# Easy Thermo Question

An Ideal monatomic gas at initial temperature $$T_0$$ (in Kelvins) expands from initial volume $$V_0$$ to volume $$2V_0$$ by each of the 5 processes indicated in the T-V diagram. In which process is the expansion a.)isothermal, b.) isobaric or c.)adiabatic? Explain your answers.
d.) In which process does the entropy of the gas decrease.

So far Ive said that AE is isothermal, initial and final temperatures are the same.

AC is isobaric, Pressure remains constant

AE is adiabatic, no heat flows in or out of the sytem

Is this right?

I dont know what to do for d.)...

#### Attachments

• phys.jpg
39 KB · Views: 323
Last edited:

## Answers and Replies

huh??? Could you restate the question.

wow, sorry. I dont know how that happened? I only hit reply once.

*edit* problem resolved

Is adiabatic expansion a heating or cooling process?

See edited original post and Attachment.

Andrew Mason
Science Advisor
Homework Helper
An Ideal monatomic gas at initial temperature $$T_0$$ (in Kelvins) expands from initial volume $$V_0$$ to volume $$2V_0$$ by each of the 5 processes indicated in the T-V diagram. In which process is the expansion a.)isothermal, b.) isobaric or c.)adiabatic? Explain your answers.
d.) In which process does the entropy of the gas decrease.

So far Ive said that AE is isothermal, initial and final temperatures are the same.

AC is isobaric, Pressure remains constant

AE is adiabatic, no heat flows in or out of the sytem

Is this right?
I can't see your diagram yet, but I expect there are 3 choices: a horizontal line (T = constant), a curve where T/V = constant and a curve that goes below that (lower final T) where $T/V^{\gamma-1}$ = constant. I think you can determine from that whether your answers are right.
I dont know what to do for d.)...
For adiabatic dS = dQ/T = 0. But for the others, which way does the heat flow?

AM

Last edited:
Andrew Mason
Science Advisor
Homework Helper
Now that I see your graphic of the question, you should check your answer to c).

If volume increases and temperature remains constant, dU does not change but the system does work (dW = PdV). So what can you say about dQ? What is the condition for dQ if it is adiabatic?

AM