sum of the coefficients, not the sum of the total number of elements) and therefore the reactants would be favored if the pressure was increased becau...

Haley Dveirin 1E

when writing the equilibrium constant for water, why do we omit [H20] from the expression?

Haley Dveirin 1E

do changes in pressure and volume affect K? if not, why not? if it does, how does it affect it?

Haley Dveirin 1E

I'm a little confused on Le Chatelier's Principle, can someone define exactly what it is and explain why the in class example Lavelle gave with it? N2+3H2=2NH3 He said that if N2 were increased, NH3 was increased, and H2 was decreased, the only way to increase the yield of NH3 without adding more re...

Haley Dveirin 1E

a change in concentration of a reactant causes the concentration of the product to change (and vice versa) so the ration of P/R does not change because both P and R change, meaning K does not change.

Haley Dveirin 1E

partial pressure is used for gasses. for aqueous things you don't need partial pressure.

Haley Dveirin 1E

a. the second situation will have more O2 because the only thing changing is the moles of O3 (not the volume of the flask) so the concentration of O3 is greater so the concentration of O2 must also be greater. For b. the partial pressure of O2 will be higher in the second situation because if there ...

Haley Dveirin 1E

When will the marshmallow answer key be posted?

Haley Dveirin 1E

When will the marshmallow answers be posted?

Haley Dveirin 1E

Yes it can be found on his website.

Haley Dveirin 1E

How do you know if an oxide will form an acid or base when added to water?

Haley Dveirin 1E

How do you know if an oxide is basic, acidic, or amphoteric?

Haley Dveirin 1E

The acid with the lower PkA is always stronger.

Haley Dveirin 1E

Because if one is more electronegative than the other it will cause there to be a partial negative where the more electronegative element is and a partial positive where the less electronegative element is.

Haley Dveirin 1E

Because Lavelle sent an email of ligand names we should know and those were included, I think we need to memorize them.

Haley Dveirin 1E

Intramolecular forces involve the sharing or exchange of electrons while intermolecular forces involve fluctuating electron distribution.

Haley Dveirin 1E

I typed in the link in my textbook into my computer but the page said error. I am going home for thanksgiving and really didn't want to have to take the textbook with me in my backpack.

Haley Dveirin 1E

The ligand is polydentate if it has more than 1 atom with a lone pair that can bind to a metal central atom. The number of atoms with a lone pair is the number of sites it can bind to the central metal atom.

Haley Dveirin 1E

Is there a way to access the chemistry textbook online?

Haley Dveirin 1E

Some of the problems in the assigned homework for the coordination compound unit asks about radicals. Do we need to know what that is and if so can anyone explain it?

Haley Dveirin 1E

1. Ion-Ion
2. Hydrogen Bonds
3. Ion-Dipole
4. Dipole-Dipole, Dipole-Induced Dipole, Induced Dipole-Induced Dipole (these are all usually similar in strength, about -2KJ/mol)

Haley Dveirin 1E

Most molecules are spherical but molecules with multiple Carbon atoms often form chains with other atoms (usually Hydrogen) coming off each carbon which creates a rod shaped molecule. For example, Pentane (C5H12).

Haley Dveirin 1E

They are two different shapes/structures but are both called linear just like there is a Bent for three regions of electron density and a Bent for four regions of electron density.

Haley Dveirin 1E

I would just to be safe. I think you should know all the VSEPR shapes listed on the worksheet handed out in your discussion section which includes those.

Haley Dveirin 1E

In the textbook the question 2F.5 asks: state the hybridization of the first atom in each of the following molecules and ions:
a) BeCl2 b) BH3 c) BH4-

Can someone explain how you solve these?

Haley Dveirin 1E

In the Lewis structure the central O atom has one set of lone pair electrons and then three hydrogens. Since it has 4 areas of electron density it is tetrahedral which has bond angles of 109.5. But since one of the regions is a lone pair, this pushes the other atoms away a little bit (because it has...

Haley Dveirin 1E

In the Lewis model the central N has no lone pairs (it is three Ns with the two outside Ns double bonded to the inner N) so it is Linear so the bond angles are 180.

Haley Dveirin 1E

I think its n, l, and both of the m's (m sub l and m sub s)

Haley Dveirin 1E

Is there an answer key for the VSEPR worksheet we got during our discussion section? If not, does someone know the answer to d. and f.

Haley Dveirin 1E

If a question asks you to identify the types of attractive intermolecular interactions that might arise between molecules of a substance (for example NH2OH) how do you know which ones? The answer for NH2OH is dipole-dipole and induced dipole-induced dipole but how do you know?

Haley Dveirin 1E

I think that the more polarizable the atom is, the more the covalent bond will have ionic characteristics, and ionic bonds are usually solid.

Haley Dveirin 1E

Because, for example, rod-shaped molecules when they bond can be closer together than two spherical molecules and therefore their bond is stronger.

Haley Dveirin 1E

There is a negative sign because the EP is always negative because it is always an attractive force.

Haley Dveirin 1E

Why does bond length increase with atom size?

Haley Dveirin 1E

So with hydrogen bonds and the intermolecular forces (ion-dipole, dipole-induced dipole, etc.) are electrons actually being transferred from one atom to another or shared between atoms or is it all just based on attraction?

Haley Dveirin 1E

They are the attractive forces responsible for condensed phase (liquid and solid). They include:
ion-ion
ion-dipole
dipole-dipole
dipole-induced dipole
induced dipole-induced dipole

Haley Dveirin 1E

How do we know which elements/when they can have more than 8 valence electrons?

Haley Dveirin 1E

If the electronegativity difference is between 1.5 and 2 then you can't say whether it is covalent or ionic.

Haley Dveirin 1E

Resonance structure just shows all the possible lewis structure for a molecule. NH4 does not have resonance.

Haley Dveirin 1E

electrons have such a small mass that the mass of the atom is essentially the same as the ion.

Haley Dveirin 1E

The atomic radius trend and ionization energy applies to the noble gasses but electron affinity and electronegativity does not.

Haley Dveirin 1E

Unlike the p-shell, the d shell can fit 10 e-

Haley Dveirin 1E

Weekly, from one Sunday to the next.

Haley Dveirin 1E

Count the valence electrons and if the number is closer to 8, it gains however many it needs to reach 8. If it is closer to 0, it loses however many necessary to get to 0. For d block elements, valence electrons in the s orbit move down to the d orbit and then it will gain however many electrons nee...

Haley Dveirin 1E

As of right now, if we've been posting at least 5 times each week, how many posts should we have made in total? Because I have been posting 5 times a week and have a total of 15 posts but I feel like we've been doing this for more than 3 weeks or is 15 correct?

Haley Dveirin 1E

Yeah resonance is a blending of structures with the same arrangement of atoms but a different arrangement of electrons. It spreads multiple bond characteristics over a molecule and essentially "blends" the different Lewis Dot structures for that molecule.

Haley Dveirin 1E

I think everything we have covered up to the midterm will be on it. So the high school review stuff, the quantum world, and chemical bonds.

Haley Dveirin 1E

how come when the book asks you to give the ground-state electron configuration for Ni^2+, the answer is [Ar]3d^8 and not [Ar]3d^64s^2?

Haley Dveirin 1E

The Electron affinity= energy of the atom - the energy of the anion created when the atom gains a(n) electron(s)

Haley Dveirin 1E

Yes, going down the table adds shells so the atomic radius gets bigger and the quantum number n increases.

Haley Dveirin 1E

For chromium the valence electrons would be both the electrons in the 4s and 3d state because chromium has 6 valence electrons.

Haley Dveirin 1E

For problem 1B.23 it gives the wavelength of a neutron and asks you to find the velocity. I used De Broglies Equation (wavelength= h/(mass x velocity) and plugged in h and wavelength to solve for velocity, but how do I find the mass of the neutron?

Haley Dveirin 1E

Question 1A.11 asks what is common to the lines within a series that makes grouping them together logical (referring to the Balmer and Lyman series). I don't understand the explanation the solution manual gives. Can someone explain?

Haley Dveirin 1E

On the test we took the formulas were given but I would memorize them just in case and also understanding the formulas helps you understand the concepts. As for the constants- I think those will always be given.

Haley Dveirin 1E

Are there any other series like this other than the Lymen series that we need to memorize?

Haley Dveirin 1E

I don't think rounding errors will be an issue as long as you are following the sig fig rules.

Haley Dveirin 1E

In problem F13 it asks you to name the compound PCL^5 (5 is a subscript) and the answer is Phosphorus Pentacholide. How do you know its chloride as opposed to chlorine/are there any other name-related things we should know?

Haley Dveirin 1E

Hi this may be a dumb question but I can't figure out how to post a new topic/question? So far all of the questions I have asked I posted as replies to another persons question because I couldn't find any button that says "post a new topic" but I could find the "post a reply" but...

Haley Dveirin 1E

For sig figs, do we round to the correct number of sig figs at the end or do we constantly round to the correct number as we go?

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