Chemistry Chapter 9 Stoichiometry

What is stoichiometry? Stoichiometry = shows relationships between masses of elements in compounds OR between the reactants and products of chemical reaction.

There are different types of reaction- stoichiometry problems. The type is determined by information given in the problem and information you are expected to find.

All Reaction-Stoichiometry Problems Require: Correctly written balanced equation Mole ratio from a balanced equation

Mole Ratio – conversion factor that relates amounts in moles of any two substances involved in a chemical reaction. (remember: coefficients represent moles!) Example: 2 Al 2 O 3 (l)  4 Al( s ) + 3O 2 ( g )

Write all possible mole ratios for this balanced equation: 2HgO ( s )  2Hg ( l ) + O 2 ( g )

Mole-Mole Stoichiometry Calculations Mole-Mole means you are given a known amount of moles of one substance and asked to find the number of relative moles of another substance.

2 Al 2 O 3 (l)  4 Al( s ) + 3O 2 ( g ) This reaction shows that aluminum oxide decomposes into 4 moles of aluminum and 3 moles of oxygen. If the reaction actually yields 25 moles of Al how many moles of oxygen would also be produced? (Mole-Mole Problem) 2.Determine the balanced equation mole ratio that exists between the 2 identified substances 3.Set up problem with mole ratios from balanced equation equal to mole ratios from problem. 4. Solve 1. Make sure this is a correctly written and balanced equation.

2 Al 2 O 3 (l)  4 Al( s ) + 3O 2 ( g ) You have 13.0 mol of aluminum oxide; how many moles of aluminum will this produce?

2 Al 2 O 3 (l)  4 Al( s ) + 3O 2 ( g ) You have 30.4 mol of Al; how many moles of oxygen are produced?

2HgO ( s )  2Hg ( l ) + O 2 ( g ) To yield 20.5 mol of oxygen; how many moles of HgO are required?

Mass-Mass Stoichiometry Calculations These are the most practical calculations because you cannot directly measure moles. However---they rely on moles ratios from the balanced equations. To repeat: YOU MUST HAVE MOLE RATIOS TO SOLVE MASS-MASS CALCULATIONS!!!

1.Is this a correct written and balanced equation? 2.Identify the mole ratio that exists between the 2 substances identified in the problem. 3.Set up the problem with the mole ratio equal to the mass ratio identified in the problem. 4.Substitute molar mass values for the equation mole ratio. 5.Solve. Tin II fluoride, SnF 2, is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride according to the following equation. Sn(s) + 2HF(g)  SnF 2 (s) + H 2 (g) How many grams of SnF 2 are produced from the reaction of g of HF with Sn?

Sodium hydroxide reacts with hydrochloric acid in a double replacement reaction. How many grams of sodium chloride can be produced if you start with 75 grams of sodium hydroxide? 1.Write a correct and balanced equation? 2.Identify the mole ratio that exists between the 2 substances identified in the problem. 3.Set up the problem with the mole ratio equal to the mass ratio identified in the problem. 4.Substitute molar mass values for the equation mole ratio. 5.Solve.