120_lecture_4

120_lecture_4 - CHEM 120 Highland Community College Unit 4...

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CHEM 120 Highland Community College Unit 4 John Sullivan Fall, 2007
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Mole Concept Exactly analogous to a dozen. 1 dozen = 12 1 mole = 6.02 C 10 23 The periodic table provides conversion factors between grams and moles via the atomic weight.
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Problem 6.49 How many calcium atoms are in 16.2 g of calcium? ( 29 23 23 mol 6.02 10 16.2 g Ca 2.43 10 atoms 40.1 g mol × = × 
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Problem 6.51 Calculate the molar mass of each of the following compounds: a) Calcium carbonate, CaCO 3 Answer: 40.1+12+ 3(16) = 100.1 g/mol b) Urea, CO(NH 2 ) 2 Answer: 12 + 16 + 2(14+2) = 60 g/mol c) Aluminum sulfate, Al 2 (SO 4 ) 3 Answer: 2(27) + 3(32.1+64) = 342.3 g/mol
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Chemical Equations Statements of chemical change Formulas of reactants are separated from formulas of products by a rightward- pointing arrow. Coefficients are added in front of the formulas to balance the number of atoms on each side of the arrow.
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Problem 6.39 Balance the following equation for the synthesis of hydrazine, N 2 H 4 , a substance used as rocket fuel. NH 3 ( g ) + Cl 2 ( g ) N 2 H 4 ( l ) + NH 4 Cl( s ) Answer: Try a 3 out in front of NH 3 . Unfortunately that would mean 9 H’s on the reactants side. So, try 4. That would be 12 H’s. If we put a 2 in front of the NH 4 Cl, we’d have 12 H’s and the two Cl’s. Write that out and check it. 4NH 3 ( g ) + Cl 2 ( g ) N 2 H 4 ( l ) + 2NH 4 Cl( s )
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Which of the following equations are balanced? Balance those that need it. a) CaC 2 + 2H 2 O Ca(OH) 2 + C 2 H 2 Answer: BALANCED! b) C 2 H 8 N 2 + 2N 2 O 4 2N 2 + 2CO 2 + 4H 2 O Answer: N’s NOT balanced. Change the 2 in front of molecular nitrogen to a 3. c)
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This note was uploaded on 11/06/2010 for the course CHEM 120 taught by Professor Sullivan during the Spring '10 term at Highland CC.

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120_lecture_4 - CHEM 120 Highland Community College Unit 4...

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