In this example, we will solve a limiting reagent problem using dimensional analysis. Our problem reads: "In the reaction below, 178 grams of C8H18 and 525 grams of oxygen react to completion. What mass of CO2 gas can be produced, and what mass remains of the excess reactant? If 432 grams of CO2 gas is produced when the experiment is performed, what is the percent yield?" First, we'll use dimensional analysis to determine the mass of CO2 gas produced. We are given amounts of two different reactants, so we know this is a limiting reagent problem. We'll have to use each reactant to determine how much carbon dioxide gas can be produced. To determine how much carbon dioxide gas can be produced from C8H18, we begin with our 178 grams of C8H18 and use dimensional analysis to convert to grams of carbon dioxide. Our first step is to use the molar mass of C8H18 to convert from grams to moles. Then, we can use stoichiometry or the coefficients in the balanced chemical equation to convert from moles of C8H18 into moles of carbon dioxide gas. Finally, we can use the molar mass of carbon dioxide gas to convert from moles of carbon dioxide to grams of carbon dioxide. If you put this in your calculator, you should get 549 grams of carbon dioxide. Since we're given amounts of both C8H18 and oxygen gas, we have to determine how much CO2 can be produced from the oxygen gas. We can use a similar dimensional analysis. We have 525 grams of oxygen gas. We use its molar mass to go from grams of oxygen to moles of oxygen. Using stoichiometry and the coefficients in the balanced chemical equation, we can convert from moles of oxygen gas into moles of carbon dioxide. Then, using the molar mass of carbon dioxide, we go from moles of carbon dioxide to grams of carbon dioxide. If you put this in your calculator, you should get 462 grams of carbon dioxide. Whichever reactant produces less carbon dioxide is our limiting reagent. It's the one that's going to run out first. So, we run out of oxygen gas first before we run out of C8H18. Therefore, the total amount of carbon dioxide that can be produced is 462 grams. In Part B, we want to know how much of the excess reactant remains. For this calculation, our first step is to determine how much octane (C8H18) is needed to completely react with our limiting reagent, oxygen gas. We'll start our dimensional analysis with our grams of oxygen and convert to moles of oxygen using the molar mass. Then, we can convert from moles of oxygen to moles of C8H18 using stoichiometry and the coefficients in the balanced chemical equation. Finally, we can convert from moles of C8H18 into grams of C8H18. This dimensional analysis will give us how many grams of C8H18 are needed to completely react with our limiting reagent, oxygen. In step two, we'll subtract how much of the excess reactant we used from how much we began with. We began with 178 grams of C8H18 and we used 150 grams in our reaction with oxygen. So, we have 28 grams of remaining C8H18 at the end of the reaction after it has gone to completion. For Part C, we are given how much carbon dioxide gas is actually produced when the experiment is performed, and we want to calculate the percent yield. Our equation for percent yield is: Percent yield = (actual yield / theoretical yield) * 100% Our actual yield is given in the problem, which is 432 grams of carbon dioxide gas that is produced when the experiment is actually performed. Our theoretical yield, calculated in Part A, is 462 grams of carbon dioxide. When we divide these numbers and multiply by 100%, we get 93.5% yield.