Chem Lab C

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Chem Lab C

Postby g-omal » November 9th, 2017, 6:13 am

Consider a Carnot engine (an insulated cylinder with a piston filled with a gas). Why must the cylinder expand during the isothermal phase of the Carnot cycle in which heat flows into the cylinder from a heat source?

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Re: Chem Lab B/C

Postby Nerd_Bunny » January 10th, 2018, 1:19 pm

Seeing as no one has posted here in a while, I'll re-start this.

What are london dispersion forces, and where are they found?
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Re: Chem Lab B/C

Postby dxu46 » January 20th, 2018, 8:29 am

Isn't this only a C event?

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Re: Chemistry Lab C

Postby Tailsfan101 » January 20th, 2018, 8:30 am

dxu46 wrote:Isn't this only a C event?

Be confident in your answers. Say it like this: "This is a C only event."
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Re: Chem Lab B/C

Postby Sleepy » January 20th, 2018, 6:33 pm

Nerd_Bunny wrote:What are london dispersion forces, and where are they found?


Answer
London dispersion forces are weak intermolecular forces that form when electrons in two adjacent atoms align in such a way that temporary dipole moments form. They are present between all molecules, but are stronger when the molecules have high polarization.
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Re: Chem Lab B/C

Postby Nerd_Bunny » January 20th, 2018, 6:44 pm

Sleepy wrote:
Nerd_Bunny wrote:What are london dispersion forces, and where are they found?


Answer
London dispersion forces are weak intermolecular forces that form when electrons in two adjacent atoms align in such a way that temporary dipole moments form. They are present between all molecules, but are stronger when the molecules have high polarization.

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Re: Chem Lab B/C

Postby Sleepy » January 20th, 2018, 6:57 pm

Nerd_Bunny wrote:Correct! Your turn.


Q: Name all intermolecular interactions in ammonia (NH3).
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Re: Chem Lab C

Postby UTF-8 U+6211 U+662F » February 9th, 2018, 5:40 pm

(Just to clarify, yes, this is only a C event)

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Re: Chem Lab B/C

Postby Tesel » February 13th, 2018, 6:15 am

Sleepy wrote:Q: Name all intermolecular interactions in ammonia (NH3).


LDFs - occur in all materials.
Dipole interactions - occur because of the partial negative on the lone electron pair and the partial positive on the hydrogen atoms.
Hydrogen bonds - occur specifically because of the N-H bond, special type of dipole interaction.
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Re: Chem Lab B/C

Postby Sleepy » February 14th, 2018, 12:36 pm

Tesel wrote:
Sleepy wrote:Q: Name all intermolecular interactions in ammonia (NH3).


LDFs - occur in all materials.
Dipole interactions - occur because of the partial negative on the lone electron pair and the partial positive on the hydrogen atoms.
Hydrogen bonds - occur specifically because of the N-H bond, special type of dipole interaction.

Correct!
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Dynamic: 1 | 2 | -
Remote: 2 | 1 | -
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Re: Chem Lab B/C

Postby Tesel » February 14th, 2018, 4:46 pm

What is the specific heat capacity of an ideal gas? Express this value using variables from this equation: PV=m/(mm)RT. Good luck ;)
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Re: Chem Lab B/C

Postby dmis » February 18th, 2018, 9:13 pm

This question was on an invitational test: and I am pretty confident though my answer was marked wrong. What do you think:

As a substance undergoes a change from the solid to the liquid phase at constant temperature the average
kinetic energy of its molecules
a) decreases
b) increases
c) remains the same

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Re: Chem Lab B/C

Postby g-omal » February 19th, 2018, 2:13 pm

Answer:
C. Temperature is constant during a phase change and is proportional to average kinetic energy of the particles.


dmis wrote:This question was on an invitational test: and I am pretty confident though my answer was marked wrong. What do you think:

As a substance undergoes a change from the solid to the liquid phase at constant temperature the average
kinetic energy of its molecules
a) decreases
b) increases
c) remains the same

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Re: Chem Lab B/C

Postby g-omal » February 19th, 2018, 2:33 pm

Answer:
Assuming we're talking about a monatomic ideal gas, you can use Cv = 3/2R and Cp = Cv + R. These come by setting U=3/2nRT equal to Q=nCvT in an isovolumetric process. Going way back, the 3/2 comes from some pretty neat degrees of freedom stuff, but I'm not exactly sure how far I should be going down this deriving rabbit hole.


Tesel wrote:What is the specific heat capacity of an ideal gas? Express this value using variables from this equation: PV=m/(mm)RT. Good luck ;)

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Re: Chem Lab C

Postby Tesel » February 19th, 2018, 6:10 pm

I'd say that's far enough, I should have worded it better, but the main thing was Cv=3/2R.
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