Good Afternoon! 9/13/2014

Good Afternoon! 9/13/2014 • Today we will… • Hand out the Schedules • Finish the problems from yesterday • Hand out books • Discuss tow other areas of Stoichiometry • Limiting Reactants (it is just like it sounds) • Percent yield, theoretical yield

Equation 2 4 5 2 P + O2 P2O5 First you have to balance it, so you can have the ratios. Given: 3 moles of P Find: _____ moles of P2O5 Start with what moles of what you are given. Multiply by the Mole Ratio Finally an answer pops out 3 moles P = 1.5 moles P2O5

Equation 2 Part II 4 5 2 P + O2 P2O5 How many Moles of Phosphorus do you need to produce 2.5 moles of P2O5? Given: 2.5 moles of P2O5 Find ____ moles P Start with what moles of what you are given. Multiply by the Mole Ratio Finally an answer pops out 2.5 moles P2O5 = 5 moles P

Equation 2 Part II Step 2 How many grams of Phosphorus would that be? Given: 5 moles of P Find ______ grams P Start with what moles of what you are given. Multiply by the Molar mass Finally an answer pops out 5 moles P = 154.85 grams P

One more practice, only this one will be a big one. • Use the following reaction to answer the question below. • Li3N + H2O  NH3 + LiOH • Use the steps, balance, convert to moles, use the ratio, then go to what you are asked. • If you have 32.9 grams of Li3N how many grams of water do you need?

Here is the answer.Li3N + 3 H2O  NH3 + 3 LiOH

Practice Problem 2 2 3 2 Al + Cl2 AlCl3 First you have to balance it, so you can have the ratios. Given: 5.67 grams of Al Find: _____ liters of Cl2

2 3 2 Al + Cl2 AlCl3

Limiting Reactant The limiting reactantis the reactant that is consumed first,and then limits the amount of product formed. What is the limiting reactant in the reaction below?

Limiting Reagents - Combustion

If you have the following amounts for the following reaction, which one is the limiting Reactant? • 2 H2 + O2 2 H2O 6.4 moles H2 3.4 moles O2

So what you have to do is just pick one, doesn’t matter which just pick. Find out how many moles are needed to consume that one and then compare. Since we have more O2 than we need H2 is limiting reactant

Percent Yield! • So here’s the thing, if you take the reaction that we looked at before, only this time we’ll see how much NH3 we can make. • Li3N + 3 H2O  NH3 + 3 LiOH • If I send you to the lab with 32.9 g Li3N, do you think you’ll get 16.09 g NH3?

Here are a few Vocabulary words you’ll need. • Theoretical Yield: this is the amount that you are supposed to get (assuming not one atom is lost) You have to calculate this using the process. • Actual Yield: This is the amount that you get when you do the reaction in the lab. • Percent Yield: This is what % the Actual Yield is of the Theoretical yield.

Theoretical yieldLet’s say you do the following reaction in the presence of excess (more than enough) Iron and 15.0 grams of Sb2S3Sb2S3 + 3 Fe  2 Sb + 3 FeS

Actual Yield • Let’s say you do the experiment and end up with 9.84 grams of Sb, what is your percent yield?

Percent Yield 10.75 g Sb is our theoretical yield & 9.84 g Sb is our Actual yield, so…

Good Afternoon! 9/13/2014