## Thermodynamics B/C

Test your knowledge of various Science Olympiad events.
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### Re: Thermodynamics B/C

Yes, except transfer of heat into the water and not out of the rod and also only two sigfigs. Your turn!

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### Re: Thermodynamics B/C

Yes, except transfer of heat into the water and not out of the rod and also only two sigfigs. Your turn!
You fill a container with 3.5 L of water at an initial temperature of 90 °C. After 1 hour of cooling, you measure the temperature the temperature of the water to have dropped to 65 °C. Lastly, the surrounding temperature of the container remained at a steady 24 °C throughout the entire cooling process. Calculate the change in entropy for the entire system (including both the water and the surroundings).
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Yes, except transfer of heat into the water and not out of the rod and also only two sigfigs. Your turn!
You fill a container with 3.5 L of water at an initial temperature of 90 °C. After 1 hour of cooling, you measure the temperature the temperature of the water to have dropped to 65 °C. Lastly, the surrounding temperature of the container remained at a steady 24 °C throughout the entire cooling process. Calculate the change in entropy for the entire system (including both the water and the surroundings).
P.S. is there a better way to format the equations than having a separate $[math]$ tag every line?

Justin72835
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### Re: Thermodynamics B/C

P.S. is there a better way to format the equations than having a separate tag ---- every line?
Hmm I got 187 J/K as my answer when I did it. I think the fourth line should be

$T(Q) = 363.15 K - \frac{Q}{14360 J/K}$

with a minus instead of a plus. If it were plus, then you would see your temperature increasing (since Q is always positive) instead of decreasing. I redid your work with this correction and I got the same answer. What do you think?

Also, we'll have to make do with putting the math tag before every equation
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Hmm I got 187 J/K as my answer when I did it. I think the fourth line should be

$T(Q) = 363.15 K - \frac{Q}{14360 J/K}$

with a minus instead of a plus. If it were plus, then you would see your temperature increasing (since Q is always positive) instead of decreasing. I redid your work with this correction and I got the same answer. What do you think?
Yeah, that's my bad.
EDIT: Oh yeah, next question. An 10g iron rod at 50 degrees Celsius is dropped into a 1L beaker of water at 60 degrees Celsius. How does the length of the rod change? Use the values of c = 0.50 J/(g*K) for iron and c = 4.0 J/(g*K) for water. Use as many sigfigs as you want.

Justin72835
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### Re: Thermodynamics B/C

Hmm I got 187 J/K as my answer when I did it. I think the fourth line should be

$T(Q) = 363.15 K - \frac{Q}{14360 J/K}$

with a minus instead of a plus. If it were plus, then you would see your temperature increasing (since Q is always positive) instead of decreasing. I redid your work with this correction and I got the same answer. What do you think?
Yeah, that's my bad.
EDIT: Oh yeah, next question. An 10g iron rod at 50 degrees Celsius is dropped into a 1L beaker of water at 60 degrees Celsius. How does the length of the rod change? Use the values of c = 0.50 J/(g*K) for iron and c = 4.0 J/(g*K) for water. Use as many sigfigs as you want.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Correct (as far as I know). Your turn!

Justin72835
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### Re: Thermodynamics B/C

Correct (as far as I know). Your turn!
Alright this question has two parts. The chemical compound ethanol has an enthalpy of combustion of -1360 kJ/mol. You have a piston that can expand and contract. Assume that the lid of the piston is massless and the gas has a pressure of 1 atm. There are 5.2 moles of ideal gas in the piston at 730 K, and you apply enough heat such that the gas expands isothermally until its pressure is only 60% of the original pressure.

1. How much work was done by the gas?

2. Assuming that the heat was added to the gas during this process was formed from the combustion of ethanol, find the number of moles of ethanol used in the reaction.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Alright this question has two parts. The chemical compound ethanol has an enthalpy of combustion of -1360 kJ/mol. You have a piston that can expand and contract. Assume that the lid of the piston is massless and the gas has a pressure of 1 atm. There are 5.2 moles of ideal gas in the piston at 730 K, and you apply enough heat such that the gas expands isothermally until its pressure is only 60% of the original pressure.

1. How much work was done by the gas?

2. Assuming that the heat was added to the gas during this process was formed from the combustion of ethanol, find the number of moles of ethanol used in the reaction.
P.S. Is it just me or should we have an tag?

Justin72835
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### Re: Thermodynamics B/C

P.S. Is it just me or should we have an tag?
Yup that answer is correct! Also, I agree that there should be a specific tag for question marathons. Your turn!
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### Re: Thermodynamics B/C

What is the heat capacity of 50 kg of $H_2O$ at 0 K? What is the heat capacity of 50 kg of $H_2O$ at 273.15 K?

Justin72835
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### Re: Thermodynamics B/C

What is the heat capacity of 50 kg of $H_2O$ at 0 K? What is the heat capacity of 50 kg of $H_2O$ at 273.15 K?
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

What is the heat capacity of 50 kg of $H_2O$ at 0 K? What is the heat capacity of 50 kg of $H_2O$ at 273.15 K?
Not quite...
You can go though

Justin72835
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### Re: Thermodynamics B/C

What is the heat capacity of 50 kg of $H_2O$ at 0 K? What is the heat capacity of 50 kg of $H_2O$ at 273.15 K?
Not quite...
You can go though
I guess I still have a bit of studying to do

You have a room with dimensions 4 meter by 13 meters by 9 meters. The room is filled with 46 kg of an ideal gas which is at a temperature of 22 °C. After pumping out some air, you find that the pressure of the room dropped by half and the temperature of the room dropped by 13 °C.

Find the mass of the air pumped out of the room.
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

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### Re: Thermodynamics B/C

Not quite...
You can go though
I guess I still have a bit of studying to do

You have a room with dimensions 4 meter by 13 meters by 9 meters. The room is filled with 46 kg of an ideal gas which is at a temperature of 22 °C. After pumping out some air, you find that the pressure of the room dropped by half and the temperature of the room dropped by 13 °C.

Find the mass of the air pumped out of the room.