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Why does ITC measure Enthalpy, not Gibbs Energy?

  1. Feb 4, 2014 #1
    Isothermal Titration Calorimetry measures the enthalpy of (e.g.) protein binding by measuring the amount of heat that must be added/removed to a solution in order to perfectly balance the heat generated/released by the gradual introduction of a protein's binding partner. My understanding is that the experiment operates under constant (well, *almost* constant) temperature and pressure. But don't those conditions (constant T, P) mean that ΔG equals the heat generated/released by binding, as opposed to ΔH? How do we know we should use ΔH instead?

    Some references:
    [1] http://antisensescienceblog.wordpre...plained-isothermal-titration-calorimetry-itc/
    [2] http://www.uic.edu/orgs/ctrstbio/manuals/leavitt.pdf
    Last edited: Feb 4, 2014
  2. jcsd
  3. Feb 4, 2014 #2

    Andrew Mason

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    The actual heat flow is the change in enthalpy, ΔH (P being constant). The change in Gibbs free energy, ΔG, is the difference between ΔH and Qrev (the reversible heat flow). The ΔG tells you how close to reversible the reaction is and what direction it will go spontaneously. It is not a measure of the heat flow at constant pressure.

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