Joule free adiabatic expansion dT=0?

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Discussion Overview

The discussion revolves around the concept of Joule's free adiabatic expansion and whether the temperature change (dT) is zero during such an expansion. Participants explore the implications of adiabatic processes, isothermal conditions, and the behavior of ideal versus real gases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that during an experiment with zero internal energy, an increase in volume and decrease in pressure would imply constant temperature.
  • Another participant counters that this is not guaranteed, noting that adiabatic expansion can occur and heat loss may happen during work done by the gas.
  • A follow-up question asks whether temperature changes when expanding into a vacuum, stating that no work is done and no heat enters the system.
  • It is mentioned that for Joule's experiment, with both work and heat being zero, the change in internal energy was also zero, leading to a temperature change of zero for an ideal gas.
  • A participant introduces the idea that for real gases, the relationship between internal energy and temperature is not as straightforward and varies slightly.
  • Another participant proposes a scenario involving an endothermic chemical reaction and questions whether conducting it adiabatically would result in a temperature drop in the chemical solution.

Areas of Agreement / Disagreement

Participants express differing views on whether temperature remains constant during Joule's free adiabatic expansion, with some asserting that dT is zero for ideal gases while others highlight conditions under which this may not hold true. The discussion remains unresolved regarding the implications for real gases and the proposed chemical reaction scenario.

Contextual Notes

Participants note that the behavior of ideal gases may differ from real gases, and assumptions about internal energy being a function of temperature only apply to ideal gases. The discussion also highlights the complexity of adiabatic processes and the conditions under which temperature changes may occur.

Who May Find This Useful

This discussion may be of interest to students and professionals in physics and chemistry, particularly those exploring thermodynamics, gas behavior, and the implications of adiabatic processes in various contexts.

Outrageous
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In that experiment , the internal energy is zero , volume increase , pressure of system decrease, then temperature will constant ?

Thanks
 
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Nope, not guaranteed. The expansion can also be adiabatic, or heat can even be loss while work is done by the gas.

Only an isothermal expansion guarantees no change in internal energy.
 
greswd said:
Nope, not guaranteed. The expansion can also be adiabatic, or heat can even be loss while work is done by the gas.

Only an isothermal expansion guarantees no change in internal energy.

Then when it expand to vacuum?
No work will be done because the external pressure is zero.
Internal energy will not change as no heat enter, no work done
Will the temperature change ?
 
Outrageous said:
Then when it expand to vacuum?
No work will be done because the external pressure is zero.
Internal energy will not change as no heat enter, no work done
Will the temperature change ?

That depends.

Since w = 0 and q = 0 for the experiment that Joule performed, the change in internal energy U was also 0.
Joule measured the temperature change to also be 0.
The conclusion was that for an ideal gas, the internal energy U is a function of temperature only.

For a real gas, that is no longer true but varies slightly.

Here is some reading for you.
http://www.chem.arizona.edu/~salzmanr/480a/480ants/jadjte/jadjte.html
 
Thank
Then the answer for this thread is dT= 0 for ideal gas.

When a chemical endothermic reaction is carried out, then heat from the surrounding is absorbed , that is why the container of the chemical solution feel cold.
I wondered if I carry out the same experiment adiabatically, will the temperature of chemical solution drop?
 

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