Question
Wed August 24, 2011 By:

explain the intensive and extensive properties? derive an expression for a state function H i.e. dH= dU+p(dV) AND dH=dU+dnRT...

Expert Reply
Wed August 24, 2011
Properties that do not depend on the amount of the matter present are known as INTENSIVE properties.
 Examples are 
  • Color
  • Odor
  • Luster - How shiny a substance is.
  • Malleability - The ability of a substance to be beaten into thin sheets.
  • Ductility - The ability of a substance to be drawn into thin wires.
  • Conductivity - The ability of a substance to allow the flow of energy or electricity.
  • Hardness - How easily a substance can be scratched.
  • Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure.
  • Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure).
  • Density - The mass of a substance divided by its volume
  •  
    Properties that do depend on the amount of matter present are known as EXTENSIVE properties.
    Examples are
    • Mass - A measurement of the amount of matter in a object (grams).
    • Weight - A measurement of the gravitational force of attraction of the earth acting on an object.
    • Volume - A measurement of the amount of space a substance occupies.
    • Length
    The derivation:

      According to the first law, dU = dQ - dW        (for any process, neglecting DKE and DPE)

      or after putting the value of W, dU = dQ - pdV

      Also, we know  H = U + pV therefore dH = dU + pdV + Vdp

      so,  dH = dQ - dW + pdV + Vdp (any process)

      or

      dH = dQ + Vdp (for any quasi-static process)

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