The balanced equation for the decomposition of sodium bicarbonate is:

2 NaHCO3 --> Na2CO3 + CO2 + H2O

You should be given an amount of sodium bicarbonate to start with, then follow this conversion:

X grams of NaHCO3 x 1/Molecular weight of NaHCO3 x Molar ratio of Na2CO3 to NaHCO3 x Molecular weight of Na2CO3 = Theoretical Yield of Na2CO3

X g NaHCO3 x 1 mole NaHCO3/ x 1 mole Na2CO3/ x 106 g Na2CO3/ = 0.63 *X g Na2CO3 <--Theoretical ---------------------84 g NaHCO3 2 mole NaHCO3 mole Na2CO3

Actual yield is the amount of Na2CO3 is the amount of product you got in your experiment.