chemical reactions

• evidence of a chemical reaction:

  • color changes
  • precipitate forms
  • bubbles form
  • heat is produced/absorbed
• chemical equations: represent chemical reactions where we use symbols instead of words

  • skeletal equation: doesn't indicate relative amounts of the reactants and products
• reactants yield products
• law of conservation of matter: energy cannot be created or destroyed

  • mass must be equal on both sides of reaction in order to be balanced
• synthesis/combination reaction: a chemical change in which two or more substances react to form a new substance

  • exothermic; release energy
  • A + B yields AB
• decomposition reaction: a chemical change in which a single compound breaks down into 2 or more products

  • endothermic; absorbs energy
  • AB yields A + B
• single-replacement reaction: a chemical change in which one element replaces a 2nd element in a compound

  • exothermic; heat is released
• double displacement reaction: a chemical change involving an exchange of positive ions between two compounds

  • often occurs in ionic aqueous solutions
  • often forms a precipitate, gas, or molecular compound