Thermodynamic processes and the relationships between the quantities they describe

  1. Adiabatic process: a process where no heat is gained or lost. it is my understanding, however, that this is a hypothetical system. There is no insulator on earth good enough to allow this system to exist, except to approximations.

    So, what happens is you have a system where whatever is inside the system is held at the same temperature as the surrounding environment? Is that considered adiabatic?
    Now, what if you add energy to the system, how do you maintain an adiabatic system? Do you alleviate the pressure?

    Isochoric process: a process where the volume doesn't change. no work can be done on an isochoric system because the volume is not allowed to change.

    Is this why the thermodynamic equation describing change in energy cannot be based solely upon work but, rather, it has to include a term for heat transfer?

    Isobaric process: a process where pressure remains constant.

    In reality, is this system only possible if you adjust temperature and volume in equal proportion, so as to avoid increases or decreases in pressure? Is there another scenario where an isobaric process is possible?

    Isothermal process: a process where temperature does not change.

    Does an isothermal system have to be adiabatic? Or does heat flux make the system not adiabatic? In what system do you add energy and keep temperature the same?

    Thank you.
     
  2. jcsd
  3. Re: Thermodynamic processes and the relationships between the quantities they describ

    My you have swallowed the thermodynamic dictionary.

    :smile:

    For any system a state is a condition where the values of certain variables are known (definable).

    We find that we only need a few variables to totally define the state of a system. These are connected by an equation of state such as PV/T = a constant.
    Clearly we only need to know two of these to define the state of a system, as we can calculate the third from this equation.

    Now other equations including other properties are also possible and the first law is about the energy transferred to a system or withdrawn from it.

    So if we have a system at one state (P1 , V1, T1) and we move it to a second state, (P2 , V2, T2) we can achieve this by doing mechanical work on it and/or adding heat energy.

    Adiabatic changes occur when the heat added is zero.
    A good example of an adiabatic change in real life is a sound pressure wave. It is adiabatic because it is so quick thermal energy does not have a chance to transfer.
     
  4. Re: Thermodynamic processes and the relationships between the quantities they describ

    Very interesting. Thank you, very much, for your reply.
     
  5. Chestermiller

    Staff: Mentor

    Re: Thermodynamic processes and the relationships between the quantities they describ

    So what! There is no such thing on earth as an exact right triangle, or an exact equilateral triangle, or any other exact geometric shape. These are all idealizations. This does not prevent you from usefully employing Euclidean geometry to solve practical problems, does it?
     
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