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 × = × 
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.
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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