Lec28-Chap-4-3

Lec28-Chap-4-3 - Reactions with Reactant in Limited Supply...

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39 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 2 bread 1 cheese 1 sandwich 2 bread 1 sandwich 40 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
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41 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 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 = Your choice is the limiting reactant. • No = Another reactant is limiting. Reactions with Limited Reactants 42 base all other calculations on the limiting reactant. Bread is limiting 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
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43 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 44 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? Product Method Reactions with Limited Reactants
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45 2 H 2 + O 2 2 H 2 O Moles available: 12.40 3.125 e.g. choose H 2 O 2 needed: 12.40 mol H 2 (1 O 2 /2 H 2 )= 6.20 mol Not available …. O 2 is limiting is limiting . You only need one calculation.
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Lec28-Chap-4-3 - Reactions with Reactant in Limited Supply...

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