Hi
I had a few thermodynamics questions on a thread that was locked. The link is here and my questions are directed at the last post.
http://www.physicsforums.com/showthread.php?t=225555
1. Does the author mean that all quasistatic irreversble processes are reversible or if for a quasistatic irreversible process that goes from state 1 to 2, there is actually another way to get from state 1 to 2 reversibly? Is there some kind of proof that this generalization is true as I can't find it in any books?
2. With regards to the proof for work for non-quasistatic systems, does the proof apply to quasistatic irreversible process as well? On page 17 of Anderson's modern compressible flow, he states that only for reversible process does W = integral of pdV. In addition, I thought that equation (5) that T dS >= dQ used to prove W < integral pdv also applies for any irreversible process quasistatic or not?
3. I'm a bit confused here because I always thought that internal energy was a measure of all the microscopic energies which includes kinetic energy (and that kinetic energy directly correlates to the temperature of gas)?
4. I was also wondering for a real gas (intermolecular forces important) or a chemically reacting system, why is internal energy also a function of specific volume and enthalpy a function of pressure while this isn't the case for ideal gas and non-chemical reacting system?
5. How are irreversibilities accounted for in terms of energy balance for closed or open systems? For a closed and insulated piston cylinder and W < integral PdV, does energy balance become something like:
So for closed systems do losses get accounted for in the internal energy of the final state and for steady state open systems does losses get accounted for in the enthalpy terms (assuming adiabatic processes)?
6. Is there an example that shows how heat is process dependent, in all the books I looked through they only give examples for work but just simply state this for heat without examples?
7. What is the difference between equilibrium and steady state in a general thermodynamics sense?
Thanks very much
I had a few thermodynamics questions on a thread that was locked. The link is here and my questions are directed at the last post.
http://www.physicsforums.com/showthread.php?t=225555
Quote:
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Quasistatic irreversible processes can always be realized in a completely reversible way. E.g. in the above case where the entropy of the gas increases due to absorbing heat, the heat can be supplied to the gas by a heat bath and the temperature difference between the heat bath and the gas can be made arbitrarily small. The entropy increase of the heat bath plus the entropy increase of the heat bath is then zero. The entire process is then reversible. |
2. With regards to the proof for work for non-quasistatic systems, does the proof apply to quasistatic irreversible process as well? On page 17 of Anderson's modern compressible flow, he states that only for reversible process does W = integral of pdV. In addition, I thought that equation (5) that T dS >= dQ used to prove W < integral pdv also applies for any irreversible process quasistatic or not?
Quote:
|
An exteme example is free expansion of a gas in avacuum. In that case no work at all is performed, but this process is so violent that you can object by saying that the pressure of the gas is not well defined. But we can perform a free expansion in small steps by moving a piston very fast from one position to a slighly different position, faster than the gas can expand and then fixing the piston in that position. Then what happens is that the gas expands and bumps into the piston in that new position. The P dV term is then equal to the increase in kinetic energy of the gas which comes at the expense of the internal energy, but this kinetic energy gets dissipated after a while, so the internal energy stays the same. |
4. I was also wondering for a real gas (intermolecular forces important) or a chemically reacting system, why is internal energy also a function of specific volume and enthalpy a function of pressure while this isn't the case for ideal gas and non-chemical reacting system?
5. How are irreversibilities accounted for in terms of energy balance for closed or open systems? For a closed and insulated piston cylinder and W < integral PdV, does energy balance become something like:
W = U2 - U1 = integral PdV - loss
So for closed systems do losses get accounted for in the internal energy of the final state and for steady state open systems does losses get accounted for in the enthalpy terms (assuming adiabatic processes)?
6. Is there an example that shows how heat is process dependent, in all the books I looked through they only give examples for work but just simply state this for heat without examples?
7. What is the difference between equilibrium and steady state in a general thermodynamics sense?
Thanks very much