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Enthalpy is useless?

  1. Nov 8, 2011 #1
    So in a constant pressure system if u = q + pv and h = u - pv that means h = q then whats the importance of enthalpy. Why do they say the enthalpy of the reaction is blah blah instead of the heat released or absorbed is blah blah.
  2. jcsd
  3. Nov 8, 2011 #2
    Because enthalpy is a function of state and heat a process function. In case of constant pressure the change of enthalpy is equal to the heat but as soon as the pressure is not constant the values my be different. The change of enthalpy depends on the initial and final state of the system only but heat depends on the path between these states.
  4. Nov 8, 2011 #3

    Simon Bridge

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    Yep - enthalpy is general.
    Remember, the idea is not just to describe specific situations but to come up with something that describes many situations in one go.
  5. Nov 8, 2011 #4
    enthalpy is the total energy of a body of certain volume V, with pressure P on the object to make a room for itself in the surrounding and the work required is PV. So total energy comes out to be U+PV , which is enthalpy (H), and U internal energy.
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