Difference between Isothermal and Adiabatic?

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Discussion Overview

The discussion revolves around the differences between isothermal and adiabatic processes in thermodynamics, focusing on the implications of temperature changes, heat transfer, and work done by or on a gas. Participants seek clarification on how these processes relate to internal energy and temperature changes.

Discussion Character

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

Main Points Raised

  • One participant notes that in isothermal processes, the temperature remains constant, leading to a change in internal energy (ΔU) of zero, yet questions how heat (Q) can change without a temperature difference.
  • Another participant suggests that the work done by or on the gas may be relevant to understanding the processes.
  • A participant expresses confusion about the relationship between heat transfer and temperature change, particularly in adiabatic processes where heat transfer is zero, yet a temperature change occurs.
  • It is mentioned that for an ideal gas, a change in internal energy is associated with work done on the system, even in the absence of heat transfer.
  • One participant references the first law of thermodynamics, indicating that both heat and work can influence internal energy and temperature changes.
  • Historical context is provided by mentioning Joule's experiments, which demonstrated that mechanical work can increase the temperature of a liquid, suggesting a connection between work and internal energy changes.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and confusion regarding the concepts, indicating that there is no consensus on the relationships between heat, work, and temperature changes in isothermal and adiabatic processes.

Contextual Notes

Participants highlight limitations in their understanding, particularly regarding the conditions under which heat and work affect internal energy and temperature, as well as the implications of the first law of thermodynamics.

Saippo
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So for Isothermal, there is no change of T so hence delta U is 0. However, if there isn't a change of temperature, how is there a change of Q? I thought heat was the flow of energy of different temperatures. This confuses me for adiabatic as well. With no heat, how is there a temperature change. Also, apparently adiabatic processes, the change of temperature must be negative. However, why? For a second, I thought it may be because there's no added heat but there shouldn't be heat leaving either.
I feel like this is all tangled up in my head and I would appreciate some clarification!
 
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Do you think that work being done by the gas or on the gas has anything to do with this?
 
I did think about that. So if Q is 0 all the internal energy would go to work. However, I thought temperature change was required for there to be a change of internal energy. Then, I ended up back to, how is there no heat when there is a temperature change when heat is involved when there's a change of temperature. Even if I think that all the energy went to work, because of what I believed in the previous statement, it doesn't make sense to me.
 
Saippo said:
I did think about that. So if Q is 0 all the internal energy would go to work. However, I thought temperature change was required for there to be a change of internal energy.
Yes. That's correct for an ideal gas.
Then, I ended up back to, how is there no heat when there is a temperature change when heat is involved when there's a change of temperature. Even if I think that all the energy went to work, because of what I believed in the previous statement, it doesn't make sense to me.
Heat is not the only thing that can cause a change in internal energy and, along with it, a temperature change. Work can also cause a change in internal energy (even without heat), and, along with it, a temperature change. This is the whole idea behind the first law of thermodynamics ##\Delta U=Q-W##, which is basically a statement of conservation of energy. Both Q (heat) and W (work) can cause the internal energy (and temperature) to change. Joule proved this experimentally when he did mechanical work on a liquid and its temperature increased. This basically showed that doing work on a system is equivalent to adding heat to the system.
 

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