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Difference between Enthalpy and Heat

  1. Dec 15, 2009 #1
    I searched this on google but I couldn't find anything. Is enthalpy the same thing as heat? There is a formula, q=m[tex]\Delta[/tex]H, so it seems like they should be different, but from what I've learned H just seems like heat to me... Also, if q=ms[tex]\Delta[/tex]T and q=m[tex]\Delta[/tex]H, then does ms[tex]\Delta[/tex]T=m[tex]\Delta[/tex] so [tex]\Delta[/tex]H=s[tex]\Delta[/tex]T?
     
  2. jcsd
  3. Dec 15, 2009 #2
    They're very closely related. One way to think of it is that enthalpy is a specific type of heat, given by the energy released (or absorbed) by the breaking/formation of chemical bonds. I'm sure someone else can expand on this; I don't want to get into a ton of detail on it just because, well, I don't know a ton of details on it.
     
  4. Dec 15, 2009 #3
    Are you sure q = delta H.m and q = mS delta T are correct ?
    What I learned is delta H = T.delta S + delta G
     
  5. Dec 16, 2009 #4

    DrDu

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    Enthalpy is a function of state, heat isn't. Hence they cannot be the same in general.
    Enthalpy is only equal to heat in reversible isobaric reactions if the only work done is volume work (-p Delta V). E.g. if energy is supplied by an electric current, this will change enthalpy but not necessarily lead to a heat flow. Often, reversibility is not crucial as long as the work done to the system is still (-p Delta V). It is clear that this won't hold e.g. in an explosion, when a piston moves so rapidly that shock waves are formed.
     
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