CHM 145 Lecture 20: CHM 145 3/16/17
24 Mar 2017
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Document Summary
The temperature dependence of ssurr: the spontaneity of many reactions or processes is temperature-dependent, such processes are either, spontaneous at low t, spontaneous at high t. Consider an isothermal process (a process that takes place at a constant temperature), such as a phase change (e. g. , melting, boiling). Ssurr = sys / t (constant p, t) qsys means the flow of heat as the process is carried out reversibly in very small steps. qsys = sys if the reaction occurs at constant temperature and constant pressure. Remember, spontaneous processes must result in an increase in the entropy of the universe! Example: melting 1 mol of ice at 37 c: step 1: melt the ice at 0 c. Ssys = qsys/t = hfus / t = +6. 01 kj / 273 k. Ssurr = qsys/t = 6. 01 kj / 310 k. Thus, suniv = ssys + ssurr = +22. 0 j/k 19. 4 j/k.
