Then you calculate the theoretical yield of product from the amount of the limiting reactant.
EXAMPLE
Aspirin is prepared by the reaction between acetic anhydride and salicylic acid.
#"acetic anhydride + salicylic acid → aspirin + acetic acid"#
#"C"_4"H"_6"O"_3 + "C"_7"H"_7"O"_3 → "C"_9"H"_8"O"_4 + "C"_2"H"_4"O"_2#
#color(white)(mm)"A"color(white)(ml) +color(white)(m) "B"color(white)(mm) →color(white)(mll) "C"color(white)(mll) +color(white)(ml) "D"#
What is the theoretical yield of aspirin (#"C"#) if you reacted 4.32 g of acetic anhydride (#"A"#) with 2.00 g of salicylic acid (#"B"#)?
Solution
The molar masses are
Acetic anhydride = #"A" = "C"_4"H"_6"O"_3 = "102.1 g/mol"#
Salicylic acid = #"B" = "C"_7"H"_6"O"_3 = "138.1 g/mol"#
Aspirin = #"C" = "C"_9"H"_8"O"_4 = "180.2 g/mol"#
Identify the limiting reactant
We calculate the moles of each reactant and then use the molar ratios from the balanced equation to calculate the moles of aspirin.
#"Moles of aspirin from A" = 4.32 cancel("g A") × (1 cancel("mol A"))/(102.1 cancel("g A")) × "1 mol C"/(1cancel("mol A")) = "0.0423 mol C"#
#"Moles of aspirin from B" = 2.00 cancel("g B") × (1 cancel("mol B"))/(138.1 cancel("g B")) × "1 mol C"/(1 cancel("mol B")) = "0.0145 mol C"#
#"B"# gives the smaller amount of aspirin, so #"B"# is the limiting reactant.
Calculate the theoretical yield
#0.0145 cancel("mol C") × "180.2 g C"/(1 cancel("mol C")) = "2.61 g C"#
