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    When do you the energy balance equation which includes Delta U and when do you use the form with Delta H.
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    (Original post by jonnypdot)
    When do you the energy balance equation which includes Delta U and when do you use the form with Delta H.
    Are you referring to changes in enthalpy \Delta H and internal energy \Delta U?

    If so, you need to know the relation:

    \Delta H = \Delta U + P \Delta V

    If your system experiences a change in volume, consider the change in enthalpy. If not, you only need to consider a change in internal energy.
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    (Original post by pleasedtobeatyou)
    Are you referring to changes in enthalpy \Delta H and internal energy \Delta U?

    If so, you need to know the relation:

    \Delta H = \Delta U + P \Delta V

    If your system experiences a change in volume, consider the change in enthalpy. If not, you only need to consider a change in internal energy.
    change in volume in what sense, a reactor would have a fixed volume. I can see the point you made from the equation you have given.
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    (Original post by jonnypdot)
    change in volume in what sense, a reactor would have a fixed volume. I can see the point you made from the equation you have given.
    Essentially, it's when your system boundary changes. One well-known example is that of a balloon expanding.
 
 
 
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