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Clausius clapeyrion equation Hfg

  1. Nov 26, 2011 #1
    Hi guys

    I'm trying to figure out a way of calculating the enthalpy of vaporisation using the clapeyron equation.

    So far I have two different forms of the clapeyron equation. However, I'm not sure how to go any further.

    Ln(P2/P1) = (ΔHfg / R) ( 1/T1 - 1/T2) eqn(1)

    Ln(P) = -(ΔHfg / R) (1/T) + C eqn(2)

    Both of these will give the value of delta Hfg between two T's and P's. Whereas I want a particular value of Hfg at a given T and P. Is this possible?

    Also from eqn (2), which is from the eqn of a straight line, give the gradient of the line to be (-Hfg/R). but surely Hfg isn't constant ?

    i would have though Hfg decreases as T increases.

    Anyway, the point of my question is to see how I can calculate Hfg NOT ΔHfg. I really hope this is possible?

    Thanks very much in advance

    kind Regards
  2. jcsd
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