Silicon dioxide reacts with carbon to form silicon carbide and carbon monoxide as shown in the unbalanced reaction below. Determine the percent yield of silicon carbide if 79.1 grams of carbon reacts with an excess of silicon dioxide and 67.4 g of silicon carbide is actually recovered. SiO2 + C → SiC + CO

Excess silicon dioxide" tells us carbon is the limiting reactant, and thus the amount of silicon carbide produced depends on how much carbon is available to react.
*Based on the balanced equation, for every 3 moles carbon reacted, 1 mole silicon carbide is produced.
*Molar mass carbon: 12.01 g/mol
*Molar mass silicon carbide: 28.09 g + 12.01 g = 40.1 g/mol

79.1 g carbon x (1 mol carbon / 12.01 g carbon) x (1 mol silicon carbide / 3 mol carbon) x (40.1 g silicon carbide / 1 mol silicon carbide) = 88.04 g silicon carbide