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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.

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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 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 of sandwiches that can be made and what is left over: 6 bread, 10 meat, 4 cheese slices 6 bread, 10 meat, 4 cheese slices 10 bread, 6 meat, 8 cheese slices 10 bread, 6 meat, 8 cheese slices 25 bread, 40 meat, 12 cheese slices 25 bread, 40 meat, 12 cheese slices

2 Starter 6 bread, 10 meat, 4 cheese slices 6 bread, 10 meat, 4 cheese slices 3 sandwiches 3 sandwiches 0 bread, 1 meat, 1 cheese 0 bread, 1 meat, 1 cheese 10 bread, 6 meat, 8 cheese slices 10 bread, 6 meat, 8 cheese slices 2 sandwiches 2 sandwiches 6 bread, 0 meat, 6 cheese 6 bread, 0 meat, 6 cheese 25 bread, 40 meat, 12 cheese slices 25 bread, 40 meat, 12 cheese slices 12 sandwiches 12 sandwiches 1 bread, 4 meat, 0 cheese 1 bread, 4 meat, 0 cheese

3 Ch. 9 Stoichiometry 9.3 Limiting Reactant

4 Why is there a limiting reactant? a reaction rarely has exactly the right amount of each reactant a reaction rarely has exactly the right amount of each reactant usually have some left over usually have some left over limiting reactant limiting reactant reactant that limits the amount of product created reactant that limits the amount of product created always completely used up always completely used up excess reactant excess reactant reactant not completely used up reactant not completely used up

5 When do you have to find a LR? whenever two amounts of reactants are given in a problem whenever two amounts of reactants are given in a problem when only one amount of reactant is given in a problem, then the other is assumed to be in excess when 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 1. Figure out how much you need of B if you use up all of A  Convert grams A to grams B using stoichiometry  You may start with either reactant 2. Determine whether you will have enough  If you don’t have enough of B, then B is LR  If 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) Convert each of the reactant amounts into an amount of product (doesn’t matter which product) Compare product amounts and find lowest amount. Compare product amounts and find lowest amount. Whichever reactant led to lowest product amount is LR Whichever reactant led to lowest product amount is LR

8 Example 1 The reaction begins with 2.51 g of HF and 4.56 g of SiO 2. What is the limiting reactant and the excess reactant? How much excess reactant will be left over? The reaction begins with 2.51 g of HF and 4.56 g of SiO 2. What is the limiting reactant and the excess reactant? How much excess reactant will be left over? Write the balanced chemical equation Write the balanced chemical equation SiO 2 (s) + 4HF(g)  SiF 4 (g) + 2H 2 O(l)

9 Example 1 Find the number of moles available of each reactant: Find the number of moles available of each reactant:

10 Example 1 If we use up all of the HF, how much SiO 2 will we need to go with it? If we use up all of the HF, how much SiO 2 will we need to go with it? Do we have enough SiO 2 ? Do we have enough SiO 2 ? mol available > mol needed mol available > mol needed YES- there will be some left over YES- there will be some left over Limiting Reactant : HF Limiting Reactant : HF

11 How much of the product can be formed? 1. Start conversion with amount of limiting reactant. 2. Convert to amount of product using stoichiometry

12 Example 1 How many grams of water could be formed? How many grams of water could be formed? Convert grams of HF to moles. Convert grams of HF to moles. Convert moles of HF to moles of water. Convert moles of HF to moles of water. Convert moles to grams using molar mass. Convert moles to grams using molar mass.

13 Example 2 A reaction was done with 36.8 g C 6 H 6 and 41.0 g of O 2. A reaction was done with 36.8 g C 6 H 6 and 41.0 g of O 2. Write the balanced chemical equation Write the balanced chemical equation 2C 6 H O 2  12CO 2 + 6H 2 O What is the limiting reactant and how much of each product can be produced? What is the limiting reactant and how much of each product can be produced?

14 Example 2 Reactant Method 36.8 g C6H61 mol C6H615 mol O232 g O g C6H62 mol C6H61 mol O2 = 113 g O2 Because 113 g O2 is greater than what we have available, O2 is LR Product Method 36.8 g C6H61 mol C6H66 mol H2O18.02 g H2O g C6H62 mol C6H61 mol H2O = 25.5 g H2O 41.0 g O21 mol O2 6 mol H2O g H2O 32 g O2 15 mol O2 1 mol H2O = 9.24 g H2O Because 9.24 is less than 25.5, O2 is the LR

15 Example 2 Once you find the LR, you can then calculate the amount of each product formed… Once you find the LR, you can then calculate the amount of each product formed… Amount of H2O 41.0 g O21 mol O2 6 mol H2O g H2O 32 g O2 15 mol O2 1 mol H2O = 9.24 g H2O 41.0 g O21 mol O2 12 mol CO g CO2 32 g O2 15 mol O2 1 mol CO2 = g CO2 Amount of CO2

16 Example 3 If the reaction below begins with grams of Fe and 37.5 grams of oxygen, what is the limiting reactant? If the reaction below begins with grams of Fe and 37.5 grams of oxygen, what is the limiting reactant? 4Fe(s) + 3O 2 (g)  2Fe 2 O 3

17 Example 3 How many grams of oxygen will be left over after the reaction? How many grams of oxygen will be left over after the reaction? How many grams of iron (III) oxide can be formed? How many grams of iron (III) oxide can be formed?


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