Spontaneous Expansion of Gas into Evacuated Container: Thermodynamic Analysis

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SUMMARY

The discussion centers on the thermodynamic analysis of a gas spontaneously expanding into an evacuated container. Key conclusions include that delta G is negative, indicating spontaneity, while delta E and q are zero, suggesting no change in internal energy or heat exchange. Delta H is debated, with some arguing it should be zero due to the definition of enthalpy, while delta S is positive, reflecting increased disorder. The assumption of isothermal conditions is questioned, emphasizing the need for clarity on temperature changes during the process.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the laws governing spontaneous processes.
  • Familiarity with the concepts of delta G, delta H, delta S, delta E, q, and w.
  • Knowledge of ideal gas behavior and its implications in thermodynamic calculations.
  • Basic grasp of enthalpy and its relationship to internal energy and pressure-volume work.
NEXT STEPS
  • Study the derivation and implications of the Gibbs free energy equation: delta G = delta H - Tdelta S.
  • Explore the conditions under which a process can be considered isothermal and its impact on thermodynamic variables.
  • Investigate the relationship between internal energy and temperature for ideal gases.
  • Review the concept of enthalpy and its calculation in various thermodynamic processes.
USEFUL FOR

This discussion is beneficial for students and professionals in chemistry and physics, particularly those studying thermodynamics, as well as educators seeking to clarify concepts related to gas behavior in evacuated systems.

coookiemonste
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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?
 
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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?
 
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?
 
coookiemonste said:
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.

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

How is enthalpy defined?
 
Enthalpy is equal to the internal Energy + PV. So is delta H=0?
 
Yep.
 
thank you!
 

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