Chem121-Chapter-3-SH

Chem121-Chapter-3-SH - Chapter 3 Stoichiometry:...

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Chapter 3 Stoichiometry: Calculations with © R. Spinney 2009 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) Æ product(s) potassium + water Æ potassium hydroxide + hydrogen • Stoichiometry = accounting for chemistry. Chemical Equations (cont’d) • Arrows: Æ 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 ( Δ ), catalysts, solvents etc.
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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) 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 ) Æ 2 KOH( aq ) + H 2 ( g ) CH 4 ( g ) + 2 O 2 ( g ) Æ CO 2 ( g ) + 2 H 2 O( l )
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Chemical Equations (cont’d) 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 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.
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Balancing Chemical Equations (cont’d) Write a balanced chemical equation for reaction of methane gas with oxygen to produce carbon dioxide and water. 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. Balancing Chemical Equations (cont’d) Problem: balance the following eqt PCl 3 + H 2 O Æ H 3 PO 3 + HCl
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Balancing Chemical Equations (cont’d) Problem: Write a balance eqt for: calcium oxide reacts with phosphoric acid to produce calcium phosphate and water. Balancing Chemical Equations
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Chem121-Chapter-3-SH - Chapter 3 Stoichiometry:...

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