CHEMISTRY COMMUNITY

Mariane Sanchez 1E

I'm still uncertain when to use Cv or Cp in finding the entropy. I've seen some threads saying that they will explicitly say which variable is constant in the question. But im looking at question 2part B on the winter 2014 Final where the volumes are changing, yet they still used Cv?

Mariane Sanchez 1E

In the equation sheet in the test they use E= standard E - 0.05916/n(logQ). But in some cases ive seen the numerator to be 0.0257. Is there a difference between the two?

Mariane Sanchez 1E

The question says: Suppose that each of the following pairs of redox couples is joined to form a galvanic cell that generates a current under standard conditions. Identify the oxidizing agent and the reducing agent, write a cell diagram, and 2 calculate the standard cell potential. (a) Co /Co and Ti...

Mariane Sanchez 1E

The question says: one step in the production of hydrogen as fuel is the reaction of methane with water vapor: CH4(g)+H2O(g) --> CO2(g)+3H2(g). deltaH=-318KJ. What is the change in internal energy for the production of 1.00 mol H2? I understand that the formula delta U= delta H - P delta V must be u...

Mariane Sanchez 1E

OMG lol I meant question #115 on chapter 14.

Mariane Sanchez 1E

How did they come up with the half reactions in the solutions manual?

Mariane Sanchez 1E

Q: What is "HIJKLMNO"?
A: H2O.

Mariane Sanchez 1E

Q: If H20 is water, what is H204?
A: Drinking, bathing, washing, swimming, etc.

Mariane Sanchez 1E

Anyone know how they got the formula in the solutions manual for #61? Is it somehow related to the slope of an Arrhenius graph?

Mariane Sanchez 1E

Q: What do you do with a sick chemist?
A. First you try to helium, then you try to curium, but if this fails then you have to barium.

Mariane Sanchez 1E

I told a chemistry joke once, but there was no reaction. :(

Mariane Sanchez 1E

The average rate of the reaction N2(g) + 3 H2(g) --> 2 NH3(g) over a certain period is reported as 1.15 (mmol NH3) L -1 h -1. (a) What is the average rate over the same period in terms of the consumption of H2?

Mariane Sanchez 1E

In this example the molarity of the reaction was given as 1.00 mol/L. They want to know what deltaG is. I understand that you can find deltaG with -nFE. My question is how they found the number of mol as 2.00 mol?

Mariane Sanchez 1E

How do you find the oxidation state of an element/molecule? Is it just something you memorize?

Mariane Sanchez 1E

The question says: " Calculate the standard enthalpy of combustion of glucose from the standard enthalpies of formation in Table 8.4 and Appendix 2A." I used the formula standard deltaH= [sigma n(deltaH)formation of products] - [sigma n(deltaH)formation of reactants]. I got the same magnit...

Mariane Sanchez 1E

The question says: " The thermochemical equation for the combustion of cyclohexane, C6H12, is C6H12(l) + 9 O2(g) -> 6 CO2(g) + 6 H2O(l), deltaH = - 3920 kJ at 298 K. What is the change in internal energy for the combustion of 1.00 mol C6H12(l) at 298 K?" I used the formula deltaU= deltaH-d...

Mariane Sanchez 1E

The question says: "Calculate the change in molar entropy of an ideal gas when it is compressed isothermally to one-third its initial volume." They got an answer of 9.13J/K.mol. Can someone please explain how they got that?

Mariane Sanchez 1E

The question says: "The temperature of 5.5 g of stainless steel is increased from 20 C to 100 C. What is the change in the entropy of the stainless steel? The specific heat capacity of stainless steel is 0.51 J /( C)(g)." I'm not entirely sure how to go about this problem, is it okay if I ...

Mariane Sanchez 1E

im still confused as to how reversible and irreversible process work in thermodynamics? can someone please explain the concepts and how they relate with entropy?

Mariane Sanchez 1E

just a bit confused as to why the entropy increases if the heat capacity is greater?

Mariane Sanchez 1E

im running out of chemistry jokes i should zinc of new ones :(

Mariane Sanchez 1E

Neon was cracking up so much he was like
"That was sodium funny. I slapped my neon that one!"

Mariane Sanchez 1E

https://scontent-lax3-1.xx.fbcdn.net/v/t1.0-9/20374483_1249051675203288_1318601126448527178_n.jpg?oh=768d32a3c4a46ac16b00d32b77de6c9d&oe=5B1A921C

Mariane Sanchez 1E

when is the unit for the standard enthalpy of formation just kJ and when is it kJ/mol? i noticed in 8.65 that the reactants and products' enthalpy of formation are in kJ/mol, but the enthalpy for the reaction is just in kJ.

Mariane Sanchez 1E

in 8.57, it says-- Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) + 2 H2(g) --> C2H6(g), from the following data: deltaHc (C2H2, g) =-1300. kJ·mol 1, deltaHc (C2H6, g)=- 1560. kJ·mol 1, deltaHc (H2, g)=- 286 kJ·mol . Can someone explain how to go about this proble...

Mariane Sanchez 1E

A neutron walked into a bar and asked how much for a drink. The bartender replied, "for you, no charge."

Mariane Sanchez 1E

so in lecture today dr. lavelle talked about how you can change the energy of a system if you add or subtract substance from the system. how so?

Mariane Sanchez 1E

why is the standard enthalpy of formation of an element in its most stable form zero? does that mean it doesn't release energy when it is formed?

Mariane Sanchez 1E

so the formula for enthalpy is internal energy + pressure(volume). why is pressure and volume need to be accounted for when calculating enthalpy?

Mariane Sanchez 1E

The optimist sees the glass half full. The pessimist sees the glass half empty. The chemist sees the glass completely full, half with liquid and half with air.

Mariane Sanchez 1E

so i know the hw for this week is on ch 8. but for wk 2 do we answer ch 9 questions? or just the stuff that prof lavelle lectured on?

Mariane Sanchez 1E

The book says: "In chemistry, though, we are more concerned with heat transfers at constant pressure: most chemical reactions take place in containers open to the atmosphere and therefore take place at a constant pressure of about 1 atm. Such systems are free to expand or contract. If a gas is ...

Mariane Sanchez 1E

Hello Dr. Lavelle, Wow! What a quarter! This Chemistry class was definitely a great experience. I never liked Chemistry before because I can never understand it... until I got into your class. It's amazing how one's perspective can instantly change once a great teacher comes along -- and in just a s...

Mariane Sanchez 1E

12.131 Recall from Section 11.13 that hemoglobin (Hb) molecules in blood carry O2 molecules from the lungs, where the concentration of oxygen is high, to the tissues where it is low. In the tissues the equilibrium H3O (aq) + HbO2 (aq) <-> HHb(aq) + H2O(l) + O2(aq) releases oxygen. When muscles work ...

Mariane Sanchez 1E

Why is the Oxygen the central atom when it is more electronegative than Cl?

Mariane Sanchez 1E

Just wanted to make sure if we will be given the formula sheet on the final?

Mariane Sanchez 1E

Hey all, I was reading the chapter and stumbled upon this sentence: "In other words, a Brønsted acid is a supplier of one particular Lewis acid, a proton." can someone please tone it down for me because I am just confused with what the relation between a Bronsted acid and Lewis acid is?

Mariane Sanchez 1E

Q: What do you call a tooth in a glass of water?
A: One molar solution

Mariane Sanchez 1E

Whoops I made a mistake, I thought it was -diamine instead of -triamine. Thank you so much!

Mariane Sanchez 1E

How many binding sites does dien have? Would it be just multiplying 2 by 2 because en has 2 binding sites?

Mariane Sanchez 1E

Q: Why does hamburger yield lower energy than steak?
A: Because it's in the ground state.

Mariane Sanchez 1E

Hey all,

Just a bit confused and can't really wrap my head around the idea that in equilibrium, the reaction will still happen and the concentrations of the products and reactants will be constant? How does that happen?

Mariane Sanchez 1E

is the hw for week 8 on ch 4 or 5?

Mariane Sanchez 1E

"The name's bond. Sigma bond."
-007

Mariane Sanchez 1E

I think this thread might help you guys out. viewtopic.php?f=39&t=23193

Mariane Sanchez 1E

Correct me if I'm wrong but I'm inferring you determine the charge based on how many electrons it needs to take out/it needs to add in order to attain a noble gas electron configuration? So for example for Mg, since it is in the 3rd period s-block, it is easier for it to take out 2 electrons (and th...

Mariane Sanchez 1E

Hey all,

Why is it that there is less energy when atoms are bonded as compared to when they were separated?

Mariane Sanchez 1E

Will there be a review session beside the UA sessions? Like a session wherein it's not just for student questions but also going over all the past topics?

Mariane Sanchez 1E

Hey all,

In which scenario would there be a negative/positive electron affinity? I just can't visualize why there needs to be more energy /release of energy when attaching an electron to an atom.

Mariane Sanchez 1E

Hey all,

So for electron configuration I know we fill in 4s first before 3d. Does that mean that 3d has higher energy level than 4s? If yes/no, please help me understand why/why not. Thanks!

Mariane Sanchez 1E

Hey all, I figured out the first part of the question, but I'm having troubles finding what makes the speed a reasonable amount. 34. If an electron (mass 9.11 x 10-31 kg) has an associated wavelength of 7.28 x 10-9 m, what is its speed? Is your answer reasonable, why? A. 1.00 x 10-5 m.s-1. Yes. 1.00...

Mariane Sanchez 1E

Hi!

So basically what I did here is I divided the Total number of Energy released in 1 sec, which is 11J, by the energy per photon, which is the answer you got from part a. After that, you should get the number of photons.

Mariane Sanchez 1E

Hey all, can someone tell me what the right answer and why fro #24? I tried answering visible light but it was incorrect. Thanks! In photoelectric experiments, typically what part of the electromagnetic spectrum is the incoming light? A. Ultraviolet B. Infrared C. Visible light D. Gamma rays E. None...

Mariane Sanchez 1E

Does anyone know where I can buy a course reader for this class? I already checked the bookstore and it appears that they don't carry it.

Thanks.

Mariane Sanchez 1E

Hi there,

Just wondering if the UA Peer Learning Sessions are specific for Chem 14A students only or are there also students/concepts discussed from higher Chem classes?

Thanks

Mariane Sanchez 1E

Taylor 1F wrote:Also, are we supposed to do the pre-modules for week 2 before next week?

I think the pre-modules are just optional stuff and not graded. :)

Mariane Sanchez 1E

Hi, just wanted some clarification regarding significant figures.
For example the two given numbers for a problem are as follows: 5.43 and 5.9.
How many significant figures should the final answer be in?

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