Describing

Chemical

Reactions

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 gas2. 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

Balancing Chemical Equations 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

How about these? ?KCl + ? H2SO4 ? HCl + ? K2SO4

2KCl + H2SO4 2HCl + K2SO4

NaCl (aq) + AgNO3 (aq) AgCl (s) + NaNO3 (aq) balanced

Al(s) + O2(g) Al2O3(s) 4Al(s) + 3O2(g) 2Al2O3(s)