Limiting Reactants, Excess Reactants and Theoretical Yield

Limiting Reactant A limiting reactant in a chemical reaction is the substance that: Is used up first. Stops the reaction. Limits the amount of product that can form.

Reacting Amounts In a table setting, there is 1plate, 1 fork, 1 knife, and 1 spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item? Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Reacting Amounts Four table settings can be made. Initially Used Left over plates 5 forks 6 spoons 4 knives 7 The limiting item is _______________.

Example of Everyday Limiting Reactant How many peanut butter sandwiches could be made from 8 slices bread and 1 jar of peanut butter? With 8 slices of bread, only 4 sandwiches could be made. The bread is the limiting item.

Example of Everyday Limiting Reactant How many peanut butter sandwiches could be made from 8 slices bread and 1 tablespoon of peanut butter? With 1 tablespoon of peanut butter, only 1 sandwich could be made. The peanut butter is the limiting item.

Limiting Reactants When 4.00 mol H2 is mixed with 2.00 mol Cl2,how many moles of HCl can form? H2(g) + Cl2(g)  2HCl (g) 4.00 mol 2.00 mol ??? mol Calculate the moles of product from each reactant, H2 and Cl2. (Use mole ratio) The limiting reactant is the one that produces the smaller amount of product.

Limiting Reactants Using Moles HCl from H2 HCl from Cl2

Limiting Reactants Using Moles If 4.80 mol Ca mixed with 2.00 mol N2, which is the limiting reactant? 3Ca(s) + N2(g)  Ca3N2(s) Moles of Ca3H2 from Ca Moles of Ca3H2 from N2

Limiting Reactants Using Mass Calculate the mass of water produced when 8.00 g H2 and 24.0 g O2 react? 2H2(g) + O2(g) 2H2O(l) Step #1: Calculate the number of moles of product formed from both masses of reactants to determine the limiting reactant.

Limiting Reactants Using Mass Step #2: Determine the limiting reactant. Step #3: Convert lowest # of moles of product to grams of product.

Limiting Reactants Using Mass What is the maximum number of grams of copper(I) sulfide produced when 80.0-g of copper reacts with 25.0-g of sulfur? 2Cu(s) + S(s)  Cu2S(s)

Calculating Leftover Reactant How much of the excess reactant is leftover after the reaction has been completed?

Percent Yield Actual Yield = experimental chemical rxn Theoretical Yield = based on calculations

Example of Percent Yield A piece of copper with a mass of 5.00-g is placed in a solution of silver nitrate containing excess AgNO3. The silver metal produced has a mass of 15.2-g. What is the percent yield for this reaction? Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

One More Example… Determine the percent yield when a solution containing 2.80-g of Al(NO3)3 is mixed with a solution containing excess NaOH if 0.966-g of Al(OH)3 precipitate is recovered.