Understanding 2 Adiabatic Processes and the 2nd Law of Thermodynamics

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Discussion Overview

The discussion revolves around the relationship between adiabatic processes, the second law of thermodynamics, and the definition of heat and temperature. Participants explore whether the second law can be understood without a statistical approach and the implications of heat flow for work in thermodynamic systems.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that the second law of thermodynamics, which relates net work to heat transfer, implies that two adiabatic processes cannot intersect on a PV diagram when connected by an isothermal process.
  • One participant questions whether the second law is merely a restatement of the conservation of energy.
  • Another participant challenges the definition of heat, suggesting that it relies on temperature, which is inherently statistical, thus questioning the validity of the second law without a statistical framework.
  • A different viewpoint suggests that it is possible to explain the necessity of heat flow for work in an engine without resorting to statistical definitions.
  • One participant emphasizes that defining heat requires defining temperature, which involves a statistical understanding of particle interactions, implying that heat cannot be meaningfully discussed without this context.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of a statistical approach to understand heat and the second law of thermodynamics. There is no consensus on whether these concepts can be adequately defined without statistical mechanics.

Contextual Notes

Limitations include the reliance on definitions of heat and temperature, which may not be universally accepted, and the unresolved nature of how adiabatic processes relate to the second law without a statistical framework.

orthovector
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If you accept that the 2nd law of thermo tells you that the

[tex]Work_{net} = Q_{in} - Q_{out}[/tex]

it's easy to see why 2 adiabatic processes cannot cross on a PV diagram when connected by an isothermal process.

however, why is the 2nd law true without taking a statistical approach?
Why must we have heat flow in order to get work out of an engine?
 
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isn't that a restatement of the conservation of energy?
 
how do you define heat? in wikipedia it says "the energy transfer due to a difference in temperature", and temperature is a statistical definition. so there would be no sense to state such a law without the statistical approach.
 
you mean to tell me you cannot explain why 2 adiabatic processes cannot cross without doing a statistical approach to temperature?

I'm sure one can explain why heat flow is necessary for work inside an engine without statistics.

I haven't gotten to statistical and thermal physics yet...
 
no, what I'm telling you is that in order to define heat, you need to define temperature, and temperature is just a way of forgetting about certain degrees of freedom and collapse them into what we call 'temperature'. So to define adiabatic, you need to define heat, so you need to define temperature, and to do this, you collapse this whole mess of particles interacting with each other into one statistical definition, which is i think, the average kinetic energy or something like that.
that is, heat makes no sense at all just like friction makes no sense at all when you are taking into account every degree of freedom your system has.

EDIT: i haven't got to statystical physics yet neither.
 

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