化学原理Chemistry课件-post+9+Thermodynamics介绍.ppt

* * * * Chapter 18 Thermodynamics In this Chapter, we will address several aspects as follows: I) How to predict whether a reaction under a given conditions can occur or not ? II) How to make the reaction happen, if it does not proceed under primary conditions? Spontaneity and Entropy (S). The Second and Third Laws of thermodynamics. Free Energy (G) and Equilibrium (K). Spontaneous process: spontaneous non-spontaneous 18.2 Go ahead by itself, without help from surroundings. spontaneous Non- spontaneous What are the factors controlling the spontaneity? CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) DH0 = -890.4 kJ H+ (aq) + OH- (aq) H2O (l) DH0 = -56.2 kJ H2O (s) H2O (l) DH0 = 6.01 kJ NH4NO3 (s) NH4+(aq) + NO3- (aq) DH0 = 25 kJ H2O Energy Freedom Entropy (S): a measure of system disorder. order S disorder S DS = Sf - Si DS 0 For a given substance: Ssolid Sliquid Sgas H2O (s) H2O (l) DS 0 18.2 Heating hydrogen gas from 600C to 800C Crystallization from a supersaturated solution DS 0 For a process: Entropy is also a State function. E1 H1 S1 E2 H2 S2 n1 P1V1T1 n2 P2V2T2 State 1 State 2 DE = E2 – E1 DH = H2 – H1 DS = S2 – S1 The value of S is only determined by the state, regardless of how the state is reached. How to quantify the Entropy? Microstates W=1 W=4 W=6 S In 1868, Boltzmann proposed S = k ln W DS = Sf - Si For a process: DS = k ln Wf Wi Boltzmann constant k =1.38×10-23 J/K For CH3OH and C2H5OH: Smethanol Sethanol The Second Law of Thermodynamics The entropy of the universe increases in a spontaneous process, and remains unchanged in an equilibrium process. DSuniv = DSsys + DSsurr 0 (1) Spontaneous process: DSuniv = DSsys + DSsurr = 0 (2) Equilibrium process: In order to predict the direction of a chemical reaction, however, both DSsys and DSsurr need to be calculated, which is a question remaining to be solved. How to calculate DSsurr,