Lecture 10 - Lecture 10: Lecture 10: Limiting Reactants;...

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1 Lecture 10: Limiting Reactants; Combustion Analysis 2 Reactions with Reactant in Limited Supply Given 10 slices of cheese and 14 slices of bread. How many sandwiches can you make? Balanced equation 1 cheese + 2 bread 1 sandwich 1 cheese Ł 2 bread 1 cheese Ł 1 sandwich 2 bread Ł 1 sandwich 1-2
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3 Two methods can be used. Both treat as a unit conversion problem Product Method Product Method Calculate the product from each starting material. ± The reactant giving the smallest smallest number is limiting. 10 cheese x = 10 sandwiches 1 sandwich 1 cheese 14 bread x = 7 sandwiches 1 sandwich 2 bread Correct answer Bread is limiting. It will be used up first Reactions with Limited Reactants 4 Reactant Method Reactant Method Pick a reactant; calculate the amount of the other(s) needed. Enough? e.g. choose bread cheese needed: 14 bread (1 cheese /2 bread ) = 7 Available …. bread is limiting . e.g. choose cheese bread needed: 10 cheese (2 bread/1 cheese) = 20 Not available …. bread is limiting bread is limiting . •Yes = You r cho ice is the l im i t ing reac tan t . •No = Ano r t l i t . Reactions with Limited Reactants 2-1
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5 base all other calculations on the limiting reactant. Bread is limiting Sandwiches made Sandwiches made 14 bread (1 sandwich / 2 bread ) = 7 sandwiches Cheese remaining Cheese remaining 14 bread (1 cheese / 2 bread ) = 7 cheese used. Started with 10 cheese. Cheese remaining 10 – 7 = 3 slices Reactions with Limited Reactants 6 How much water will be produced by the combustion of 25.0 g of H 2 in the presence of 100. g of O 2 ? Write a balanced equation: n H2 = 25.0 g = 12.40 mol H 2 1 mol H 2 2.016 g 2 H 2 (g) + O 2 (g) 2 H 2 O( l ) n O2 = 100. g = 3.125 mol O 2 1 mol O 2 32.00 g Reactions with Limited Reactants The limiting reactant is the one you do not have enough of. 3-3 3-4 Step one.
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7 2 H 2 + O 2 2 H 2 O Moles available: 12.40 3.125 Using H 2 12.40 mol H 2 (2H 2 O /2H 2 ) = 12.40 mol H 2 O Using O 2 3.125 mol O 2 (2 H 2 O/1 O 2 ) = 6.250 mol H 2 O O 2 gave less water. O 2 is limiting is limiting . Base all calculations on O 2 6.250 mol H 2 O x (18.02 g/ 1 mol ) = 113. g water 113. g water How much water will be produced?
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Lecture 10 - Lecture 10: Lecture 10: Limiting Reactants;...

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