# Homework Help: Thermodynamics Sign Problem

1. Nov 11, 2009

### coookiemonste

1. The problem statement, all variables and given/known data
A gas spontaneously expands into an evacuated container. Indicate whether delta T, delta E, delta H, delta S, q, w, and delta G are positive, negative, or zero.

2. Relevant equations
delta G < 0 (spontaneous)
delta G= delta H - TdeltaS
delta E= q + w
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3. The attempt at a solution
delta T: 0? (Is it wrong to assume this is an isothermal reaction?)
delta E: 0
delta H: -
delta S: +
q: 0
w: 0
delta G: -
Am I correct? And what difference does it make that it is in an evacuated container?

2. Nov 11, 2009

### Mapes

It's not the best approach to assume this is an isothermal process. Can you show that's it's an isothermal process, by assuming ideality and using what you know about the change in energy?

What's your reasoning behind delta H being negative?

3. Nov 11, 2009

### coookiemonste

Hmm. If the gas is considered ideal, delta E would be zero. Since the internal E depends on T, we can assume that this is an isothermal reaction?

Should delta H be + because added heat is needed to make the gas expand?

4. Nov 11, 2009

### Mapes

Agreed.

How is enthalpy defined?

5. Nov 11, 2009

### coookiemonste

Enthalpy is equal to the internal Energy + PV. So is delta H=0?

6. Nov 11, 2009

### Mapes

Yep.

7. Nov 11, 2009

thank you!