2/20 Notes – Limiting Reactants

 

  1. Limiting Reactant

            A.        Def

                        1.         Limiting Reactant – reactant that stops a reaction; reactant that is completely used up in the reaction

                        2.         Excess Reactant – reactant that is leftover in a reaction

            B.        S’mores

                        1 Graham Cracker + 1 Marshmallow + 3 squares of chocolate à 1 S’more

                        23 / box                       36 / bag                       6 bars with 24 squares each

                        23 S’more                    36 S’more                    24 S’mores

                        We will run out of chocolate first meaning that chocolate is the limiting reactant, we will only be able to make 24 S’mores

                        Graham Crackers and marshmallows are the excess reactants

            C.        Methods for solving

                        1.         Product check

n      Which reactant will make the least product if you have 5 grams of hydrogen and 25 grams of oxygen reacting to make water?

Write a balanced chemical equation                           2 H2 + O2 à 2 H2O

Determine amount of product using each reactant     5 g H2  1 mol H2          2 mol H2O       18 g H2O         45 g of H2O made by 5 g H2

                                                                                                2 g H2              2 mol H2          1 mol H2O

                                                                                    25 g O2            1 mol O2          2 mol H2O       18 g H2O         28 g of H2O made by 25 g O2

                                                                                                            32 g O2            1 mol O2          1 mol H2O

                                                                                    Oxygen will make the least product

 

            2.         Reactant Comparison

n      Which reactant is the limiting reactant and how much of the excess reactant remains if 35 g of sodium react with 123 g of chlorine reacts to form sodium chloride?                                                                                                                                                         Have

Write a balanced chemical equation                           2 Na + Cl2 à 2 NaCl

Determine limiting reactant by doing a stoich line from reactant to reactant

                                                                                    35 g Na           1 mol Na         1 mol Cl2         71 g Cl2           54 g Cl2 Needed

                                                                                                            23 g Na           2 mol Na         1 mol Cl2

                                                                                    Na is the limiting reactant

                                                                                    Cl2 is the excess reactant

Subtract (Have – Need) to find how much excess will be leftover 123 g (given in problem) – 54 g (found on stoich line) = 69 g excess