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Test Number 1

Posted: Sat Feb 03, 2018 4:41 pm
by Hailey Johnson
I need someone to explain a concept question from test 1. For the question that asks if heat is being transferred during the expansion of a balloon when temperature is constant I answered that heat wasn't being transferred, but got it wrong. Can someone tell me how heat is being transferred even though the temperature stays the same?

Re: Test Number 1

Posted: Sat Feb 03, 2018 4:48 pm
by Danah Albaaj 1I
The volume of the balloon decreased, which means there was expansion work done. The definition of expansion work is from the change in the volume of the system, which is how we get the equation w = -P∆V

Re: Test Number 1

Posted: Sat Feb 03, 2018 7:11 pm
by Ammar Amjad 1L
Based on what you've said in your post it appears that the system did work; therefore the balloon expanded. Can you post the full question?

Re: Test Number 1

Posted: Sat Feb 03, 2018 7:57 pm
by miznaakbar
The question stated: A balloon filled with gas is expanded to a larger volume and lower pressure while maintaining the same temperature. Answer yes or no if heat is being transferred in the process.

My TA said that you do expansion work against the constant atmospheric pressure, which increases the volume. However, your temperature stays constant, which means that delta U = 0. This means that q = -w, so the heat flows into the system to balance the loss of energy due to work.

Re: Test Number 1

Posted: Sun Feb 04, 2018 2:22 pm
by Yeyang Zu 2J
you can figure it out it two ways
(question:A balloon filled with gas is expanded to a larger volume and lower pressure while maintaining the same temperature. Answer yes or no if heat is being transferred in the process. )

1:since it is a isothermal expansion, delta T=0, then delta U=0. there is not energy transferred.
2:since temperature stays the same, there is no temperature between difference outside and inside, no heat is transferred.

Re: Test Number 1

Posted: Sun Feb 04, 2018 5:47 pm
by Christina Bedrosian 1B
doing work while maintaining a constant temp needs to include a heat transfer in order to maintain the constant temperature (q=-w or w=-q)

Re: Test Number 1

Posted: Sun Feb 04, 2018 6:09 pm
by Peri Bingham 1G
Heat transfer does not necessarily imply that there is a change in temperature. The heat transfer is due to the work being done by the system.

Re: Test Number 1

Posted: Sun Feb 04, 2018 6:22 pm
by Rachel Formaker 1E
There is heat transferred in this situation in order to keep temperature constant.
As a gas expands, it cools. Because the question tells us that temperature is constant, the gas must have absorbed heat from the surroundings to maintain its temperature and counteract the cooling from expansion.

Re: Test Number 1

Posted: Sun Feb 04, 2018 7:07 pm
by Bansi Amin 1D
So the heat was transferred to make up for the change in energy in the system?

Re: Test Number 1

Posted: Mon Feb 05, 2018 12:39 pm
by Wenjie Dong 2E
Bansi Amin 1D wrote:So the heat was transferred to make up for the change in energy in the system?

Heat is transferred because of a temperature different. The work is done by the system through giving off heat and the work is done to the system by increasing its heat.