Chem121-Chapter-3_Beekman

Chem121-Chapter-3_Beekman - Chapter 3 Stoichiometry:...

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1 Chapter 3 Stoichiometry: Calculations with © R. Spinney 2010 Chemical Equations • Equal quantities of matter exist before and after the chemical reaction (rxn). • At the atomic level: atoms are neither created or destroyed during a chemical rxns! • This is the foundation of chemical equations: descriptions of chemical rxns. reactant(s) product(s) potassium + water potassium hydroxide + hydrogen • Stoichiometry = accounting of chemistry . – Numerical balance sheet of a reaction.
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2 Chemical Equations (cont’d) Arrows: forms or produces (implies 100%) Reactants: appear to the left of the arrow = starting material Products: appear to the right of the arrow = material formed in the rxn Above / below arrow rxn conditions, i.e. heat ( D ), catalysts, solvents etc. Chemical Equations (cont’d) • Physical state indicated by: ( s ) solid K (s) ( l ) liquid H 2 O (l) ( g ) gas H 2 (g) ( aq ) aqueous solution NaOH (aq)
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3 Chemical Equations (cont’d) • Coefficients: indicate number of atoms, molecules or formula units of each reactant and product required. • A balanced rxn eqt: coefficients adjusted so same number of each species on each side of eqt. – Unbalanced rxn eqts are useless when doing calculations! Chemical Equations (cont’d) 2 K( s ) + 2 H 2 O( l ) 2 KOH( aq ) + H 2 ( g ) CH 4 ( g ) + 2 O 2 ( g ) CO 2 ( g ) + 2 H 2 O( l ) • When balancing a reaction: • Change COEFFICIENTS • Cannot change subscripts • WHY NOT?
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4 Chemical Equations (cont’d) 2 x O 2 = 4 O total. Don’t forget to MULTIPLY. Balancing Chemical Equations • Basis: “Law of Conservation of Mass” – mass can neither be created or destroyed! • Dalton – rxns involve rearrangements of atoms! \ # of atoms of reactants = # atoms products
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5 Balancing Chemical Equations (cont’d) • Balancing by inspection: – Consider atoms that appear in only a single substance on each side of the equation. – If several, select the substance with the largest number of atoms of a single element. – Place coefficient to balance on each side of equation. – Balance other atoms – make sure that process does not throw other atoms out of balance. – Balance atoms that appear in two or more places on each side of the equation. – Check to reduce or increase all coefficients to smallest integer ratios. Balancing Chemical Equations (cont’d) Write a balanced chemical equation for reaction of methane gas with oxygen to produce carbon dioxide and water. CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (l) CH 4 (g) + O 2 (g) CO 2 (g) + 2 H 2 O (l) CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l)
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6 Balancing Chemical Equations (cont’d) Write a balanced chemical equation for the following reaction: Solid potassium nitrate decomposes when heated to produce solid potassium nitrite and oxygen gas. KNO
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This note was uploaded on 11/29/2010 for the course CHEM 121 taught by Professor Wyzlouzil during the Summer '07 term at Ohio State.

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Chem121-Chapter-3_Beekman - Chapter 3 Stoichiometry:...

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