2.10 Entropy change in chemical reactions and the third law(1) S.J.T.0. Phase Transformation and Applications The calculation of entropy changes for a chemical reaction is similar to the calculation in the case of enthalpy changes. One very important difference: Nernst 1906 The entropy change in any chemical reaction involving only pure,crystalline substances: ZERO at the ABSOLUTE Zero of temperature. Pure:pure elements and stoichiometrically balanced compounds that are perfectly crystalline Planck The entropy of a pure,perfectly crystalline substances ZERO at the ABSOLUTE Zero of temperature. Superscript zero:standard state,1 atm △D =0 Subscript zero:temperature ZERO SJTU Thermodynamics of Materials Fall 2012 X.J.Jin Lecture 5 property relationPhase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Fall 2012 © X. J. Jin Lecture 5 property relation 2.10 Entropy change in chemical reactions and the third law (1) The calculation of entropy changes for a chemical reaction is similar to the calculation in the case of enthalpy changes. One very important difference: Nernst 1906 The entropy change in any chemical reaction involving only pure, crystalline substances: ZERO at the ABSOLUTE Zero of temperature. Pure: pure elements and stoichiometrically balanced compounds that are perfectly crystalline. Planck The entropy of a pure, perfectly crystalline substances: ZERO at the ABSOLUTE Zero of temperature. 0 0 ΔS0 = Superscript zero: standard state, 1 atm Subscript zero: temperature ZERO