UNIT 7: CHEMICAL REACTIONS

EVIDENCE OF CHEMICAL CHANGE  Changes in Energy  Release of energy as heat  Release of energy as light  Production of sound  Reduction or increase in temperature  Absorption or release of electrical energy  Formation of new substances  Formation of a gas  Formation of a precipitate (an insoluble solid)  Change in color  Change in odor A NEW SUBSTANCE MUST BE FORMED!

WRITING CHEMICAL EQUATIONS  Shows chemical formulas and relative amounts of all reactants and products – like a recipe  Start with a word equation  Reactant produces/yields/forms product  R + R  P + P  Separate the chemical names with plus signs  Next, write the formulas for each chemical – this does not show amounts  The equation must be balanced to complete the recipe

 The arrow separates the reactants from products  The s, l, g, aq are written after the formulas to indicate state

BALANCING EQUATIONS  The Law of Conservation of Mass must be observed!! Matter, mass, atoms, electrons, etc. are not created or destroyed only REARRANGED!  Once the formulas are established for the chemicals, they cannot be changed (this changes the substance) – DO NOT Change subscripts!  COEFFICIENTS are used to balance the elements in the equation

BALANCING CHEMICAL EQUATIONS  Identify reactants and products  Count atoms  Insert Coefficients  Verify Results  Hydrogen and oxygen react to form water  H 2(g) + O 2(g)  H 2 O (g)  H: 2 2  O: 2 1  2H 2(g) + O 2(g)  2H 2 O (g)  H: 4 4  O: 2 2  BALANCED! 2 x 2 = 4

HELPFUL HINTS  Polyatomic ions can be balanced as a unit, provided it stays in tact on both sides  Balance polyatomic ions and metals first  Balance hydrogen, oxygen, and water last!  If you run into a problem, for instance a whole number coefficient will not work, try doubling ALL coefficients  Don’t worry if your numbers are too big, just reduce all numbers by the same factor if possible

THERE ARE 5 TYPES OF REACTIONSREACTIONS 1. Synthesis 2. Decomposition 3. Single Displacement (or Replacement)  Have to use the Activity Series of Metal 4. Double Displacement (or Replacement)  Have to use the solubility rules 5. Combustion

SYNTHESIS (COMBINATION) – “BUILDING”, COMES FROM GREEK WORD THAT MEANS “TO PUT TOGETHER” A + B  AB 2Na + Cl 2  2NaCl Formation of binary compound MO + H2O  base K 2 O + H 2 O  2KOH Metal oxide- water reaction (NM)O + H2O  acid SO3 + H2O  H 2 SO 4 Nonmetal oxide-water reactions

DECOMPOSITION – OPPOSITE OF SYNTHESIS, ROTTING, BREAKING APART AB  A + B 2H 2 O  2H 2 + O 2 Binary Compounds MCO3  MO + CO2 CuCO 3  CuO + CO 2 Metallic Carbonates MHCO3  MO + H20(l) + CO 2(g) NaHCO 3  NaO + H 2 0 (l) + CO 2(g) Metallic hydrogen carbonates

DECOMPOSITION CONTINUED MOH  MO + H2O Ca(OH) 2  Ca + H 2 O Metallic hydroxides MClO3  MCl + O2 2KClO 3  KCl + 3O 2 Metallic chlorates Acid  (NM)O + H2O H2SO4  SO 3 + H 2 O Oxyacids decompose to nonmetal oxides and water

SINGLE REPLACEMENT – AN ELEMENT REPLACES ANOTHER IN A COMPOUND A + BC  AC + B Li + NaCl  LiCl + Na Metal-metal replacement M + H2O  MOH + H2 Ca + 2H 2 O  Ca(OH) 2 + H 2 Active metal replaces H from water M + HX  MX + H2 Zn + 2HCl  ZnCl 2 + H 2 Active metal replaces H from acid D + BC  BD + C F 2 + 2KCl  2KF + Cl 2 Halide-halide replacement Activity Series

DOUBLE REPLACEMENT: 2 ELEMENTS SWITCH PLACES COMBUSTION: BURNING IN OXYGEN AB + CD  AD + CB NaCl + AgNO 3  NaNO 3 + AgCl (s) Formation of a precipitate from solution Acid + base  salt + water HCl + NaOH  NaCl + H 2 O Acid-base neutralization reaction CxHy + O 2  CO2 + H20 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 0 Hydrocarbon + oxygen  carbon dioxide and water Solubility rules

USING THE REFERENCE TABLES  Just because an equation can be written does NOT mean that the reaction will actually happen!  If it is single replacement – Refer to the activity series  The reacting metal must be more active (higher up) than the metal that is to be replaced, otherwise NO RXN occurs  If it is double replacement – refer to solubility rules  The rxn only occurs if water, a gas, or a precipitate is formed  Precipitate – an insoluble compound, determine by using solubility rules

SOLUBILITY RULES  1 All compounds containing alkali metal cations and the ammonium ion are soluble.  2 All compounds containing NO 3 -, ClO 4 -, ClO 3 -, and C 2 H 3 O 2 - anions are soluble.  3 All chlorides, bromides, and iodides are soluble except those containing Ag +, Pb 2+, or Hg  4 All sulfates are soluble except those containing Hg 2 2+, Pb 2+, Sr 2+, Ca 2+, or Ba 2+.  5 All hydroxides are insoluble except compounds of the alkali metals, Ca 2+, Sr 2+, and Ba 2+.  6 All compounds containing PO 4 3-, S 2-, CO 3 2-, and SO 3 2- ions are insoluble except those that also contain alkali metals or NH 4 +.