CHEMISTRY COMMUNITY

Lauren Huang 1H

It's also helpful to do the modules and go to office hours!

Lauren Huang 1H

You don't need to include it since anything to the zeroth power is equal to one.

Lauren Huang 1H

Although the products and reactants involved in Kp and Kc use units such as molarity and bar, the units cancel out in the end so K is unitless.

Lauren Huang 1H

So the reducing agent will have a high oxidizing power, and the oxidizing agent will have a high reducing power.

Lauren Huang 1H

Can someone please explain why Gibbs free energy for the combustion of a gas used to heat a BBQ at a pool party is negative? Wouldn't it require be a non-spontaneous process for the combustion to occur?

Lauren Huang 1H

I think they meant the Van't Hoff equation; it was provided to us on the equation sheet.

Lauren Huang 1H

The units can be atm or bar depending on the problem. Note that this will change the value of R.

Lauren Huang 1H

Q is when the reaction is not at equilibrium. K is when the reaction is at equilibrium. Q is compared to K to determine whether the reaction will shift to the left or right due to the Le Chatalier's Principle.

Lauren Huang 1H

How do we know if a redox reaction is acidic or basic if no H+ or OH- is given?

Lauren Huang 1H

Both can be calculated the same way. The only difference is that Q is when the reaction is not at equilibrium and K is when the reaction is at equilibrium.

Lauren Huang 1H

You should be able to ask for regrading. Just let your TA know and he/she should be able to help with that.

Lauren Huang 1H · Re: Final exam The final exam should be on Sunday, March 17 at 11:30am-2:30pm

The final exam should be on Sunday, March 17 at 11:30am-2:30pm

Lauren Huang 1H

H20 (l) is not included in the equation because water is in a much larger quantity in comparison to the rest of the reactants so the change in its concentration during a reaction is negligible.

Lauren Huang 1H

Also, Dr. Lavelle said in lecture that Gibbs free energy only refers to situations where the system is not at equilibrium, since delta G when the system is at equilibrium is zero.

Lauren Huang 1H

Question 9.47 in the sixth edition says: Initially a sample of ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate deltaS(tot), deltaS(sys), and deltaS(sur...

Lauren Huang 1H

Question 8.27 from the 6th edition says: Calculate the work for each of the following processes beginning with a gas sample in a piston assembly with T = 305 K, P = 1.79 atm, and V = 4.29 L: (a) irreversible expansion against a constant external pressure of 1.00 atm to a final volume of 6.52 L; (b) ...

Lauren Huang 1H

Question 8.43 for the 6th edition give the heat capacities of the different states in units of J/mol. Why is this? I thought the definition of heat capacity is the heat required to raise the temperature of an object by one degree. Wouldn't the units have to include degrees celsius or Kelvin?

Lauren Huang 1H

The second law of thermodynamics states that delta S=q/T=nRln(V2/V1). So q=nRTln(V2/V1) if you multiply both sides by temperature. I believe the unit for q is Joules.

Lauren Huang 1H

I believe Week 4 HW should be on the questions in the Thermodynamics section.

Lauren Huang 1H

Also, when your chemical reaction includes H30+, you are finding the pH, and when it includes OH-, you are finding the pOH. Make sure to use the equation pH+pOH=14 if you are trying to convert between the two.

Lauren Huang 1H

State property is a quantity that is determined by its current state but is not dependent on the path taken to obtain that state (ex: altitude, volume). Extensive property is a property of matter that depends on the amount of substance (ex: heat capacity).

Lauren Huang 1H

Table 11.2 has two columns of equilibrium constants denoted K and Kc. While the values are similar for the first few equations, it differs in the latter half. Does anyone know the difference between the two?

Lauren Huang 1H

I don't think we will have to know how to do that for this class. Here's the link that Dr. Lavelle sent out in an email on solving cubics: viewtopic.php?f=49&t=40016

Lauren Huang 1H

The lower the pKa, the higher the corresponding Ka is, which relates to increasing acid strength (stronger acids).

Lauren Huang 1H

Do we convert Kc to Kp or vice versa the same way we do for converting individual concentrations/partial pressures using P=(n/V)*(RT)?

Lauren Huang 1H

I personally think going to office hours is also really helpful since it is a good way to get some answers to the questions you might have after doing the homework problems.

Lauren Huang 1H

14. The two air pollutants SO2 and NO2 can react in the atmosphere as follows: SO2 (g) + NO2 (g) ⇌ SO3 (g) + NO (g) Predict the effect of the following changes to the amount of NO when the reaction above has come to equilibrium in a stainless steel bulb equipped with entrants for chemicals. i. The a...

Lauren Huang 1H

I think we were also allowed to turn in our homework during discussion for Week 1. It should be fine as long as you turned it in by the Friday lecture.

Lauren Huang 1H

If the reactants or products are gases, then you can usually use either Kp or Kc. However, you can only use Kc for reactions involving aqueous solutions.

Lauren Huang 1H

Since there are multiple values of R, make sure the units of the R you are using cancel out/correspond with the other units in the equation.

Lauren Huang 1H

Yes, the AXE formula can help you draw the shape of the structure, but it will not tell you the elements involved.

Lauren Huang 1H

It's essentially saying that the trend for s-character is the inverse of the trend for p-character.

Lauren Huang 1H

Will be get our test 3 back during discussion this week?

Lauren Huang 1H

The triple bond to nitrogen and single bond to chlorine would also be preferable since it satisfies the octet rule for carbon.

Lauren Huang 1H

Would it be ok if I wrote the bond angles for 3 bonds pairs and 1 lone pair to be 107.5, and the bond angles for 2 bond pairs and 2 lone pairs to be 104.5? Or would writing "less than 109.5 degree" be preferred?

Lauren Huang 1H

The head of the sigma bonds overlap directly while the pi bonds overlap laterally since they are parallel to each other, so it is easier to break the pi bonds.

Lauren Huang 1H

This is because the additional bonding of electrons attracts the nuclei of the bonded atoms closer to each other.

Lauren Huang 1H

This rule usually applies to most structures, where the central atom is the element with the lowest ionization energy and least electronegativity.

Lauren Huang 1H

They might also ask us about the differences between the two types of bonds.

Lauren Huang 1H

If the two lone pairs of Xe in XeF4 are placed opposite each other due to electron repulsion, why is it that the two lone pairs in H20 are placed next to each other?

Lauren Huang 1H

Memorizing them would definitely help you do the problems faster and focus on other parts of the problem.

Lauren Huang 1H

Are the notations that we are learning for hybridization only sp,sp2,and sp3?

Lauren Huang 1H

I would stick to the sig figs rules just to be safe.

Lauren Huang 1H

Sometimes nitrogen can be an added reactant and product of the equation.

Lauren Huang 1H

I did the problems after 3.11 since I believe professor Lavelle said we only needed to know the questions up to 3.11 for the midterm test

Lauren Huang 1H

Some common elements that have expanded octets are sulfur, phosphorus, silicon, and chlorine.

Lauren Huang 1H

Chromium and copper are the two main exceptions to electron configuration. For both elements, an electron from 4s subshell is moved to 3d subshell to make a half full 3d (3d^5) for chromium and a full 3d (3d^10) for Copper, since doing so makes the atom more stable. So for this problem, Cu at ground...

Lauren Huang 1H

When writing out the electron configuration for silver and antimony, why is 4d^10 before 5s when 4d^10 is after 5s in the periodic table?

Lauren Huang 1H

Can nothing be faster than the speed of light?

Lauren Huang 1H

Why is it that 3d is not on the same level as 3s and 3p on the periodic table?

Lauren Huang 1H

Will Test 2 covers all the questions from Ch. 2 since the questions cover electron affinity, atomic radius, ionic radius, ionization energy and the periodic trends? And if not, up to which questions would you say the test covers?

Lauren Huang 1H

Can someone help me explain how to do this question? 44. In the hydrogen atomic spectrum, what is the wavelength of light associated with the n = 4 to n = 1 electron transition? What part of the electromagnetic spectrum is this wavelength? Also will we be required to know the electromagnetic spectru...

Lauren Huang 1H

Can wavelengths have negative values?

Lauren Huang 1H

What does it mean when the answer from using the equation (E=-hR/n^2+hR/n^2) to find the energy difference between two energy levels in a H-atom comes out to be negative?

Lauren Huang 1H

You can also go to the TAs office hours or UA peer learning sessions.

Lauren Huang 1H

You still need a new set of 7 problems (from Fundamentals or The Quantum World) by your discussion though, so make sure to finish those before then.

Lauren Huang 1H

Can someone please explain how to do G13? It says: "To prepare a fertilizer solution, a florist dilutes 1.0 L of 0.20 m NH4NO3(aq) by adding 3.0 L of water. The florist then adds 100. mL of the diluted solution to each plant. How many moles of nitrogen atoms will each plant receive? Solve this ...

Lauren Huang 1H

Yea, when I took the online module that had this question, the correct answer was no (there cannot be more than one limiting reactant). This makes sense because if there were two reactants with the same mole ratio, then neither one would limit the other since they were both consumed completely in th...

Lauren Huang 1H

Make sure to double check your answer before you move on! Sometimes I make a couple of arithmetic mistakes without knowing, so make sure you check that both sides have the same number of elements.

Lauren Huang 1H

There are no decimals used in empirical formulas so you would have to divide the moles by the smallest number of moles calculated and round to the nearest whole number. So in this problem, you would use the molar ratio 3 : 4 : 3

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