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  • Hot air balloons use large propane torches to heat the air in the balloon. Unfortunately, that much flame can cause a catastrophic fire (see bottom image). Fortunately, the 11 people in this balloon survived. All hydrocarbons (like propane) produce carbon dioxide and water as the combustion products. The unbalanced combustion reaction for propane is: C 3 H 8 + O 2 --> CO 2 + H 2 O
  • DECOMPOSITION PICTURE Here's a fun decomposition reaction. The starting compound is ammonium dichromate. When heated, it begins to decompose into nitrogen gas, water vapor and powdered chromium (III) oxide. It looks like a volcano with ash being spread all over the place. This looks like the compound is burning, but looking at the chemical equation we see no oxygen is being consumed. So the flame it produces does not need oxygen. So you can't put out this kind of "fire" by smothering it like most fires. http://www.chemistryland.com/CHM130W/08-Equations/TypesReactions/TypesReactions.htm
  • Here is a chemistry example that was shown in an earlier tutorial. This is also a double-replacement reaction. Here the barium atom swaps places with the calcium atom. When that happens, we make barium sulfate which is given to patients to drink, so x-rays can see the stomach and intestines. As a kid I had to drink it, and it tasted like chalk. It was bad. They could have at least sweetened it. (roll cursor over image to see the double-replacement animation) http://www.chemistryland.com/CHM130W/08-Equations/balancing/BalancingChemEq.htm
  • Decomposition Single Rep Synthesis Double rep
  • Cl 2 + 2KBr  KCl + Br 2 2Ag 2 O  4Ag + O 2 2Na + Cl 2  2NaCl PbCl 2 + Li 2 SO4  PbSO 4 + 2LiCl C 6 H 12 O 6 +6 O 2 -> 6C O 2 + 6H 2 O 1. Single 2. Decomposition 3. Synthesis 4. Double 5 Combustion

Types reactions2012 Types reactions2012 Presentation Transcript

  • CH 10 CHEMICAL REACTIONS
  • What’s the center or target? Building Blocks Putting them together Rearranging them Disassembling them
  • Chemical Reactions
  • Evidence of Chemical Reaction 1. Color change 2. Energy change: absorbed or released
  • 3. Odor changes or production 4. Gas production 5. Precipitate formation
    • Chemical equations are used to write/ represent chemical reactions
      • Show Reactants : the starting substances
      • Show Products : resulting or ending substances
      • Use yield ( ->) sign instead of equal sign (=)
    Reactants Products
    • Word equation : uses words
      • Setup: Reactant 1 + Reactant 2  Product 1
      • Ex: Iron(s) + Chlorine(g)  Iron(III) Chloride(s)
    • Skeleton equation: uses formulas
      • Ex: Fe(s) + Cl 2 (g)  Fe Cl 3 (s)
      • Chemical equation : balanced equation
      • Shows matter is conserved during a reaction (Law of Conservation of Mass)
      • Ex: 2 Fe(s) + 3 Cl 2 (g)  2 Fe Cl 3 (s)
      • Bolded NUMBER in FRONT are called Coefficients
    • Write the skeleton equation
    • Count the atoms of each element in the reactants
    • Count the atoms of each element in the products
    • Change the coefficients to make both sides of the equation the equal (=) (DO NOT CHANGE SUBSCRIPTS)
    • Write the coefficient(s) in the lowest ratio possible
    • Check your work
      • Ex: H 2 (g) + O 2 (g)  H 2 O(g)
      • Balanced: 2 H 2 + O 2 (g)  2 H 2 O(g)
    • Practice website www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html
    Steps to Balance a Chemical Equation
  • Examples
    • Hydrogen gas and bromine gas form gaseous hydrogen bromide
      • H 2 + Br 2  HBr
      • Balanced: H 2 + Br 2  2 HBr
    • Balancing hints:
      • When odd numbers of oxygen needed use a fraction, then multiply by two
        • Al + O 2  Al 2 O 3
        • 2 Al + O 2  Al 2 O 3 need three oxygens (odd number)
        • 2 Al + 1.5 O 2  Al 2 O 3 fractions/ decimals cannot be left as coefficients
        • 4 Al + 3 O 2  2 Al 2 O 3 Whole equation multiplied by two to get rid of decimals or fractions
      • Try the following:
        • C 2 H 6 + O 2  CO 2 + H 2 O
  • Examples/ hints cont.
    • When balancing with polyatomic ions found both in the reactants and products, replace the ions by a variable.
      • Fe 2 O 3 + H 2 SO 4  Fe 2 (SO 4 ) 3 + H 2 O
      • Fe 2 O 3 + H 2 X  Fe 2 ( X ) 3 + H 2 O
      • Fe 2 O 3 + 3 H 2 X  Fe 2 ( X ) 3 + 3 H 2 O
      • Fe 2 O 3 + 3 H 2 SO 4  Fe 2 (SO 4 ) 3 + 3 H 2 O
    • Balancing with elements that appear more than twice in different formulas ( leave for last! )
      • CO 2 + H 2  C H 4 + H 2 O hydrogen appears more than twice
      • CO 2 + H 2  CH 4 + 2 H 2 O balance C and O
      • CO 2 + 4 H 2  CH 4 + 2 H 2 O
      • Synthesis – formation, combining
      • Combustion - burns in air, reaction with O 2
      • Decomposition – breaking down into components
      • Single-Replacement – exchange of 1 element in a compound
      • Double-Replacement – exchange of ions b/w 2 compounds
    AB -> A + B AB + CD -> AD + BC
    • Synthesis Reaction
      • Chemical reaction in which two or more substances combine to form one single product.
      • A + B  AB
        • Ex: 2Na(s) + Cl 2 (g)  2NaCl(s)
        • 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s)
    • Combustion Reaction
      • Oxygen combined with a substance releasing energy in the form of light and heat
      • Many combustion reactions are also synthesis reactions
      • A + O 2  AO
        • Ex: 2H 2 (g) + O 2  2H 2 O(g)
    • Decomposition reactions
      • Only one compound
      • Breaks down into 2 or more compounds or elements
      • Setup: AB  A + B
      • Often requires an energy source (i.e. heat, light, electricity)
        • Ex: NH 4 NO 3 (s)  N 2 O(g) + 2H 2 O(g)
        • The above reaction occurs when the reactant is heated
    • Replacement Reactions
      • involve the replacement of an element in compound
      • 2 kinds of replacement reactions:
        • Single
        • Double
    • Single Replacement reactions
      • When atoms of one element replace the atoms of another element in a compound
      • Setup:
      • Whether or not a metal will replace another metal or any other substance depends on the reactivity it has
    A+ BX  AX + B
    • Double Replacement reactions
      • Invovles the exchange of ions between 2 compounds
      • Setup: AX + BY  AY + BX
      • If a solid is produced during the reaction it is called a precipitate
  • Practice – Classify the following reactions
  • Practice – Classify the following equations & Balance them
    • Cl 2 + KBr  KCl + Br 2
    • Ag 2 O  Ag + O 2
    • Na + Cl 2  NaCl
    • PbCl 2 + Li 2 SO4  PbSO 4 + LiCl
    • C 6 H 12 O 6 + O 2 -> C O 2 + H 2 O