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Chemical Reactions

Chemical Reactions. Writing and Balancing Chemical Reactions. Parts of a reaction equation :. Reactants → Products (s) = solid (l) = liquid (g) = gas ( aq ) = aqueous (dissolved in water) ( ppt ) = precipitate (solid formed from 2 liquids) ↓ = ppt forms → = “yields” ↑ = gas formed

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Chemical Reactions

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  1. Chemical Reactions Writing and Balancing Chemical Reactions

  2. Parts of a reaction equation: • Reactants → Products • (s) = solid • (l) = liquid • (g) = gas • (aq) = aqueous (dissolved in water) • (ppt) = precipitate (solid formed from 2 liquids) • ↓ = ppt forms • → = “yields” • ↑ = gas formed • ↔ = reversible reaction • ∆ = heat • ___° C = temp. of reaction

  3. Ways to write chemical equations: 1. Complete Chemical Equations • ALWAYS: balanced, chemical formulas, reactants, products • SOMETIMES: states of matter, catalyst included • Ex. 2 H2O2 (aq)  2 H20(I) + O2 (g)

  4. 2. Formula Equation (Skeleton Equation) • ALWAYS: shows formulas, unbalanced, no states of matter • Ex. H2O2  H20+ O2

  5. 3. Word Equation • ALWAYS: words (no formulas), reactants, products, unbalanced, no states of matter • Ex. Hydrogen peroxide  water + oxygen

  6. 4. Sentence Equation: • ALWAYS: written in complete sentences, states of matter when possible, not balanced • Ex. An aqueous solution of hydrogen peroxide forms liquid water and oxygen gas.

  7. Balancing Chemical Equations: • Why? Law of Conservation of Mass • Steps: • Atom inventory – count how many of each • Polyatomic ions – count as one as long as it exists on both sides • Do elements that appear only once per side first • Do oxygen LAST • Add/ change only coefficients (numbers in front) NOT SUBSCRIPTS • Get lowest ratio

  8. Balancing Example Al + HCl AlCl3 + H2 2 Al + 6 HCl 2 AlCl3 + 3 H2 * must have same number of each atom type on each side

  9. Reaction Types • Synthesis: A + B  AB • Decomposition: AB  A + B • Single Replacement (SRR): A + BC  AC + B • Double Replacement (DRR): AB + CD  AD + CB • Combustion: X + O2 CO2 + H2O

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