Lec-27-Chap4-2

# Lec-27-Chap4-2 - Using Chemical Equations How much of...

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18 Using Chemical Equations • How much of reactant B do I need to use with reactant A? •In moles (balancing equations) •In grams or volumes (also using molar mass, or PV=nRT) • How much product C will I get from a reaction of X moles A and Y moles B? (balancing equations) •In grams or volumes (also using molar mass, or PV=nRT) • If I add X grams A and Y grams B, how much C will I produce? (balancing, limiting reagents) •In grams or volumes (using molar masses, or PV=nRT) •Will any of A or B be left over? (limiting reagents) • What if I don’t get as much product as I thought I should get? •Calculating % yield 19 Think of a chemical equation as an assembly line Balancing Chemical Equations ++ + + 4 2 1 1 1 In what ratios do we need parts? How many tires, doors etc. are needed for each car? How many cars can we make if we have 11 tires, 3 steering wheels, 9 doors, 5 windshields?

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21 1. Write an unbalanced equation with correct formulas for all substances. 2. Balance the atoms of one element. a. Start with the most complex molecule, and elements that appear in only 1 molecule on each side of the arrow b. Change the coefficients in front of the molecules c. Do NOT alter the chemical formulas 3. Balance the remaining elements, leaving molecules with only 1 element for last. 4. Check the atoms are all balanced. Balancing Chemical Equations 22 step 2 A l + Fe 2 O 3 A l 2 O 3 + Fe 1 A l (2Fe + 3O) (2A l + 3O) 2Fe step 4 – balanced 2 Balance : A l + Fe 2 O 3 A l 2 O 3 + Fe not balanced not balanced balanced balanced not balanced step 3 A l + Fe 2 O 3 A l 2 O 3 + 2 Fe 2A l (2Fe + 3O) (2A l + 3O) 2Fe 2 step 1 A l + Fe 2 O 3 A l 2 O 3 + Fe 1 A l (2Fe + 3O) (2A l + 3O) 1Fe Balancing Chemical Equations
24 Balancing Chemical Equations Balance C and H in C 2 H 4 O 2 first (save O for last): C 2 H 4 O 2 + O 2 2 2 H 2 O + 2 2 CO 2 Combustion of hydrocarbon: C

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Lec-27-Chap4-2 - Using Chemical Equations How much of...

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