1. Unit 5: The Mole and Stoichiometry

2. What Can A Coefficient Equal? A coefficient represents the number of elements or molecules in a chemical equation. It is different from a subscript which measures the number of atoms or polyatomic ions within a molecule. 2 CO + O 2  2 CO 2 C oefficients S ubscripts Come in front of an element or molecule Big numbers Means that every element or molecule in a compound get multiplied by it. Come after an element or polyatomic ion Small numbers Only tell how many of an element there are within a compound

3. A Coefficient can represent two different things: 1. Number of molecules of a reactant or product in an equation. 2. Number of moles of a reactant or product in an equation. In either case, the coefficients give the ratio between the numbers in a chemical reaction (this is why balancing is important)! 2CO(g) + 1O 2 (g)  2CO 2 The reactant ratio is 2:1

4. Using the Mole Coefficients in balanced chemical equations represent MOLES or Molecules Zn + 2 HCl  ZnCl 2 + H 2 1 mole (or atom) of Zn reacts with 2 moles (or molecules) of hydrochloric acid to produce 1 mole(or molecule) of zinc chloride and 1 mole(or molecule) of hydrogen gas.

5. Back to the reaction Zn + 2 HCl  ZnCl 2 + H 2 To carry out this reaction, how much zinc and HCl will be needed to make the reaction go to completion? 1 mole of Zn and 2 moles of HCl How many moles of HCl will be needed if I have 2 moles of zinc? 4 moles of HCl

6. How many moles of Copper (I) Sulfide could be produced from 6 moles of Copper (I) Chloride reacting with an excess of H 2 S gas? 1. Write a balanced equation. Determine what you start with and what you want to know. H 2 S + CuCl  Cu 2 S + HCl 22

7. 2. Covert moles of what you start with to moles of what you want to know using a mole ratio. *A mole ratio compares two products or reactants using the coefficients of the balanced equation (in this case 2 moles CuCl:1 mole Cu 2 S). 6 moles CuCl H 2 S + 2CuCl  Cu 2 S + 2HCl 1 mole Cu 2 S 2 moles CuCl = 3 moles Cu 2 S

8. H 2 S + 2CuCl  Cu 2 S + 2HCl How many moles of HCl would be produced starting with the same amount? 6 moles CuCl2 moles HCl 2 moles CuCl = 6 moles HCl

9. Al + H 2 CO 3  Al 2 (CO 3 ) 3 + H 2 Suppose Carlos gets 10 moles of Aluminum for his birthday. How much of each product can he make? 23 3 10 moles Al1 mole Al 2 (CO 3 ) 3 2 moles Al = 5 moles Al 2 (CO 3 ) 3 10 moles Al3 moles H 2 2 moles Al = 15 moles H 2