Thermodynamics Solutions: #30

30.* (1992 3 1) The following polymerization reaction has DH° = -78.58 kJ/mol at room temperature. The equlilibrium constant is 4.3 x 10^-6

A. Is this reaction exothermic or endothermic?

At 25°C, DH°=-78.58 kJ/mol. Therefore, the reaction is exothermic (releases heat).

B. Calculate DG° at 25°C.

C. Calculate DS° at 25°C.

DS° is negative, signifying that the order of the system is increasing. (2 molecules are becoming 1 molecule.)

D. Calculate K at 700°C.

E. Offer an explanation for the different equilibrium constant values at the different temperatures.

The forward reaction is less favored at higher temperature because heat is a product of the exothermic forward reaction. If you add heat you drive the reaction toward the reactants (backwards). This is Le Châtelier's Principle!