As described in Problem 9.21, the manufacture of ethanol from corn starch involves fermentation using a yeast that converts sugars from the starch to ethanol and carbon dioxide in a complicated series of reactions. Taking the sugars to be represented by maltose (molecular weight = 342:3 g/mol), the sum of the fermentation reactions can be written as

(a) The heat of combustion of solid maltose has been measured as 5649 kJ/mol. Estimate the standard heat of the fermentation reaction in Equation 1. State any assumptions.

(b) When the system is operated at 85°F, 0.8 kg of yeast is produced for every kg of ethanol formed.

The yeast used in the process has a chemical formula CH_1.8O_0.5N_0.2 and a standard heat of combustion of 23:4 kJ/g. A modification of the fermentation reaction that accounts for the production of yeast and also shows the consumption of added ammonia is

where c, d, e, f , and g are stoichiometric coefficients. Determine the values of the coefficients, estimate the heat of formation of the yeast, and include this result in obtaining a new value for the standard heat of the fermentation reaction of the yeast by Equation 2. State any assumptions.

Transcribed Image Text:

C12H22011(aq) + H2O → 4C2H5OH(aq) + 4CO2(g) (1)