Here are example questions says consider the following balanced chemical reaction. So we have two moles of C6H6 reacting with 15 moles of oxygen gas to produce 12 moles of carbon dioxide gas plus six moles of water as a liquid. It says if a 2.6g sample of C6H6 reacted with excess oxygen to produce 1.25 grams of water, what is the percent yield of water?
All right, they want us to determine the percent yield. We know percent yield equals actual over theoretical times 100. If we read back on the question, they're telling me that I produced 1.25 grams of water. How can I determine if I produced something or made something made product? The only way I would know for sure is if I did the the reaction in real life and obtain that amount. That 1.25g represents our actual yield. So really what we have to do is calculate our theoretical yield.
And remember, our theoretical yield can be determined by using stoichiometry O. If we look here, it says step one, map out the portion of the stoichiometric chart you will use. Well, access, remember means we ignore. They're telling you that I have 2.6g of this reactant. That's the amount they gave to me. So that represents my grams of given. So the map that I'm going to have to workout is grams of given. Convert that into moles of given. Then I'm going to have to convert those moles of given to moles of unknown.
What's our unknown? Well, to figure out the units that I need. Remember, your theoretical yield must have the same units as your actual yield. Our actual yield is in grams per of water, so we have to go all the way to grams of water. So we're going to have here moles of unknown, which is water and then finally end here in grams of unknown. Alright. So that's the stoichiometric chart, at least the portion of it that we need to utilize to get our theoretical yield all right.
So we're going to take the given quantity and change it into moles of given. We have 2.6g of benzene, we have 6 carbons and six hydrogens. When you look on the periodic table and take their atomic masses, add up the six carbons, add up the six hydrogens, you'll have a combined mass of 78.108g per one mole of C6H6. Next we're going to say here, step three, do a mold to mole comparison to convert moles of given into moles of unknown. To do that, remember we look at the coefficients of the balanced equation. We're going to go for moles of C6H6 to moles of water and in our balance equation it is a two to six ratio.
Then it says if necessary, convert the moles of unknown into desired units into the final desired units. Since our actual yield is using grams of water, our theoretical yield needs to go to grams of water, one mole of water. Taking into account the two hydrogens in the one oxygen, it has a combined mass of 18.016g. Then if we multiply everything out into Viva what's on the bottom, we get 1.799 grams of water. This year represents our theoretical yield.
So plug that in to our answer and then step five. We're already doing it. We're plugging in the actual yield and the theoretical yield, and that'll help us define our percent yield. SO12 point 1.25 / 1.799 * * 100 gives me 69.48% as my percent yield for this particular question. So just remember, parts of this are pretty familiar. They're incorporating things we've learned about stoichiometry and limiting reagents, and now just tacking on actual yield. With that information, we're able to find our percent yield for this particular question.
