CHEMISTRY COMMUNITY

VLi_2B

When something is reversible, it is also isothermal.

VLi_2B

When balancing in basic solution don't forget to use OH^-

VLi_2B

I would go over the outlines that Lavelle has posted on his website, and make sure you understand each bullet point.

VLi_2B

This video is pretty good at explaining the concepts.
https://www.khanacademy.org/science/che ... tion-order

VLi_2B

Hi for problem 1D in the review, will Ecell decrease or stay the same?

true/false Ecell will increase if the size of the anode metal is increased.

VLi_2B

No, you only need to know what is on the Electrochemistry outline.
https://lavelle.chem.ucla.edu/wp-conten ... rochem.pdf

VLi_2B

Depending on what order your reaction is, your rate law will be different. For zero-order and first-order reactions, the slope is equal to -k, but for second-order reactions, the slope is just k. The trick is just distinguishing which value is k when using a rate law. How can you tell the differenc...

VLi_2B

K = equilibrium constant has no units
k = rate constant units fluctuate between orders

0 order units: M/s, M/min, M/hr, etc.
1st order units: s-1, min-1, hr-1, etc.
2nd order units: M-1s-1, M-1min-1, M-1hr-1, etc.

VLi_2B

This is a good video explaining exothermic vs endothermic reactions.
https://www.youtube.com/watch?v=JRIm_a2LDPM

VLi_2B

Juliet Stephenson 4E wrote:What defines a solid conductor?

A solid conductor is a metal in solid state.

VLi_2B

Are you referring to n = moles and k = Rate?

VLi_2B

Intermediates are produced in one step and consumed in a later step, so they do not appear in the overall reaction equation or overall rate law

VLi_2B

TimVintsDis4L wrote:I wouldn't be surprised if we get our tests back on Wednesday as the Ta's might have to work on the final so they get the tests over with first.

Do the TAs make our final or Dr. Lavelle?

VLi_2B

Whenever you do your homework, always use the same instruments (pen and calculator) that you plan to use on the test. It'll eventually become muscle memory.

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You want the value to be positive because that means the reaction is spontaneous.

VLi_2B

In neutral solutions, you should use H2O to balance the hydrogens.

VLi_2B

I remember with the acronym OIL RIG.
OIL: oxidation is losing elections
RIG: reduction is gaining elections

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A single line represents interface between phases in contact with each other including a porous wall. A double line represents a salt bridge.

VLi_2B

It will be everything left from thermochemistry that we did not cover on the midterm and electrochemistry.

VLi_2B

Spontaneous processes don't necessarily happen quickly, it just means that over time there is a tendency for that reaction to occur. The equation that relates spontaneity to the cell potential difference is deltaGknot = -nFEknot. This makes sense, because the more positive the E value of cell poten...

VLi_2B

Are you referring to when you have to balance the half reactions?

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The direction of flow is always from the anode to the cathode.

VLi_2B

Are there any polyatomic ions that we should memorize or will we be provided with the charges of the ions?

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Angela Wu-2H wrote:Will test 2's difficulty be more like test 1's difficulty or the midterm's difficulty?

I heard that in the past quarters, test 2 has been harder than test 1.

VLi_2B

You need to first write out your balanced equation. The equation that you're going to want to use is w=-PdeltaV. You know that PdeltaV=deltanRT (ideal gas law).
From there, you can find that the delta n of the gaseous products is (6-7.5=1.5), and then you just plug in the other values.

VLi_2B

The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 8 C to 22.799 8 C. The calorimeter assembly is known to have a total heat capacity (calorimeter ...

VLi_2B

Intensive properties do not depend on the quantity of matter. Examples include density, state of matter, and temperature. Extensive properties do depend on sample size. Examples include volume, mass, and size

VLi_2B

When a process is reversible, is it also isothermal?

VLi_2B

Hi, I vaguely remember in Lyndon's review session about an acronym to help remember all the state functions. Can anyone refresh my memory?

VLi_2B

A reaction is spontaneous if delta G is negative and is not spontaneous if delta G is positive.

VLi_2B

Can someone please give an example of an isolated system that is not a bomb calorimeter or a hydroflask?

VLi_2B

Degeneracy is defined as having two or more quantum states in a quantized energy level. For example, 2p would have three degenerate orbitals, 2px 2py 2pz, because they are in the same n=2 energy level.

VLi_2B

When bonds form, you have an exothermic process.
When bonds break, you have an endothermic process.

VLi_2B

Water boils at 100 degrees Celsius also known as 373.15 degrees Kelvin

VLi_2B

I believe we will need to be able to calculate an integral because the pre-requisites to the class include math 31b or ls 30b.

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This is because it takes no energy to form a naturally-occurring compound.

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Kelvin = Celsius + 273.15

Celsius = Kelvin - 273.15

Because the difference between Celsius and Kelvin is addition/subtration; the difference/sum will always be the same.

VLi_2B

What is the difference between “spontaneous” and “energetically favorable”?

VLi_2B

Wait, but I assumed that heat would still technically be able to escape from a hydroflask to the surroundings. Are there any other examples that would be an isolated system?

VLi_2B

Can someone please explain what Dr. Lavelle was showing through his diagrams of Calorimeters?

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Ka × Kb = Kw = 10-14 at 25 °C

VLi_2B

https://lavelle.chem.ucla.edu/wp-conten ... ibrium.pdf
https://lavelle.chem.ucla.edu/wp-conten ... _Bases.pdf

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Q is the reaction quotient and expresses the relative ratio of products to reactants at a given instant. On the other hand, K is the equilibrium constant and is used to calculate the final concentrations at equilibrium for a reaction using an ICE table. If Q and K equal each other, the reaction is a...

VLi_2B

Solids and liquids are not included in the K expression as they do not change their concentrations in a reaction as they are pure substances. Essentially, their value is 1 resulting in the K expression only including aqueous solutions. As well as gases!! Wait, I thought gases were included in the K...

VLi_2B

The quick way is to count the number of moles on each side of the reaction equation and compare which side has the greater number of moles to determine which way the reaction will favor. N2(g) + 3H2(g) <=> 2NH3(g) Reactants: 1 mol of N2 + 3 mols of H2 Products: 2 mols of NH3 4 mols of reactant to 2 ...

VLi_2B

Dr. Lavelle's website also provides the constants and formulas that we will receive for test and exams.

https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf

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Only gaseous and aqueous forms of reactants and products are used in an equilibrium constant expression.

VLi_2B

This would be fun idea though!

VLi_2B

I believe Le Chatelier’s principle is found in section 5J on page 426.

VLi_2B

I believe chemistry community posts are due by 11:59 pm on Sunday.

VLi_2B

All amphiprotic species must be amphoteric, but the converse is not true.

VLi_2B

Where have people been able to find old tests?

VLi_2B

Are the numbers before hybridization just the period the element is in?

VLi_2B

Can someone please explain how I can figure out if something is a Lewis acid or base? And how do I know what the product will be? Draw the Lewis structure or symbol of each reactant, identify the Lewis acid and the Lewis base, and then draw the Lewis structure of the product (a complex) for the foll...

VLi_2B

The lecture on 11/22 was on Naming Coordinate Compounds and Acids and Bases.
The lecture on 11/27 was a continuation of Acids and Bases (mainly how to find pH), Relative Acidity, and pKa.

VLi_2B

I believe you should be able to know what the difference is between the two for the exam.

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See Attachment

VLi_2B

All Bronsted-Lowry bases are also Lewis bases, but the reverse is not true. Same for Bronsted-Lowry acids and Lewis acids. A Lewis acid is anything that accepts a pair of electrons, while a Bronsted acid accepts pairs of electrons only from hydrogen. A Lewis base is anything that donates a pair of e...

VLi_2B

Basically the same steps as a Lewis structure, but remember that the transition metals do not always follow the octet rule. You should pay attention to what atoms are bonded to the transition metal/Lewis acid and adding lone pairs and determining the formal charge is helpful.

VLi_2B

Can someone please clarify the difference between Lewis Acids and Bases and Bronsted Acids and Bases?

VLi_2B

Does anyone know if there will be a curve on the final?

VLi_2B

Will there be a curve on the final?

VLi_2B

Our hw 9 is due with our hw 10 so you should email your TA to find out the exact details.

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2E.5 (a) What is the shape of a ClO2+ ion?

How can you tell if something is bent or trigonal planar? Thanks!

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2E.25 Draw the Lewis structure and predict whether each of the following molecules is polar or nonpolar: (a) CH2Cl2; (b) CCl4; (c) CS2; (d) SF4.

How can I tell if molecules are polar or nonpolar?

VLi_2B

This has probably already been said, but can someone list all the topics that will be covered on this upcoming test

VLi_2B

First, I would draw out the lewis structure which should have the carbon in the middle with single bonds to two hydrogens and a double bond to an oxygen with two lone pairs.

Carbon and Oxygen are both sp2 hybridized

The H-C-O bond angle is 120 degrees

3 sigma bonds and 1 pi bond

VLi_2B

That's what I got!

VLi_2B

Although CH2Cl2 is symmetrical, the differing polarities of the C–H and C–Cl bonds means the effect of the polar bonds is not cancelled, so the molecule is polar

SF4 has 4 bonds with one lone pair which makes it polar.

VLi_2B

Electronegativity is the tendency of an atom to attract electrons, while electron affinity is the amount of energy released when an electron is added to a neutral atom.

VLi_2B

First, I would draw out the lewis structure which should have the carbon in the middle with single bonds to two hydrogens and a double bond to an oxygen with two lone pairs.

Carbon and Oxygen are both sp2 hybridized

The H-C-O bond angle is 120 degrees

3 sigma bonds and 1 pi bond

VLi_2B

A sigma bond is a bond formed by the overlap of orbitals in an end-to-end fashion, with the electron density concentrated between the nuclei of the bonding atoms. A pi bond is a bond formed by the overlap of orbitals in a side-by-side fashion with the electron density concentrated above and below th...

VLi_2B

On the midterm, will we need to find the electron configurations of elements past the f-blocks?

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2B.15 Draw the Lewis structures that contribute to the resonance hybrid of nitryl chloride, ClNO2 (N is the central atom).

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2C.11 Draw the Lewis structure and state the number of lone pairs on xenon, the central atom of each of the following molecules:
(a) XeOF2; (b) XeF4; (c) XeOF4.

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2C.17 Select from each of the following pairs of Lewis structures the one that is likely to make the dominant contribution to a resonance hybrid. Explain your selection. (pg. 94)

Can someone explain resonance hybrids and this problem?

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I believe that you can write the full configuration or the noble gas configuration. Either works

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I believe they are atomic radius, ionization energy, electronegativity, and electron affinity.

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Why are single bonds longer than double bonds?

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2B.23 Determine the formal charge on each atom in the following molecules. Identify the structure of lower energy in each pair. (The pictures are in the textbook on page 87)

Can someone please explain formal charges to me?

VLi_2B

On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds: (a) magnesium arsenide; (b) indium(III) sulfide; (c) aluminum hydride; (d) hydrogen telluride; (e) bismuth(III) fluoride.

VLi_2B

Can someone please explain the constants in the Rydberg Equation and when I would use it?

VLi_2B

Can someone please clarify which equations should be used for light and which ones should be used for particles?

VLi_2B

1D.25 Which of the following subshells cannot exist in an atom: (a) 2d; (b) 4d; (c) 4g; (d) 6f?

Can someone please explain this problem to me?

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Balance metals, then non-metals, and finally oxygen.

https://www.youtube.com/watch?v=mq3Mps6YqfU&app=desktop

VLi_2B

VLi_2B

First use the De Broglie equation:
λ = h/mv, where λ is wavelength, h is Planck's constant, m is the mass of a particle (g), moving at a velocity v (m/s)

Change and check units
125km/hr = 34.72m/s

λ = (6.6261 x 10^-34 m^2 kg/s)/ (275kg x 34.72m/s)
λ = 6.94 x 10-38 m

VLi_2B

Can anyone help clarify what the differences between the Balmer and Lyman series and what they are used for?

VLi_2B

D.19 How many orbitals are present in the (a) 4p-subshell; (b) 3d-subshell; (c) 1s-subshell; (d) 4f-subshell of an atom?

Can someone also explain why 3d is filled before 4s?

VLi_2B

Following!

VLi_2B

You should use Heisenberg's Indeterminacy Equation, delta p x delta x >= h/(4pi) First, change the diameter from 350pm to meters, 3.50 x 10^-10 m. Then plug in all known values into the Heisenberg equation to solve for Delta p. delta p = 6.63x10^-34/ (4pi x 3.50x10^-10m) Then, just use delta p = del...

VLi_2B

Can someone also explain why for the Lyman series the lowest energy level is n=1; for the Balmer series the lowest n=2; for the Paschen series it's n=3; and for the Brackett series n=4?

VLi_2B

Are there any specific equations we need to memorize for future tests? Or are equation sheets usually provided

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Round significant figures at the end

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996.08g = 339.20g Co + 656.88g F Find the mass % of each of the elements in the compound (339.20g Co) / (996.08g total) = 34.05% Cobalt (656.88g F) / (996.08g total) = 65.95% Fluorine Convert to moles (34.05g Co) / (58.93g / mol Co) = 0.5778 mol Co (65.98g F) / (19g / mol F) = 3.473 mol F Divide by ...

VLi_2B

I think it's 5 times a week, and you can choose whether to pose or answer questions.

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All the reactants and products are in gas phase, thus the net number of moles of gas produced should be the sum of coefficient of the product - the sum of coefficient of the reactants.
36-30=6

VLi_2B

(a) First balance the chemical equation: Al + Cl2 -> AlCl3. It should look like this once it's balanced: 2Al + 3Cl2 -> 2AlCl3 (b)You need to find to the limiting reactant so you should convert the masses of the reactants to moles and then compare the ratios of the stoichiometric coefficients to thos...

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