13ThermoP2 - ENTROPY AND SPONTANEITY EXAMPLES H2O(l(25...

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Bojan Chem 13 ENTROPY AND SPONTANEITY EXAMPLES H 2 O(l) (25°) ! H 2 O(g) " S>0 CaCO 3 (s) ! CaO(s) + CO 2 (g) " S>0 N 2 (g) + 3H 2 (g) ! 2NH 3 (g) " S<0 N 2 (g) + O 2 (g) ! 2NO(g) " S>0, but small Mg(s) + Cl 2 (g) ! MgCl 2 (s) " S<0 Ag + (aq) + Cl # (aq) ! AgCl(s) " S<0 Bojan Chem 13 CRITERIA FOR SPONTANEITY " H Exothermic reactions ( " H <0) are usually spontaneous. " S Spontaneous if " S system + " S surroundings > 0 We need a new state function that can predict spontaneity. This is called the Free Energy : " G = " H # T " S T is absolute temperature (in K). " G refers to a reaction at constant T and P. " G < 0 Spontaneous " G > 0 Not spontaneous " G = 0 System at equilibrium.
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Bojan Chem 13 Gibb’s Free Energy Bojan Chem 13 2C 8 H 18 + 25O 2 ! 16CO 2 + 18H 2 O Burning of gasoline " H o " S o CaCO 3 (s) ! CaO (s) + CO 2 (g) " H o " S o 2 H 2 (g) + O 2 (g) ! 2H 2 O (g) " H o " S o N 2 (g) + 3Cl 2 (g) ! 2NCl 3 (g) " H o " S o Will it go?
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Bojan Chem 13 " G = " H # T " S " H and " S do not change
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This note was uploaded on 07/23/2008 for the course CHEM 112 taught by Professor Vandersluys,lorschmid,kylem during the Fall '07 term at Penn State.

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13ThermoP2 - ENTROPY AND SPONTANEITY EXAMPLES H2O(l(25...

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