Calculating Percent Yield
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Calculating percent yield means first finding the theoretical yield from the limiting reactant, then dividing the reaction's actual, measured yield by that theoretical value and multiplying by 100.
Reacting 32.9 g of CCl4 with excess HF is predicted, from the balanced equation and CCl4's identity as the limiting reactant, to give a theoretical yield of about 25.9 g of the product CF2Cl2. If the reaction actually produces 12.5 g of CF2Cl2 once isolated and weighed, dividing 12.5 g by 25.9 g and multiplying by 100 gives a percent yield of about 48.3%, well below the theoretical ceiling.
Dividing the theoretical yield by the actual yield, instead of the reverse, inverts the ratio and can produce a nonsensical result well above 100%.