Presentation on theme: "Starter A sandwich consists of two slices of bread, 3 slices of meat, and one slice of cheese. For each of the following amounts, determine the number."— Presentation transcript:
1 StarterA sandwich consists of two slices of bread, 3 slices of meat, and one slice of cheese.For each of the following amounts, determine the number of sandwiches that can be made and what is left over:6 bread, 10 meat, 4 cheese slices10 bread, 6 meat, 8 cheese slices25 bread, 40 meat, 12 cheese slices
4 Why is there a limiting reactant? a reaction rarely has exactly the right amount of each reactantusually have some left overlimiting reactantreactant that limits the amount of product createdalways completely used upexcess reactantreactant not completely used up
5 When do you have to find a LR? whenever two amounts of reactants are given in a problemwhen only one amount of reactant is given in a problem, then the other is assumed to be in excess
6 Finding Limiting Reactant using reactants Figure out how much you need of B if you use up all of AConvert grams A to grams B using stoichiometryYou may start with either reactantDetermine whether you will have enoughIf you don’t have enough of B, then B is LRIf you don’t have enough of A, then A is LR
7 Finding Limiting Reactant using products Convert each of the reactant amounts into an amount of product (doesn’t matter which product)Compare product amounts and find lowest amount.Whichever reactant led to lowest product amount is LR
8 Example 1The reaction begins with 2.51 g of HF and 4.56 g of SiO2. What is the limiting reactant and the excess reactant? How much excess reactant will be left over?Write the balanced chemical equationSiO2(s) + 4HF(g) SiF4(g) + 2H2O(l)
9 Example 1Find the number of moles available of each reactant:
10 Example 1If we use up all of the HF, how much SiO2 will we need to go with it?Do we have enough SiO2?mol available > mol neededYES- there will be some left overLimiting Reactant : HF
11 How much of the product can be formed? Start conversion with amount of limiting reactant.Convert to amount of product using stoichiometry
12 Example 1 How many grams of water could be formed? Convert grams of HF to moles.Convert moles of HF to moles of water.Convert moles to grams using molar mass.
13 Example 2 A reaction was done with 36.8 g C6H6 and 41.0 g of O2. Write the balanced chemical equation2C6H6 + 15O2 12CO2 + 6H2OWhat is the limiting reactant and how much of each product can be produced?
14 Example 2 Reactant Method = 113 g O2 Product Method = 25.5 g H2O 36.8 g C6H6 1 mol C6H6 15 mol O2 32 g O278.12 g C6H6 2 mol C6H6 1 mol O2= 113 g O2Because 113 g O2 is greater than what we have available, O2 is LRProduct Method36.8 g C6H6 1 mol C6H6 6 mol H2O g H2O78.12 g C6H6 2 mol C6H6 1 mol H2O= 25.5 g H2O41.0 g O2 1 mol O2 6 mol H2O g H2O32 g O mol O2 1 mol H2O= 9.24 g H2OBecause 9.24 is less than 25.5, O2 is the LR
15 Example 2Once you find the LR, you can then calculate the amount of each product formed…Amount of H2O41.0 g O2 1 mol O2 6 mol H2O g H2O32 g O mol O2 1 mol H2O= 9.24 g H2OAmount of CO241.0 g O2 1 mol O mol CO g CO232 g O mol O2 1 mol CO2= g CO2
16 Example 3If the reaction below begins with grams of Fe and 37.5 grams of oxygen, what is the limiting reactant?4Fe(s) + 3O2(g) 2Fe2O3
17 Example 3How many grams of oxygen will be left over after the reaction?How many grams of iron (III) oxide can be formed?