Summary
Highlights
The video introduces the concepts of theoretical and percent yield using the example of propane reacting with air to produce carbon dioxide. The first step in solving such a problem is to write a balanced chemical reaction.
For combustion reactions, the speaker recommends balancing carbon atoms first, then hydrogen atoms, and finally oxygen atoms. This strategy is effective because oxygen exists as a pure element (O2), allowing its coefficient to be adjusted without affecting other elements. The example reaction C3H8 + O2 → H2O + CO2 is balanced to C3H8 + 5O2 → 4H2O + 3CO2.
The percent yield formula is introduced: (Actual Yield / Theoretical Yield) * 100%. The actual yield is the amount of product obtained from an experiment (given as 70 grams of CO2 in this problem), while the theoretical yield is the maximum possible amount if the reaction were 100% efficient.
To calculate the theoretical yield, the grams of the limiting reactant (propane, 30 grams) must be converted to grams of the product (CO2). Air provides an excess of O2, making propane the limiting reactant. The calculation involves converting grams of propane to moles using its molar mass (44.094 g/mol), then using the molar ratio from the balanced equation (1 mole C3H8 to 3 moles CO2), and finally converting moles of CO2 to grams using its molar mass (44.01 g/mol).
Following the stoichiometric steps, the theoretical yield of CO2 from 30 grams of propane is calculated to be 89.83 grams. This represents the maximum amount of CO2 that could be produced under ideal conditions.
With the actual yield (70 grams) and theoretical yield (89.83 grams) for CO2, the percent yield is calculated: (70 / 89.83) * 100%, resulting in a percent yield of 77.9%.