Limiting & Excess

Cookie Stoichiometry To make one batch, it requires: 2 eggs 2 cups of flour 2/3 cups of butter How many batches could you make with… 4 eggs 6 cups of flour 2/3 cups of butter The cups of butter was your limiting reagent The eggs and flour were your excess reagents But how could you show this mathematically…?

2 Together…. 3 on your Own! Whiteboard!

Example 1 20.00 g of H2 react with 100.0 g of O2 according to the reaction 2 H2 + O2  2 H2O Which reactant is limiting and which reactant is in excess?

Example 1 1. Calculate the number of moles of a product formed. Mole of H2O (based on H2) = 20.00 g H2 x 1 mol H2 2 mol H2O 10.0 mole H2O 2.0 g H2 2 mol H2 Mole of H2O (based on O2) = 100.0 g O2 x 1 mol O2 2 mol H2O 6.25 mol H2O 32.0 g O2

Example 1 Determine the limiting and excess reactants. O2 is the limiting reactant. H2 is the excess reactant. 2. How much H2 (in grams) is left after O2 runs out?

Example 1 3. To find mass of H2 in excess, find the mass of H2 which will react based on the mass of the limiting reactant. Mass of H2 (based on O2) = 100.0 g O2 x 1 mol O2 2 mol H2 2.0 g H2 12.5 g H2 32.0 g O2 1 mol H2

Example 1 4. Then, subtract the mass of H2 which reacts from the starting mass of H2. Mass of H2 (in excess) = mass H2 (at start) – mass H2 (reacted) = 20.00 g – 12.5g = 7.5 g Take Attendance

FeCl2 + KNO3 + HCl  FeCl3 + NO + H2O + KCl Example 2 If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction FeCl2 + KNO3 + HCl  FeCl3 + NO + H2O + KCl What is the limiting reactant? How many grams of each “excess” reactant left in the reaction vessel?

3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl Example 2 If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl What is the limiting reactant? How many grams of each “excess” reactant left in the reaction vessel?

3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl Example 2 If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl What is the limiting reactant? KNO3 How many grams of each “excess” reactant left in the reaction vessel?

3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl Example 2 If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl What is the limiting reactant? KNO3 b) How many grams of each “excess” reactant are actually present in excess? FeCl2 = 0.8g, HCl = 18.5g

Example 3 If 3.2 g of CuSO4, 2.5 g of water and 3.0 g of SO2 are reacted together in the reaction: CuSO4 + H2O + SO2  Cu + H2SO4 Which reactant is the limiting reactant? What is the mass of each of the excess reactants?

Example 4 700. mL of 0.350 M ammonia (NH3) solution is mixed with 15.0 g of solid magnesium to produce magnesium nitride and hydrogen gas. Which reactant is in excess? How much (in grams) of the excess reactant remains after the reaction is complete?

Example 5: For the reaction: TiO2(aq) + B4C(g) + C(s)  TiB2(aq) + CO(g) If 11.5 L of 0.800 M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.

Example 5: For the reaction: 2TiO2(aq) + B4C(g) + 3 C(s)  2TiB2(aq) + 4CO(g) If 11.5 L of 0.800 M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.