Hi Karla, percent yield = (actual yield/ theoretical yield ) x 100
actual yield is the amount of product obtained (this is experimental result), and
theoretical yield is the amount of product calculated based on the balanced chemical equation (this is theoretical or predicted amount).
Thus, 14.61 g H2 is the actual yield.
To find the theoretical yield, you have to calculated the amount of H2 that will be produced from 58.96 g of methane according to the equation.
CH4(g) + 2H2O(g)-> 4 H 2 (g) + CO2(g)
mol: 1 mol 4 mol
gram: 16 g 8 g (use the molar mass to convert mol. to gram)
8 g H2 is formed from 16 g of CH4. Thus, from 58.96 g CH4
(8 g H2/16 g CH4) x 58.96 g CH4 = 29.48 g H2 will be formed
percent yield = (14.61 g/29.48) x 100 = 49.5 %