Temperature of iron and wood

  1. If I put an iron of 350K and a wood of 300K in contact, then put them in a container so that they are adiabatic. The question : after a very long time will they become thermal equilibrium? same temperature?
    My guess : they should be same. But they have different specific heat capacities. If the specific heat capacity of wood is larger . Then in order to achieve same temperature, a lot of heat will flow to the wood.
    (a bit not logic) when they are in thermal equilibrium mean that they have same temperature but the heat energy of wood is higher then iron?

    Thank you
     
  2. jcsd
  3. Borek

    Staff: Mentor

    This is in an isolated container, so thermal equilibrium means "uniform temperature". It never means "uniform energy".
     
  4. But why the energy will not get equilibrium? Isn't the temperature of wood and iron also depend on heat energy inside? Then what makes the energy flow from the iron to wood? Because it is no longer due to concentration of gradient of energy between them?
     
  5. sophiecentaur

    sophiecentaur 14,115
    Science Advisor
    Gold Member

    Temperature is the Mean Kinetic Energy; that is what will reach equilibrium. It's basic thermodynamics. The distribution of other forms of energy will depend upon the specific circumstances.
     
  6. So do you mean the mean kinetic energy of wood atoms and iron atoms will be the same?:smile:
     
  7. A first step towards understanding this (in my opinion) is by learning the concept of enthalpy and, in a later step, entropy. The energy will also reach an equilibrium state, but this does not mean that the equilibrium state is uniform over the different materials.
     
  8. sophiecentaur

    sophiecentaur 14,115
    Science Advisor
    Gold Member

    Hm. As they are solids, there will not be a lot of translational KE in the atoms themselves (by definition?) but there is KE in the free electrons in metals and also the vibrational KE. I realise that a lot of thermodynamic arguments seem to assume we're talking of gases.

    @bigfoot
    I presume you aren't implying a continuous flow of energy, when you say the equilibrium state is not continuous. Can you explain?
     
  9. When the system is in thermodynamic equilibrium, it has reached a steady state and there is no transfer of energy anymore. In this equilibrium, the temperature is the same for both wood and iron. Enthalpy for instance has also reached a constant, steady state value, but it is different (higher) for wood than for iron because of the difference in heat capacity. So there is an enthalpy jump at the interface between the wood and the iron.
     
  10. Borek

    Staff: Mentor

    Lack of transfer of energy doesn't follow from the steady state condition. That's why I signaled "isolated container".
     
  11. sophiecentaur

    sophiecentaur 14,115
    Science Advisor
    Gold Member

    I don't understand that exactly. I think it's the double negative that's throwing me. Equilibrium must mean no energy transfer, surely?
     
  12. Borek

    Staff: Mentor

    No, you can have a steady state with a transport going on. Imagine a rod connecting a heat source and a heat sink - assuming temperatures of the source and the sink are constant temperature gradient in the rod is constant as well. There is a steady state in the rod, but the heat is being transported.
     
  13. I am confused as well, can I ask again when wood and iron reach equilibrium, the temperature will be the same,what makes the temperature same? Is the mean kinetic energy, (3/2)kT?

    Then what is the energy flow out from iron to wood should I call? Heat energy? Or potential energy or total energy ?
     
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