5 pts d Is the above reaction spontaneous at 25 o C 7 A reaction has the

# 5 pts d is the above reaction spontaneous at 25 o c 7

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(5 pts) d) Is the above reaction spontaneous at 25 o C?
7. A reaction has the following thermodynamic data: H o S o - 10000 J mol -1 -25 J mol -1 K -1 (5 pts) a) Calculate G o for this reaction at 25 o C. (5 pts) b) Is the reaction spontaneous at 25 o C? (5 pts) c) Is the reaction spontaneous at 200 o C? (5 pts) d) What is the temperature at which the reaction is just as likely to be spontaneous in the forward direction as in the reverse direction?
Formulae you might need to know: S= k x ln (W) q = n x H phase change S (p≠1bar) = S o – R ln(p) S (c≠1M) = S o – R ln(c) S = q t /T S o rxn = Σ coeff products x S o products Σ coeff reactants x S o reactants ∆Η o rxn = Σ coeff products x H f o products Σ coeff reactants x H f o reactants G o rxn = Σ coeff products x G f o products Σ coeff reactants x G f o reactants G o = ∆Η o – T x S o G o rxn,T ~ ∆Η o rxn,298K – T x S o rxn, 298K Constants and other info you might need to know: 1 atm = 1.01325 Bar H solidification water = - 6.01 kJ mol -1 R = 8.314 J mol -1 K -1 k (Boltzmann’s constant) = 1.381 x 10 -23 J K -1 H o f (kJ mol -1 ) S o (J mol -1 K -1 ) H 2 O (l) -285.8 70.0 NH 3 (g) -45.9 192.8 O 2 (g) 0 205.15 C 3 H 6 (g) 20.0 226.9 C 3 H 3 N (l) 172.9 188 H 2 O (g) -241.8 188.8
Answers 1. In any spontaneous process, the total entropy increases, i.e. S total > 0 2. a) ii b) S = k lnW S = 9.6 x 10 -24 J/K 3. +11 J/K 4. A pure, perfect crystal at 0 K has zero entropy; or S (pure, perfect crystal; T=0K) = 0 5. a) 185.9 J mol -1 K -1 b) 1.93 J K -1 6. a) -0.659 kJ/K b) -1317 kJ c) -1121 kJ d) Yes 7. a) -2550 J b) Yes c) No d) 400 K

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• Spring '08
• SHUMAN