CHEMISTRY COMMUNITY

Sarah_Kang_2K

When pressure increases, the gaseous molecules on both sides of the reaction increasingly collide with each other. In order to alleviate/compensate for these increased collisions, the reaction favors the side with the less number of moles of gaseous molecules.

Sarah_Kang_2K

You can ignore x when approximating (when K<10^-3), but make sure to check your work after to make sure x is indeed less than or equal to 5% deprotonation!

Sarah_Kang_2K

Le Chatelier's principle predicts how the equilibrium will shift in response to changes in volume, temperature, pressure, the addition or removal of gaseous molecules, etc.

Sarah_Kang_2K

E˚is under standard conditions (pressure=1 bar, concentration= 1 mol/L, etc.)

Sarah_Kang_2K

The final will cover all of the material we've learned this quarter.

Sarah_Kang_2K

This is really helpful, thank you!

Sarah_Kang_2K

When it says "write the balanced half reactions", does this mean balance O's and H's, as well as electrons?
Or is it just like Cu2+(aq)--> Cu(s)

Sarah_Kang_2K

According to the textbook, the terms "stable" and "unstable" refer to the thermodynamic tendency of a substance to decompose into its elements. Furthermore, a thermodynamically stable compound just means a compound that has a negative standard Gibbs free energy of formation. So i...

Sarah_Kang_2K

On Outline 4, one of the bullet points listed says: "Understand why reaction free energy depends on pressure and the equilibrium constant". If someone could please clarify what this means, or direct me to the relevant section in the textbook (6th ed.) that talks about this, that would be m...

Sarah_Kang_2K

Delta G must be negative in order for a reaction to be spontaneous.

Sarah_Kang_2K

Gibbs free energy is an extensive property.

Sarah_Kang_2K

Calculating K for reverse reactions involves taking the inverse of K for the forward reaction (1/K)

Sarah_Kang_2K

Delta U = 0 for any isothermal expansion of an ideal gas, it doesn't have to be reversible.

Sarah_Kang_2K

I believe this has been posted on the forum already, but I can't seem to find the thread, but for the change in entropy formula due to changes in temperature, do we use: delta S = nCln(T2/T1) or do we use delta S = Cln(T2/T1) I'm confused as to how we include the number of moles (n) into the formula.

Sarah_Kang_2K

Temperature is negatively proportional to entropy change. Thus, higher temperatures result in smaller values of the change in entropy.

Sarah_Kang_2K

They mean the same thing: essentially that no work is done by the system.

Sarah_Kang_2K

Professor Lavelle mentioned the midterm would cover up to the end of entropy.
For the 6th edition textbook, what chapter/section does this correlate to? Are we responsible for Chapter 9 up to 9.10 (Overall Change in Entropy)?

Sarah_Kang_2K

I jumped around too, but found the textbook chapters to be helpful in gaining a conceptual understanding before trying to solve the problems.

Sarah_Kang_2K

Yes we should complete the problems from the thermochemistry material.

Sarah_Kang_2K

Can anyone please fill me in on what Dr. Lavelle went over in class this past Wednesday? I wasn't able to make it due to traffic. Thank you in advance!

Sarah_Kang_2K

I assume so, since we've done practice problems on it.

Follow up question: Does anyone know if we'll be tested on solutions of salts of polyprotic acids?

Sarah_Kang_2K

For Test 1, what do we need to know about pH of weak acid/base and its salt? Should we just know how to solve it, or do we need a deeper conceptual knowledge of it? I'm a little confused because we didn't go over this in discussion last week. If someone could clarify, that'd be great!

Sarah_Kang_2K

For Test 1, what should we know about the pH of weak acids and weak bases and its salt? We didn't go over this in discussion. Do we just need to know how to calculate it?

Sarah_Kang_2K

I'm a bit confused on how we use Ka and Kb to predict the strengths of acids and bases. Particularly, how we use Kb In lecture, we learned that if Ka > 10^3, this indicates a strong acid and if Ka < 10^-3, this indicates a weak acid. Does this logic apply to bases too? So if Kb>10^3, does this indic...

Sarah_Kang_2K

If the problem doesn't specify whether to use partial pressure or molar concentrations, how do we know which to use? For example, if a problem gives us the initial molar concentrations of the gaseous reactants, but doesn't specify whether to use partial pressures or concentrations, do we automatical...

Sarah_Kang_2K

In Example 11.7 (Calculating the equilibrium composition by approximation) of the 6th edition textbook, the problem tells us to solve for partial pressures. I tried using both partial pressures and molar concentrations to solve this problem, but when I used the concentration, it gave me a different ...

Sarah_Kang_2K

Questions will give us the pH or some other measures that will allow us to calculate the pH or pOH of the substance.

Sarah_Kang_2K

Thank you!!! Much appreciated.

Sarah_Kang_2K

Would anyone be able to inform me of what we covered in lecture today 11/14?
I wasn't able to make it. Thanks in advance!

Sarah_Kang_2K

The TA's go through the discussion forum at the end of the quarter, and as long as you post at least 3 times a week, you will get the full 30 points for the chemistry community discussion forum!

Sarah_Kang_2K

Solids aren't included in the equilibrium constant because there is no such thing as "concentration of a solid".
For liquids, liquids act as a solvent, and the change in concentration of a solvent is insignificant. Thus, we don't include pure liquids in the equilibrium constant.

Sarah_Kang_2K

Homework questions are a separate category. We get 7 points a week for homework and 3 points a week for chemistry community posts, given that you do all of them.

Sarah_Kang_2K

Professor Lavelle usually doesn't post the lecture slides, but if you look at the audio-visual topics, you should be able to find a video that covers what we went over in class yesterday.

Sarah_Kang_2K

Will we need to know how to do this for the final?

Sarah_Kang_2K

For binary acids, the more polar the H-A bond/the greater the electronegativity of A, the stronger the acid H-A the weaker the H-A bond, the stronger the acid For oxoacids, the greater the electronegativity of the central atom, the stronger the oxoacid the greater the # of oxygen atoms attached to t...

Sarah_Kang_2K

Do we need to know how to calculate the pH of salt solutions with an acidic cation or a basic anion? (this is from 12.13 in the 6th edition)

Sarah_Kang_2K

You add an H+ ion to a base to make a conjugate acid, and remove an H+ ion from an acid to make a conjugate base.

Sarah_Kang_2K

Hi guys.
What do we need to know about Acids and Bases for Test 3?

Sarah_Kang_2K

Yes, Test 3 will pick up where the Midterm left off.

Sarah_Kang_2K

You should refer to page 79 of the textbook for a summary of the 2 concepts!

Sarah_Kang_2K

Water is considered the universal solvent because: Water molecules carry partial charges (the hydrogen side of the water molecule carries a slight positive electric charge, while the oxygen side carries a slight negative electric charge). This structure allows water molecules to dissociate ionic com...

Sarah_Kang_2K

Unhybridized orbitals refer to your standard s, p, d, f orbitals. Hybridized orbitals pertain to electrons that can exist between these orbitals. Someone correct me if I'm wrong?

Sarah_Kang_2K

They passed the midterms back after lecture last Wednesday.

Sarah_Kang_2K

There is no lecture tomorrow.

Sarah_Kang_2K

The syllabus says the class isn't curved, but I believe Dr. Lavelle may use a slight curve once all the scores are in.

Sarah_Kang_2K

Electron diffraction supports the idea of light having wave-like properties, in addition to particle-like properties. Thus, De Broglie's Hypothesis is best supported by this.

Sarah_Kang_2K

Does anyone know if we get our midterms back after lecture today?

Sarah_Kang_2K

Can we do problems from Outline 3 for this week's hw?

Sarah_Kang_2K

Also, what should we know about Lewis acids and bases?

Sarah_Kang_2K

Dr. Lavelle mentioned that we are only responsible for Bonding up to 3.11. However Outline includes concepts about electronegativity and ionic and covalent bond length. Does this mean that electronegativity, strengths of ionic and covalent bonds, bond lengths, covalent bond dissociation energy, etc....

Sarah_Kang_2K

Will we need to know how to use the formula for coloumb potential energy of interactions for the midterm today??
It's the formula that's in Chapter 3.4 of the 6th edition.
It isn't stated on the outline, but just wanted to make sure.

Sarah_Kang_2K

Where is our midterm held today???

Sarah_Kang_2K

You can also post on the Free and For sale page on Facebook and see if anyone is renting or selling theirs!

Sarah_Kang_2K

You should also know the relationship between wave function and probability density (wavefunction^2).

Sarah_Kang_2K

For our upcoming midterm, what should we know about atomic orbitals? In Outline 2, it says to be able to describe the interpretation of atomic orbitals in terms of probability. Does this mean we should know the formulas for spherical polar coordinates, radical wave function, angular wave function, e...

Sarah_Kang_2K

Will we be tested on Shrodinger's equation for Test 2?

Sarah_Kang_2K

Is this from Outline 2 or 3?

Sarah_Kang_2K

I am wondering this too.

Sarah_Kang_2K

Would anyone be able to share their notes from monday lecture with me? I wasn't able to make it. If so, if you could email me at sarah27kang@gmail.com, it'd be greatly appreciated!

Sarah_Kang_2K

Oh okay thank you!

Sarah_Kang_2K

For Test 3 that starts in discussion section November 20th, does anyone know when the Thursday/Friday sections will take the test, since it's Thanksgiving break starting Thursday?
Thanks!

Sarah_Kang_2K

Yes, Teest #2 covers topics on Outline #2.

Sarah_Kang_2K

Yes, we are still in the Quantum section! He mentioned in lecture not to do questions from the Fundamentals section, for the Week 3 homework.

Sarah_Kang_2K

I think it's best to take notes by hand, and then after lecture that night, re-read your notes and highlight important topics as well as read confusing topics in the textbook.

Sarah_Kang_2K

They sell erasable pens on Amazon. I'd also recommend bringing white-out just in case you need to correct something!

Sarah_Kang_2K

In the equation, E=hv where v = frequency, what is the difference between intensity and frequency of light? In lecture, Professor Lavelle mentioned increasing the intensity of the light does not increase the energy of the individual photon. So, frequency and intensity can't refer to the same thing, ...

Sarah_Kang_2K

Hi all,
I was unable to attend lecture today due to a family event back home. Would anyone be willing to share a picture of their notes with me so that I can catch up on what I missed?

If so, could you please text me at 805-708-6286?

Thank you.

Sarah_Kang_2K

Hi Christine,
Okay thanks so would the TI-30 calculators be allowed? Scientific calculators are ones that still allow us to calculate 6.022X10^23 and exponents, right?

Sarah_Kang_2K

Hi. For Chem 14A, are we allowed to use TI-84 calculators on the exams?
If not, could somebody please tell me which calculators are allowed? TI 30 calculators perhaps?

Thank you!

Sarah_Kang_2K

Yes, you need to take into account subscripts when finding the molar mass of a compound. For example, in order to find the molar mass of CO2, you would add the molar mass of carbon plus twice the molar mass of oxygen. This gives you the molar mass of CO2. You can then use the molar mass of CO2 and t...

Sarah_Kang_2K

Cl on its own would refer to the ion form (Cl-). Cl2, along with N2, H2, and O2 are all gaseous forms of the elements.

Sarah_Kang_2K

On Question E.21.d of the 6th edition textbook, the first step is to calculate the molar mass of glucose (C6H12O6). I am confused as to why the final molar mass contains 5 sig fig's and not 4. Here is my work: 6(12.011) + 12(1.008) + 6(15.999) = 180.2 g/mol The textbook solutions states that the ans...

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