Thermodynamics B/C

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Re: Thermodynamics B/C

Postby Justin72835 » March 30th, 2018, 5:40 pm

You have a metal pot with heat capacity 540 J/K at a temperature of 114 °C. You then add 350 mL of water at 23 °C into the pot.

a. Is there any steam produced? (yes or no)

b. If yes, then what is the final temperature of the steam? If no, then what is the equilibrium temperature between the water and the pot?
Assuming the whole pot of water has to get to 100 degrees before any steam is produced:
Energy to heat water + energy to boil water + energy to heat steam = energy lost from metal pot.

=> T = -615 degrees Celsius, which is clearly impossible.


=> T = 47 degrees Celsius

a) No
b) 47 degrees Celsius
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » March 31st, 2018, 6:23 pm

Explain why we can make assumptions in the derivation of the ideal gas law, PV = nRT, such as "The number of molecules moving in each axis (x, y, and z) is equal".

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Re: Thermodynamics B/C

Postby Justin72835 » April 3rd, 2018, 11:35 am

Explain why we can make assumptions in the derivation of the ideal gas law, PV = nRT, such as "The number of molecules moving in each axis (x, y, and z) is equal".
Answer
Not really sure about this one. My answer would be that because the molecules are so small, there are so many of them, and they have relatively little interaction with one another, you can assume that all the molecules follow Newton's Law of Motion and collide elastically with each other. From this, you are able to draw other conclusions as well.
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » April 3rd, 2018, 5:44 pm

Explain why we can make assumptions in the derivation of the ideal gas law, PV = nRT, such as "The number of molecules moving in each axis (x, y, and z) is equal".
Answer
Not really sure about this one. My answer would be that because the molecules are so small, there are so many of them, and they have relatively little interaction with one another, you can assume that all the molecules follow Newton's Law of Motion and collide elastically with each other. From this, you are able to draw other conclusions as well.
Yep, your turn
for the record, I was just looking for there being so many molecules that statistical treatment can be applied to them (especially that they have approximately random motion)

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Re: Thermodynamics B/C

Postby Justin72835 » April 3rd, 2018, 10:26 pm

Two gases occupy two containers, A and B. The gas in A, of volume 0.14 cubic meters, exerts a pressure of 1.18 MPa. The gas in B, of volume 0.21 cubic meters, exerts a pressure of 0.82 MPa. The containers are united by a tube of negligible volume and the gases are allowed to intermingle. What is the final pressure in the container if the temperature remains constant?
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Re: Thermodynamics B/C

Postby MattChina » April 4th, 2018, 7:05 am

Two gases occupy two containers, A and B. The gas in A, of volume 0.14 cubic meters, exerts a pressure of 1.18 MPa. The gas in B, of volume 0.21 cubic meters, exerts a pressure of 0.82 MPa. The containers are united by a tube of negligible volume and the gases are allowed to intermingle. What is the final pressure in the container if the temperature remains constant?
answer
0.964?
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Re: Thermodynamics B/C

Postby Justin72835 » April 4th, 2018, 6:51 pm

Two gases occupy two containers, A and B. The gas in A, of volume 0.14 cubic meters, exerts a pressure of 1.18 MPa. The gas in B, of volume 0.21 cubic meters, exerts a pressure of 0.82 MPa. The containers are united by a tube of negligible volume and the gases are allowed to intermingle. What is the final pressure in the container if the temperature remains constant?
answer
0.964?
Not quite. How did you get your answer?

EDIT: This answer is actually correct.
Last edited by Justin72835 on April 4th, 2018, 7:18 pm, edited 1 time in total.
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » April 4th, 2018, 7:05 pm

Two gases occupy two containers, A and B. The gas in A, of volume 0.14 cubic meters, exerts a pressure of 1.18 MPa. The gas in B, of volume 0.21 cubic meters, exerts a pressure of 0.82 MPa. The containers are united by a tube of negligible volume and the gases are allowed to intermingle. What is the final pressure in the container if the temperature remains constant?
answer
0.964?
Not quite. How did you get your answer?
I got the same answer :/
Using the law of partial pressures 1.18 MPa * (0.14/0.35) + 0.82 MPa * (0.21/0.35) = 0.964 MPa

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Re: Thermodynamics B/C

Postby MattChina » April 4th, 2018, 7:08 pm

Two gases occupy two containers, A and B. The gas in A, of volume 0.14 cubic meters, exerts a pressure of 1.18 MPa. The gas in B, of volume 0.21 cubic meters, exerts a pressure of 0.82 MPa. The containers are united by a tube of negligible volume and the gases are allowed to intermingle. What is the final pressure in the container if the temperature remains constant?
answer
0.964?
Not quite. How did you get your answer?

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Re: Thermodynamics B/C

Postby Justin72835 » April 4th, 2018, 7:22 pm

Nevermind, both of you (UTF-8 U+6211 U+662F and MattChina) are right. I messed up my calculations beforehand :cry:

Anyways, great job to both of you and sorry for the confusion! I think it's MattChina's turn now.
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But in ourselves, that we are underlings."


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Re: Thermodynamics B/C

Postby MattChina » April 4th, 2018, 7:38 pm

Lets do this. What is the best way to increase the efficiency of a carnot engine?
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Re: Thermodynamics B/C

Postby Justin72835 » April 5th, 2018, 4:20 pm

Lets do this. What is the best way to increase the efficiency of a carnot engine?
Answer
[math]e=1-\frac{Tc}{Th}[/math]
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Re: Thermodynamics B/C

Postby UTF-8 U+6211 U+662F » April 6th, 2018, 7:32 pm

Lets do this. What is the best way to increase the efficiency of a carnot engine?
Answer
[math]e=1-\frac{Tc}{Th}[/math]
(i.e.)
Increase the ratio of hot temperature to cold temperature

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Re: Thermodynamics B/C

Postby Justin72835 » April 6th, 2018, 7:40 pm

Lets do this. What is the best way to increase the efficiency of a carnot engine?
Answer
[math]e=1-\frac{Tc}{Th}[/math]
(i.e.)
Increase the ratio of hot temperature to cold temperature
Oh, I completely misread that question. :(
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But in ourselves, that we are underlings."


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Re: Thermodynamics B/C

Postby MattChina » April 7th, 2018, 7:59 am

Lets do this. What is the best way to increase the efficiency of a carnot engine?
Answer
[math]e=1-\frac{Tc}{Th}[/math]
(i.e.)
Increase the ratio of hot temperature to cold temperature
correct. your turn
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