 A chemical reaction is the process of breaking of chemical bonds (ionic or covalent) in one or more substances, and the reforming of new bonds to create new substances  indicators of chemical change are: 1. formation of new gas 2. formation of new precipitate (solid) 3. release of energy (heat or light) 4. color change

 energy is stored in the ionic and covalent bonds of molecules  exothermic reaction– energy is released (burning)  endothermic reaction– energy is absorbed (cold packs)

 some important chemical reactions  burning of fossil fuels  photosynthesis  rusting of metals

 Conservation of mass  matter cannot be created nor destroyed in chemical reactions

 chemical equations convey as much info. as possible about what happens in a chemical reaction during a chemical change

 each side of the equation must have the same number of atoms of each elements  bicycle example  skeletal equation  frame + wheel + handlebar + pedal → bike  balanced equation  frame + 2 wheels + handlebar + 2 pedals → bike  tricycle example  skeletal equation  frame + wheels + handlebar + bell → tricycle  balanced equation  frame + 3 wheels + handlebar + bell → tricycle

NOT BALANCED!

 this is NOT balanced

 ?KCl + ? H 2 SO 4  ? HCl + ? K 2 SO 4  2KCl + H 2 SO 4  2HCl + K 2 SO 4  NaCl (aq) + AgNO 3 (aq)  AgCl (s) + NaNO 3 (aq)  balanced  Al(s) + O 2 (g)  Al 2 O 3 (s)  4Al(s) + 3O 2 (g)  2Al 2 O 3 (s)