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Common Symbols Used in a Chemical Reaction

Common Symbols Used in a Chemical Reaction. (s) = solid (l) = liquid (g) = gas (aq) = solution mixed with water (  ) = presence of heat (catalyst) = compound which speeds up reaction but is not produced or consumed. Types of Reactions.

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Common Symbols Used in a Chemical Reaction

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  1. Common Symbols Used in a Chemical Reaction (s) = solid (l) = liquid (g) = gas (aq) = solution mixed with water () = presence of heat (catalyst) = compound which speeds up reaction but is not produced or consumed

  2. Types of Reactions Synthesis - starts with two elements, not in compounds, and forms only one product. -2 or more elements react to form 1 product. A + B  AB 2Na(s) + Cl2(g) 2NaCl(s)

  3. Types of Reactions Decomposition - always starts with only one reactant. -a single compound breaks down into 2 or more elements or compounds. AB  A + B 2NaN3(s) 2Na(s) + 3N2(g)

  4. Types of Reactions Single-Replacement -always starts with an element and a compound in the reactants. -atoms of one element replace atoms of another element in a compound. AB + C  AC + B Cu(s) + 2AgNO3(aq) 2Ag(s) + Cu(NO3)2(aq)

  5. Types of Reactions Double-Replacement – exchange of ions between two compounds. AB + CD  AD + CB KCN(aq) + HBr(aq) KBr(aq) + HCN(g)

  6. Types of Reactions Combustion – oxygen combines with a substance and release energy in the form of heat and light. 2H2(g) + O2(g) 2H2O(g) C(s) + O2(g) CO2(g)

  7. Formula Mass (Molar Mass) -amount of grams in one mole of that substance. -find molar mass from the Periodic Table

  8. Percent Composition -percent by mass of each element in a compound % Composition = mass of the element x 100 total mass of the compound

  9. Example MgCl2 Step #1 – calculate formula mass for compound Mg – 1 x 24.305 = 24.305 g/mol Cl - 2 x 35.453 = 70.906 g/mol Formula mass = 95.211 g/mol Step #2 – divide each component mass by the formula mass and multiply by 100 Mg: 24.305/95.211 x 100 = 25.528% Cl: 70.906/95.211 x 100 = 74.472% **check that total is 100 when finished**

  10. Empirical Formula -symbols for the elements contained in a compound with subscripts showing the smallest whole number mole ratio possible. -may or may not be the same as the actual molecular formula.

  11. Empirical Formula Example Problem: 36.5% Na, 25.4% S, 38.1% O; Determine the empirical formula. A. convert grams to moles Na - 36.5 g Na x 1 mol Na = 1.58 mol Na 23.0 g Na S - 25.4 g S x 1 mol S = 0.791 mol S 32.1 g S O - 38.1 g O x 1 mol O = 2.38 mol O 16.0 g O

  12. Empirical Formula B. Divide all by smallest molar amount (in example, 0.791 mol) Na: 1.58 mol / 0.791 mol = 2 Na S: 0.791 mol / 0.791 mol = 1 S O: 2.38 mol / 0.791 mol = 3 O C. This whole number represents the smallest mole ratio possible for that substance. Na2SO3

  13. Molecular Formula -the actual number of atoms of each element in one molecule or formula unit of the substance. Molecular Formula=(Empirical Formula)n n= integer; factor by which the subscripts of the empirical formula must be multiplied to obtain molecular formula.

  14. Molecular Formula Example: Molar Mass of Acetylene: 26.04 g/mol Mass of empirical formula CH: 13.02 g/mol experimentally determined molar mass of acetylene mass of empirical formula CH 26.04 g/mol = 2.00 13.02 g/mol Molecular Formula of Acetylene= (CH)2 = C2H2

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