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Why in a reversible adiabatic process you can plot the exact process path in the P-V-T coordinates, but you can't do so under different conditions?
I assume that "under different conditions" refers to a non-reversible adiabatic process. An example of such a process would be a sudden expansion of gas in an insulated container due to a sudden reduction of outside pressure. Such a process is generally thought to be adiabatic since there is no exchange of heat with the surroundings.asdf1 said:Why in a reversible adiabatic process you can plot the exact process path in the P-V-T coordinates, but you can't do so under different conditions?
PV=nRT is a relationship between P, V and T in a gas that is in equilibrium. Suppose you have a can of compressed air and open it up in outer space. [itex]P_0V_0 =nRT_0[/itex] = the energy of the compressed gas, and the gas does no work in a free expansion and no heat is exchanged with the surroundings. Does P'V' (pressure and volume at time t', say) represent the energy of the expanding gas? If so, it must be the same as the original energy: [itex]P'V' = P_0V_0 =nRT_0 = nRT'[/itex]. This would mean that the temperature is constant. Is that true? How do you define the temperature of an expanding gas? What about the translational kinetic energy of the gas molecules? Where does that fit in to PV=nRT?asdf1 said:I thought that PV=nRT is true no matter what for ideal gases. Why can't it be true if the system isn't in equilibrium?