Isothermal Expansion: Work and Heat

In summary: Yeah, that's what I meant to say. The isobaric path has more area and represents more work. So A and B only is the correct answer. In summary, A and B only are the true statements about isothermal expansion. Heat is converted completely into work during isothermal expansion and isothermal expansion can be reversed under ideal conditions.
  • #1
minidee
21
0
Which of the following statements are true?

1. Heat is converted completely into work during isothermal expansion.
2. Isothermal expansion is reversible under ideal conditions.
3. During the process of isothermal expansion, the gas does more work than during the isobaric expansion (at constant pressure) between the same initial and final volumes.

Carefully consider all options and choose the best one.

A only
B only
C only
A and B only
A and C only
B and C only
A and B and C

I can't seem to figure this one out. I think the answer is A only because that definitely works. I'm very unsure about the other two statements though. I believe B is incorrect because only adiabatic processes are reversible. And I believe C can be correct or incorrect based on the situation so I pick A.

Thanks for the help guys!
 
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  • #2
minidee said:
Which of the following statements are true?

1. Heat is converted completely into work during isothermal expansion.
2. Isothermal expansion is reversible under ideal conditions.
3. During the process of isothermal expansion, the gas does more work than during the isobaric expansion (at constant pressure) between the same initial and final volumes.

Carefully consider all options and choose the best one.

A only
B only
C only
A and B only
A and C only
B and C only
A and B and C

I can't seem to figure this one out. I think the answer is A only because that definitely works. I'm very unsure about the other two statements though. I believe B is incorrect because only adiabatic processes are reversible. And I believe C can be correct or incorrect based on the situation so I pick A.

Thanks for the help guys!
For A, apply the first law. What is the change in internal energy in any isothermal change? What does that tell you about the relationship between work and heat flow (W and Q)?

For B, consider the classic four parts of the Carnot engine cycle: is isothermal expansion part of that cycle?

For C, draw a PV diagram for isothermal expansion and for isobaric expansion. Which graph as the most area under it? What does that area represent?

AM
 
  • #3
so I'm guessing that A works because the law applies W=Q.

B actually works because in the carnot engine cycle, isothermal expansion can be reversed.

C, the area represents work. I would say that more work is done on the isobaric.

So A and B only is the correct answer. Am I right?
 
Last edited:
  • #4
i've noticed no one has answered yet. I kind of need this by tonight. thanks!
 
  • #5
minidee said:
so I'm guessing that A works because the law applies W=Q.

B actually works because in the carnot engine cycle, isothermal expansion can be reversed.

C, the area represents work. I would say that more work is done on the isobaric.

So A and B only is the correct answer. Am I right?
You are. But you don't seem very confident. Is the isobaric path above the isothermal? If so, it has more area and represents more work.

AM
 

1. What is isothermal expansion?

Isothermal expansion is a process in thermodynamics where a system undergoes a change in volume without a change in temperature. This means that the heat and work exchanged by the system are equal, resulting in a constant temperature throughout the process.

2. How is work calculated in an isothermal expansion?

In an isothermal expansion, the work done by the system can be calculated using the equation W = PΔV, where P is the pressure and ΔV is the change in volume. This equation holds true because the temperature remains constant, so the work done is equal to the product of pressure and change in volume.

3. What is the relationship between heat and work in an isothermal expansion?

In an isothermal expansion, the heat and work exchanged by the system are equal. This is because the process occurs at a constant temperature, so all the heat energy absorbed by the system is converted into work done by the system. This relationship can be represented by the equation Q = W, where Q is the heat transferred and W is the work done.

4. What are some real-life applications of isothermal expansion?

Isothermal expansion is a common process in refrigerators and heat pumps. In these systems, a compressed gas undergoes an isothermal expansion, resulting in a decrease in temperature. This allows for the transfer of heat from a colder region to a warmer region, thus cooling the desired area.

5. How does isothermal expansion differ from adiabatic expansion?

Isothermal expansion occurs at a constant temperature, while adiabatic expansion occurs without any heat exchange with the surroundings. In an isothermal expansion, the heat and work exchanged are equal, but in an adiabatic expansion, the work done is greater than the heat absorbed by the system. Additionally, the pressure and volume of a gas decrease in an adiabatic expansion, while they remain constant in an isothermal expansion.

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