Question

2.1 Consider the equilibrium between solid nickel carbon monoxide, and nickel tetracarbonyl: Ni (s) + 4C0(g)-→ Ni (CO)4 (g) For the reaction as written, the standard Gibbs free-energy change at 100°C is 1292 cal/mol when the following standard states are used: Ni(s) pure crystalline solid at 100 C under its own vapor pressure CO(g) pure gas at 100°C, unit fugacity Ni(CO)4 (g) pure gas at 100°C, unit fugacity (a) If a vessel is initially charged with pure Ni(CO), and maintained at a temperature of 100 C by immersion in a container of boiling water, what fraction of the Ni(CO)s will decompose if the total pressure in the vessel is main tained constant at 2 atm? Ni(CO)4 2 atmospheres INENN 100°C The vapor pressure of pure nickel a 100°C is 1.23 × 10-46 atm. For purposes of this problem you may assume that the gaseous mixture behaves as an ideal gas. State explicitly any other assumptions that you make. (b) What pressure would be necessary to cause 95% of the Ni(CO), to decompose? Assume that all other conditions are the same as in part (a).

Answer 1

Phase � I Gibbs free energy related to the equilibrium constant by the following relation delta G = -RT ln K The equilibrium constant K can be determined R = 1.987 Kal/K-mol T = 373.15 K G = 1292 cal/mol ln k = 1292/(373.15 times 1.987) = 1.742 K = 5.7 now the reaction occurs like [Ni(Co)_4] ... greaterthan Ni + 4 Co K = [N] [Co]^4/[Ni[Co]_4] Assuming only 1 mol of [Ni(Co)_4] is charged K = e^5/(1-e) e = 8976 = 89.76% decompositions. Part-B: For 95% conversion the value of K = 15.47 DG = 2030.75 cal/mol the pressure required is directly proportional to the no of moles of Ni formed Hence , 2.13 atm pressure is needed for 95% decomposition.