Chapter 9: Stoichiometry

Composition Stoichiometry  Deals with the mass relationships of elements in compounds  We did this in Chapter 3  Converting g  mol  molecules and back

Reaction Stoichiometry  Deals with the mass relationships between reactants and products in a chemical reaction  Based on chemical equations and the law of conservation of matter

Reaction Stoichiometry Problems  Problems can be classified according to the information given in the problem, and the information you need to find (the unknown).  We’ll be using tools to convert from the given quantity to the unknown quantity

4 Types of Problems GivenUnknownTools Mol Mole ratio MolMass (g)Mole ratio & molar mass Mass (g)MolMolar mass & mole ratio Mass (g) Molar mass, mole ratio, molar mass

Mole Ratio  We will be using a mole ratio to convert from moles (or grams) of one substance in a reaction to moles (or grams) of another substance  We always need to start with a balanced chemical equation

Mole Ratio  A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction  We get this conversion factor from the balanced chemical equation.  Mole ratios are exact equalities, and thus have infinite number of significant digits (i.e, ignore them when figuring out sig figs)

Mole Ratio 2Al 2 O 3 (l)  4Al(s) + 3O 2 (g)  The coefficients represent the relative amounts in moles of reactants and products.  These relationships can be expressed in mole ratios

6 possible Mole Ratios 2Al 2 O 3 (l)  4Al(s) + 3O 2 (g) 2 mol Al 2 O 3 4 mol Al 4 mol Al2 mol Al 2 O 3 2 mol Al 2 O 3 3 mol O 2 3 mol O 2 2 mol Al 2 O 3 4 mol Al3 mol O 2 3 mol O 2 4 mol Al

Mole Ratios… Your turn List all the possible mole ratios CO 2 (g) + LiOH (s)  Li 2 CO 3 (s) +H 2 O (l) MAKE SURE THE EQUATION IS BALANCED FIRST!!!!!!!!!!!!!!!!!!!!!!!!! 2