If 50.0 g of Ba(CN)2 reacts to produce 12.9 g of HCN, what is the percent yield?

Answer 1

Here is a worked example of a stoichiometry problem. This will give you the theoretical yield of HCN. Then
%yield = (actual yield/theor yield)*100 = ?
http://www.jiskha.com/science/chemistry/stoichiometry.html