HONORS CHEMISTRY

Feb 27, 2012

Brain Teaser

Cu + 2 AgNO3 2 Ag + Cu(NO3)2

– How many moles of silver are produced when 25 grams of silver nitrate reacts with excess amount of copper?

– How many grams of silver nitrate are needed to produce 50 grams of silver?

Agenda• Brain Teaser• Notes: Limiting Reactants• Work on Mixed Stoichiometry Practice Worksheet 2• Homework– Complete Worksheet

Limiting Reactants

Limiting Reactants

• Reactant that is completely used up in a chemical reaction

• Determines the maximum amount of product that can be formed.

Limiting Reactants

• Why is this important?– The quantities of products formed in a reaction

are always determined by the quantity of the limiting reactant.

Limiting Reactants• Analogy: making cheese sandwiches

Limiting Reactants

Limiting Reactants

Limiting ReactantsLimiting Reactants

2H2 + O2 2H2O

What is the limiting reactant?

Limiting ReactantsLimiting Reactants

2H2 + O2 2H2O

What is the limiting reactant?

Limiting Reactants• How many grams of water can I make from 22

grams of hydrogen and 195 grams of oxygen?– Write a balanced chemical equation

H2 + O2 H2O

– What is the limiting reactant?• Answer: Do two stoichiometry calculations

– Determine mass of product produced by each reactant

– How do you know?

Determining the limiting reactants• The limiting reagent may not be obvious!!

Practice Problem• If 11.3 grams of sodium chloride are formed in the

reaction described above, what is the percent yield of this reaction?

Can you really get out everything that goes in?

% yield = experimental yield x 100theoretical yield

Experimental or actual yield determined in the lab

Theoretical or expected yield determined by stoichiometry

Practice Problem• If 35 grams of C6H10 reacts with 45 grams of

oxygen, how many grams of carbon dioxide will be formed?– What is the limiting reactant?– How much of the excess reactant is left over after

the reaction ?– If 35 grams of carbon dioxide are actually formed

from the reaction, what is the percent yield of this reaction?

Partner Quiz

1) CaCl2 + Na2CO3 CaCO3 + 2NaCl

5.45 g 4.55 g ? How much CaCO3 (in g) is formed? What is the percent yield for this reaction if 3.96 g of calcium carbonate was isolated from the reaction?