Chem208_Lecture_21_Color

Chem208_Lecture_21_Color - Today Thermodynamics(Chapter 19...

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Unformatted text preview: Today: Thermodynamics (Chapter 19) Chapters 15–18, 24 Exam coverage: PS9 will go out in lecture on Thursday Exam II: Tonight, 7:30-9:00 Room Assignments are shown on last Tuesday’s handout 1 Spontaneous Changes A spontaneous change is a change that, once begun, has a tendency to occur without being driven by an external influence. A spontaneous change does not necessarily occur rapidly. 2 Thermodynamics What determines whether a process will proceed spontaneously? 2 H2(g) + O2(g) ⇔ 2 H20(i) or 2 H2O(l) ⇔ 2 H2(g) + O2(g) H2O(l) ⇔ H20(s) or H2O(s) ⇔ H20(l) 3 Natural Pattern • Energy and matter tend to become more disordered (or random) • The quantitative measure of this disorder or randomness is known as Entropy 4 Second Law of Thermodynamics The entropy of the universe increases in the course of a spontaneous change. or The entropy of an isolated system increases in the course of a spontaneous change. Isolated System: no interactions with surroundings 5 Statistical View of Entropy Boltzmann: S = k lnW k: Boltzmann constant; k = 1.38 x 10-23 J/K (R = NAk) W: # of microstates of the same energy available to the system 6 ∆S = qrev/T or dS = dqrev/T = CpdT/T ∆S = Cp ln (Tf/Ti) 7 Third Law of Thermodynamics The entropy of a pure, perfect crystal at 0 K is zero. Standard Entropy, S°, is the absolute entropy of a substance in its standard state. 8 Calculate ∆S° for the oxidation of NH3(g) by O2(g) to produce NO(g) and H2O(l) 9 ...
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This note was uploaded on 03/29/2009 for the course CHEM 2080 taught by Professor Davis,f during the Spring '07 term at Cornell.

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Chem208_Lecture_21_Color - Today Thermodynamics(Chapter 19...

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