Question

if C6H12O6 -> 2 C2H5OH + 2 CO2 represents the fermentation of sugar to produce alcohol, and the reaction is only 40.0% efficient (% yield), what is the actual yield of alcohol from 454 g of C6H12O6

Answer 1

Another stoichiometry problem but with a slight hitch at the end. Here is a solved example of a stoichiometry problem. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html

After you have gone through the example, you will have arrived at the theoretical yield. Just multiply that by 0.400 to arrive at the actual yield.