1.) Predict whether the entropy change for each of the following reactions will have a positive value or a negative value. (a) CH3CO2H (g) → CO2 (g) + CH4 (g) (b) CO (g) + 3 H2 (g) → CH4 (g) + H2O (g) (c) 2 Cr (s) + 6 HCl (g) → 2 CrCl3 (s) + 3 H2 (g)
2.) Calculate the entropy change at 25°C for the following reaction: 2 C (s,graphite) + 3 H2 (g) → C2H6 (g). The entropy contents of the reactants and product at 25°C are as follows: Substance S, J/mol•K C (s,graphite) 5.74 H2 (g) 130.68 C2H6 (g) 229.6
3.) (a) Use the data given below and calculate ?Ho, ?So, ?Go, and Kp at 25° C for the reaction: C2H5OH (g) → C2H4 (g) + H2O (g) (b) Calculate ?G for the reaction at 250 °C. (c) At what temperature (°C) is ?G equal to zero? In what temperature range is this reaction productfavored? Compound ? H o , kJ/mol S o , J/mol • K C2H5OH (g) -235.1 282.7 C2H4 (g) 52.26 219.56 H2O (g) -241.82 188.83
4.) Classify each of the following reactions as one of these four types: • spontaneous at all temperatures • not spontaneous at any temperature • spontaneous below a certain temperature but not above • spontaneous above a certain temperature but not below .
(a) CaS (s) + H2S (g) → CaH2 (s) + 2 S (s); ?H = 317 kJ; ?S = -157 J/K (b) C2H5OH (g) → C2H4 (g) + H2O (g); ?H = 45.5 kJ; ?S = 125.7 J/K (c) KClO3 (s) + S (s) → KCl (s) + SO3 (g); ?H = -435 kJ; ?S = 164 J/K (d) N2 (g) + 3 H2 (g) → 2 NH3 (g); ?H = -92.2 kJ; ?S = -198.8 J/K