CHEMISTRY COMMUNITY

Alexa_Henrie_1I

If you google "Bruin Test Bank at UCLA" and click the Chemistry tab, there is a 14B final from Lavelle's Winter 2014 class.

Alexa_Henrie_1I

When absolute temperature equals zero (T=0), there is no thermal entropy (no movement). This means that residual entropy is based on the complexity and order of the molecule and its positions.

Alexa_Henrie_1I

Question 15.85 asks us to draw a proposed structure for the activated complex of each chemical reaction given. Will we be required to know how to draw these structures for the final?

Alexa_Henrie_1I

Could someone who got this question correct explain step by step how they did it? I am still confused with this problem.

Alexa_Henrie_1I

I am also confused as to why that conversion doesn't apply to galvanic cells.

Alexa_Henrie_1I

Why is Q [H+]1/[H+]2?

Alexa_Henrie_1I

Many homework problems ask to solve for the temperature at which a reaction is spontaneous. This shows that spontaneity depends on more than it just being exothermic or endothermic and understanding this makes solving these problems easier.

Alexa_Henrie_1I

Yes the final is cumulative and I would focus more on 14B material than things taught in 14A.

Alexa_Henrie_1I

Yes, we normally get our tests back the following week in discussion.

Alexa_Henrie_1I

Even though we won't be directly tested on Enthalpy and Entropy, we still need to know how to calculate them to use in Gibbs Free Energy so I would make sure to still review them.

Alexa_Henrie_1I

If you have the sixth edition text book there are homework problems in chapter 11 that deal with the Van't Hoff's equation!

Alexa_Henrie_1I

When G=0, there is no energy free to do work.

Alexa_Henrie_1I

It would be the reaction's natural tendency to go from a liquid to a gas at T=boiling point.

Alexa_Henrie_1I

What do you do with a sick chemist?
If you can't helium, and you can't curium, then you might as well barium.

Alexa_Henrie_1I

They are normally handed out after lecture, not in discussion.

Alexa_Henrie_1I

We will be tested on Friday's lecture material up to Gibbs Free Energy.

Alexa_Henrie_1I

Residual entropy is positional entropy. We can find it using SkblnW (this ignores thermal energy).

Alexa_Henrie_1I

I am also confused about this problem. My answer doesn't match the solutions manual either.

Alexa_Henrie_1I

The universe is also considered an isolated system because the energy of the universe is constant.

Alexa_Henrie_1I

Lavelle said they are interchangeable so you could use either as long as the answer matches the units.

Alexa_Henrie_1I

There are some problems in the text book where the integral equation is needed (for example problem 8.11 in the sixth edition) so I would know how to solve for those.

Alexa_Henrie_1I

Lavelle posted the modules for only the first two sections in Chem 14A, so he may only post chemical equilibria modules for 14B.

Alexa_Henrie_1I

Work is dependent on the path taken because the intermediate steps taken to get to the final conclusion must be considered rather than just calculating final-initial.

Alexa_Henrie_1I

Another way to determine whether a reaction is endothermic or exothermic is by the value of delta H: an endothermic has a positive delta H because the reaction is absorbing energy, whereas an exothermic energy has a negative delta H because it is releasing energy.

Alexa_Henrie_1I

We can take this short cut when the value of K is < 1x10^-3

Alexa_Henrie_1I

Okay I understand how the Kw is equal to to x^2 now. Thank you.

Alexa_Henrie_1I

Hello, I am having trouble solving 12.23. Could someone please explain how to go about it? The question asks: The value of Kw for water at body temp (37 degrees C) is 2.1x10^-14. A) What is the molarity of H3O ions and the pH of neutral water at 37 degrees C? B) What is the molarity of OH in neutral...

Alexa_Henrie_1I

Q can be calculated at any given time, whether before equilibria is reached or after equilibria is subjected to change. It's just a measure to see whether more reactants or products are being formed until reaching equilibrium.

Alexa_Henrie_1I

Will we need to know the Gibbs Free Energy equation for the first test?

Alexa_Henrie_1I

Is dien tridentate or tetradentate?

Alexa_Henrie_1I

A conjugate base is the result of an acid donating its protons.
A conjugate acid is the result of a base accepting protons.

Alexa_Henrie_1I

Anions get larger as the number of electrons increase because the number of shells increase. Ionic radii increases down a group and decreases across a period. So determining size of anions does depend on the number of electrons but you also have to consider the strength of the nuclear charge and its...

Alexa_Henrie_1I

Yes, quick means "active" and slake means to hydrate. This makes sense because calcium hydroxide is formed by mixing calcium oxide with water.

Alexa_Henrie_1I

Okay, hopefully they will be provided on the final.

Alexa_Henrie_1I

Are we expected to memorize all of the common ligand names from Table 17.4 (6th edition)?

Alexa_Henrie_1I

The best way to know bond angles is to memorize which bond angles are formed by each shape. Remember that lone pairs can effect these bond angles through repulsion and bond angles would therefore be a little smaller than without lone pairs attached to the molecule.

Alexa_Henrie_1I

https://goo.gl/images/4c7DMC

This link shows a good representation of an induced-dipole.

Alexa_Henrie_1I

^this is correct. Atoms with higher electronegativity attract electrons more than atoms with low electronegativity, resulting in a net dipole moment. Remember that electronegativity increases across a period and decreases down a group.

Alexa_Henrie_1I

^This chart is super helpful thank you for sharing it!

Alexa_Henrie_1I

So the best way to know the angles is just through memorization of the structures right?

Alexa_Henrie_1I

^Exactly. Higher melting points indicate more stability so this explains the example given in class: GC base pairs in DNA are more stable than AT base pairs.

Alexa_Henrie_1I

Yes to confirm the last test begins in your discussion section the week of November 26th.

Alexa_Henrie_1I

I am pretty sure than 93 is an A

Alexa_Henrie_1I

Polarizability depends on the number of electrons a molecule has and its size. Increasing size and electrons results in stronger attractive interactions.

Alexa_Henrie_1I

A faster way to find a radical is by counting how many electrons a molecule has. An odd number of electrons would signify a radical whereas an even number of electrons would signify paired electrons.

Alexa_Henrie_1I

Yes the position in question 1 is just the diameter, 2x10^-4 m.

Alexa_Henrie_1I

If there are only two atoms in a molecule, does it matter where the atom with the non-lowest ionization atom is put? Like does it matter if it is put to the left or right of the central atom?

Alexa_Henrie_1I

Second ionization energy is always higher because after the first electron is removed, the atom is more positive and the protons in the nucleus have a stronger pull on the electrons left

Alexa_Henrie_1I

We write the d group in electron configurations before p groups because the d state is lower in energy than the p state

Alexa_Henrie_1I

It also helps to consider why cations are smaller than their neutral atoms. Cations are smaller because they lose an electron, which decreases the size of the electron cloud.

Alexa_Henrie_1I

Okay this makes sense. Thank you so much!

Alexa_Henrie_1I

I don't really understand 2.29, the question asks to identify how many electrons can have the following quantum numbers in an atom. I don't know how to figure out the possible number of electrons that can have a specific quantum number. Can someone explain how to do this?

Alexa_Henrie_1I

Nothing from test 1 will be on test 2

Alexa_Henrie_1I

First plug in n=4 into the formula to solve for the energy at that level. Then do the same for n=2. After calculating these answers, find the difference between the two using Energyfinal-Energyinitial. Finally plug this difference into equation: wavelength=h(c)/E.

Alexa_Henrie_1I

Solve for the energy at n=6 and energy at n=5. After finding these two numbers, subtract Energyfinal-Energyinitial. Once you find this difference, plug the answer into equation: wavelength=h(c)/E

Alexa_Henrie_1I

and mass of e- will always be 9.11x10^-31 for that equation right?

Alexa_Henrie_1I

You only need to know the molar ratio between the limiting reactant and products because the limiting reactant is completely used in the chemical reaction.

Alexa_Henrie_1I

Thank you both so much! I just wasn't using .02 L as the initial volume in the equation. Seeing it step by step helped a lot!

Alexa_Henrie_1I

I am having a hard time solving question 25 on the Molarity and Dilution post assessment. The question is: 5.00 g of KMnO4 is dissolved in a 150.00 mL flask of water. If 20.00 mL of this solution is removed and placed in a new 2nd 250.00 mL flask and filled with water, what is the concentration of t...

Alexa_Henrie_1I

percent yield= actual yield (which will be given to you)/theoretical yield

Alexa_Henrie_1I

Just to clarify, when determining molar mass of a reactant you don't include the coefficient that was found when balancing the equation right?

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