2.10 Entropy change in chemical reactions and the third law(1) S.J.T.U. 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. AS8=0 Superscript zero:standard state,1 atm Subscript zero:temperature ZERO SJTU Physical Chemistry of Materials Spring 2010 ©X.J.Jin Lecture 5 property relation IPhase Transformation and Applications S. J. T. U. SJTU Physical Chemistry of Materials Spring 2010 © X. J. Jin Lecture 5 property relation I 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 S0  Superscript zero: standard state, 1 atm Subscript zero: temperature ZERO