Warmup 11/5/15 Finish the story: "I wanted to make cookies, so I bought 12 eggs and 50 lbs of flour. As I started to make them..." Objective Tonight’s Homework To define the concept of the "limiting reactant“ and “excess” Finish in class practice

Notes on Limiting Reactants Let’s look at our warmup. Likely, most of you ended your story with something like having too much flour. We can relate this to chemistry.

Notes on Limiting Reactants Let’s do an example: Cu + 2 AgNO 3  Cu(NO 3 ) Ag Above, we have copper and silver nitrate combining to form silver and copper nitrate.

Notes on Limiting Reactants Let’s do an example: 10 mol Cu + 2 AgNO 3  Cu(NO 3 ) Ag Above, we have copper and silver nitrate combining to form silver and copper nitrate. Let’s add a number of moles here.

Notes on Limiting Reactants Let’s do an example: 10 mol Cu + 2 AgNO 3  Cu(NO 3 ) Ag Above, we have copper and silver nitrate combining to form silver and copper nitrate. Let’s add a number of moles here. With this setup what can we say about the number of moles of each after the reaction?

Notes on Limiting Reactants Let’s do an example: 10 mol Cu + 2 AgNO 3  Cu(NO 3 ) Ag Above, we have copper and silver nitrate combining to form silver and copper nitrate. Let’s add a number of moles here. With this setup what can we say about the number of moles of each after the reaction? Well, we use two AgNO 3 molecules for every Cu atom, so AgNO 3 runs out with 5 moles of Cu left

Notes on Limiting Reactants Visually, we can imagine our reaction going in steps of something like this: (1 dot = 1 mole) Cu + 2 AgNO 3  Cu(NO 3 ) Ag

Notes on Limiting Reactants We say that the starting AgNO 3 was a limiting reactant. (Reactants are what you have before chemicals react. Products are what you have after. Reactants on left, products on right.)

Notes on Limiting Reactants We say that the starting AgNO 3 was a limiting reactant. (Reactants are what you have before chemicals react. Products are what you have after. Reactants on left, products on right.) A limiting reactant is anything going into a chemical equation that runs out while we still have other stuff that could react. It limits how much chemical reaction we get. When doing problems involving something running out, we just have to keep in mind that we have to stop when we run out of our limiting reactant.

Notes on Limiting Reactants We can also have an excess reactant. This is a reactant where we can assume we have infinite amounts. That we’ll never run out. So if I’m combining an excess of chemical “A” with some amount of chemical “B”, B will always be my limiting reactant.

Practice on Limiting Reactants Let’s practice as a class. For each problem, balance the reaction, name its type, and calculate the number of moles formed for each product assuming we have 10 moles of all reactants. 1) H 2 SO 4 + NaOH  Na 2 SO 4 + H 2 O 2) N 2 + H 2  NH 3 3) Al + Cl 2  AlCl 3 4) H 2 O 2  H 2 O + O 2 5) Na + O 2  Na 2 O 6) CH 4 + O 2  CO 2 + H 2 O 7) NaOH + H 3 PO 4  Na 3 PO 4 + H 2 O

Exit Question Which job or situation below would use knowledge from today's stuff? a) A chemical cleaner production plant b) A factory that creates brass (a combination of tin and copper) c) A factory that mass produces frozen pizzas d) A cook working in the kitchen of a large restaurant e) All of the above f) None of the above