LESSON 2: Chemical Reactions

• Chemical reaction is…

  • Process of breaking chemical bonds in one or more substances

  Reforming new bonds to create new substances
•  Evidence of Chemical Change

  1. Formation of gas – bubbling
  2. Formation of precipitate – turns cloudy and new solid is formed
  3. Release of energy (heat or light)
  4. Color change
  5. Temperature change – energy is released or absorbed
• Chemical reactions start with reactants (starting substances) combined to make products (new substances resulted from chemical reaction. 
• LAW OF CONSERVATION OF MASS


  Antoine Laurent Lavoisier (1789)  –

  “Mass is neither created nor destroyed in chemical reactions.”

  • It is applied by balancing the number and type of atoms on either side of the equation using coefficients but never changing the subscripts.
• In conservation of mass…

  • A closed system must be used
  • When in a closed container, you can show that the mass before and after the reaction is the same