Percent yield = 70%
Percent yield is the comparison of the amount of product obtained from a reaction with the amount you calculated
General formula:
Percent yield = (Actual yield / theoretical yield )x 100%
An actual yield is the amount of product actually produced by the reaction. A theoretical yield is the amount of product that you calculate from the reaction equation according to the product and reactant coefficients
Reaction
2H₂ (g) + O₂ (g) → 2H₂O (g)
[tex]\tt mass=mol\times MW(mol~ratio~H_2O\div H_2=2\div 2)\\\\mass=(\dfrac{2}{2}\times \dfrac{13.8}{2})\times 18~g/mol\\\\mass=124.2~g[/tex]
[tex]\tt \%yield=\dfrac{87}{124.2}\times 100\%=\boxed{\bold{70\%}}[/tex]
