Chapter 12 - Stoichiometry I ‘m back! I ‘m back!

Proportional Relationships 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. I have 5 eggs. How many cookies can I make? 5 eggs 5 doz. 2 eggs = 12.5 dozen cookies Ratio of eggs to cookies

Stoichiometry is the study of the relationships between reactants and products in a chemical reaction. is based on the mole ratio Mole Ratio Mole Ratio indicated by coefficients in a balanced equation 2 Mg + O 2  2 MgO 2 Mg + O 2  2 MgO

Interpreting Balanced Equations 2H 2 + O 2  2H 2 O  2 molecules of hydrogen and 1 molecule of oxygen form 2 molecules of water.  2 moles of hydrogen and 1 mole of oxygen form 2 moles of water.  2 dozen molecules hydrogen and 1 dozen molecules of oxygen form 2 dozen molecules of water.

Coefficients The coefficients show the ratios of each substance in the equation. This also applies to mass relationships. We can check this using moles. 2 moles H g H 2 1 mole H 2 =4.04 g H 2 1 mole O g O 2 1 mole O 2 = g O g H 2 + O g H 2 + O 2 2H 2 + O 2  2H 2 O 2 moles H 2 O Reactants: Product: g H 2 O 1 mole H 2 O = g H 2 O

Types of Calculations 1. mole to mole The mole ratio is the ratio between any two substances in a reaction and will be used in all calculations Ex. 2 Al 2 O 3  Al + 3O 2 Each time 2 moles of Al 2 O 3 are decomposed, 4 moles of Al and 3 moles of O 2 and produced. 2 moles Al 2 O 3 3 mole O 2 2 moles Al 2 O 3 or These are possible conversion factors.

Ex. 1 How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decompose? 2 Al 2 O 3  4Al + 3O mol Al 2 O 3 3 mol O 2 2 mol Al 2 O 3 = 5.01 mol O 2 *Practice problem 1: C 2 H 2 + O 2  CO 2 + H 2 O (unbalanced) If 3.84 moles of C 2 H 2 are burned, how many moles of O 2 are needed?

2. moles to grams given moles  mole ratio  molar mass given moles  mole ratio  molar mass types of problems (continued) Ex. 2 If 1.50 moles of Fe are used, how many grams of copper II sulfate would form? 2Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu 1.50 mol of Fe 3 mol CuSO 4 2 mol Fe1 mol CuSO g g CuSO 4 = 359 g = 359 g CuSO 4

*Practice problem 2: C 2 H 2 + O 2  CO 2 + H 2 O (unbalanced) If moles of O 2 are used, how many grams of C 2 H 2 are burned? 3. grams to moles given mass  molar mass  mole ratio Ex. 3 If 146 g of NaCl are produced in the following reaction, how many moles of Cl 2 were consumed? 2Na + Cl 2  2NaCl 146 g NaCl 1 mol NaCl 1 mol Cl 2 = 1.25 mol g NaCl g NaCl 2 mol NaCl

types of problems (continued) 4. grams to grams given mass  molar mass  mole ratio  molar mass Ex. 4 Ex. 4 If 10.8 g of Fe are added to a solution of CuSO 4, how many grams of solid copper would form? 2Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu 10.8 g Fe 1 mol Fe 3 mol Cu g Cu = 18.4g g Fe 2 mol Fe 1 mol Cu *Practice problem 3: *Practice problem 3: Calculate the no. of moles of CH 4 used to produce 1.8 g of H 2 O. CH 4 + 2O 2  CO 2 + 2H 2 O

*Practice problem 4: *Practice problem 4: Zinc reacts with iodine to form zinc iodide (ZnI 2 ). Write the balanced equation for this reaction. Calculate the grams of ZnI 2 that would be produced from a g sample of Zn.