Spontaneous Expansion of Gas into Evacuated Container: Thermodynamic Analysis

[coookiemonste]

Homework Statement

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.

Homework Equations

delta G < 0 (spontaneous)
delta G= delta H - TdeltaS
delta E= q + w
[/B]

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?

 

[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?

 

[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?

 

[Mapes]

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?

Agreed.

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

How is enthalpy defined?

 

[coookiemonste]

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

 

[Mapes]

Yep.

 

[coookiemonste]

thank you!