1. Stoichiometry: Limiting and Excess Reagents

2. Bon Appetite Suppose you are a chef preparing French toast for a group of people. You make French toast the way you have always made it: one egg for every three slices of bread. You never waiver from this recipe, because the French toast will be either too soggy or too dry. There are 8 eggs and 30 slices of bread in the pantry. How many slices of French Toast can you make?

3. Limiting and Excess Reagents So far we have only looked at chemical reactions in which the quantities of reagents were in Stoichiometric Amounts – The reactants are balanced such that there will be no reactants left over. In practice, stoichiometric amounts are rarely used, and instead one reactant is generally added in excess.

4. Limiting and Excess Reagents Example: Calcium carbonate can be used to scrub sulfur dioxide from emissions. The chemical reaction occurring is: SO 2 (g) + CaCO 3 (s)  CaSO 3 (s) + CO 2 (g) SO 2 and CaCO 3 will react with each other in a 1:1 ratio. Why is it wise to have an excess of calcium carbonate?

5. Limiting and Excess Reagents By having an excess of CaCO 3, all the the SO 2 will be consumed preventing it from entering the atmosphere. SO 2 (g) + CaCO 3 (s)  CaSO 3 (s) + CO 2 (g) In this reaction, SO 2 is the limiting reagent, while CaCO 3 is the excess reagent.

6. Limiting and Excess Reagents Limiting Reagent: The reactant that is completely consumed in a chemical reactant – this amount also determined the quantity of product that will be formed Excess Reagent: The reactant that is still present after the reaction is complete

7. Example Sodium reacts with chlorine to produce sodium chloride: 2 Na + Cl 2  2 NaCl What is our mole ratio? If I have 6 mol of Na, how many mol of Cl 2 are required? What if I had 5 moles of Cl 2 ? – Limiting Reagent? – Excess Reagent?

8. Example 2 mol Mg and 5 mol O 2 are placed in a reaction vessel. The Mg is ignited: Mg + O 2  MgO Balance this equation and identify the limiting reagent in this experiment. How much of the excess reagent is left unreacted? What mass of product is formed?

9. Example Determine the amount of titanium metal produced when 2.8 mol of titanium(IV) chloride reacts with 5.4 mol of magnesium. 1.Balanced chemical equation, include given and required values 2.Determine the limiting reagent 3.Use the amount of products based on limiting reagent

10. Example Methanol, CH 3 OH, can be made using a synthesis reaction involving carbon monoxide and hydrogen. What mass of methanol can be produced from 9.80 g of carbon monoxide and 1.30 g of hydrogen? Suppose that a solution containing 3.50 g of Na 3 PO 4 is mixed with a solution containing 6.40 g of Ba(NO 3 ) 2. How many g of Ba 3 (PO 4 ) 2 can be formed?

11. Homework Read section 7.3 Questions p. 332 #1-4 p. 334 #1-3