Reactants: Zn + I 2 Product: ZnI 2

 used to convey as much info. as possible about what happens in a chemical reaction

 Word Equations  write out what chemicals are reacting  hydrogen peroxide → water + oxygen  hydrogen + oxygen → water  Chemical Equations  show the chemical formulas of the chemicals reacting  H 2 O 2 (aq) → H 2 O(l) + O 2 (g)  H 2 (g) + O 2 (g) → H 2 O (l)  (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution (dissolved in water)  the above are often referred to as skeletal equations because they are not mathematically balanced

 chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).  a (+) sign separates molecules on the same side  the arrow is read as “yields”  example C + O 2  CO 2  this reads “carbon plus oxygen react to yield carbon dioxide”

 a catalyst is a substance that speeds up the reaction but is not used up in the reaction  H 2 (g) + O 2 (g) H 2 O (l)  this is written small over the yield arrow MnO 4

 each side of the equation must have the same number of atoms of each element  bicycle example  frame + wheel + handlebar + pedal → bike  frame + 2 wheel + handlebar + 2 pedal → bike  tricycle example  frame + wheels + handlebar + tire → tricycle  frame + 3 wheel + handlebar + 3 tire → tricycle

 when balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction  coefficients represent the number of atoms (or moles) of that compound  sometimes easier if you balance O and H at the end NOT  you may NOT change the subscripts  changing the subscripts changes the compound  ex: H 2 O (water) cannot be changed into H 2 O 2 (hydrogen peroxide) in order to help you balance the equation  H 2 (g) + O 2 (g) → H 2 O (l)

 subscripts tell you how many atoms of a particular element are in a compound.  coefficients tells you about the quantity, or number, of molecules of the compound

 this is NOT balanced

1.A solution of sodium iodide is added to a solution of potassium nitrate yields a potassium iodide precipitate and a sodium nitrate solution. NaI (aq) + KNO 3 (aq)  KI (s) + NaNO 3 (aq) already balanced 2. Magnesium metal burns in oxygen gas with a bright white light to make a white powder called magnesium oxide. Mg (s) + O 2 (g)  MgO (s) + heat 2Mg (s) + O 2 (g)  2MgO (s) + heat 3. Gaseous hydrogen (dihydride) and gaseous oxygen (dioxide) react explosively to form water vapor. H 2 (g) + O 2 (g)  H 2 O (g) + heat 2H 2 (g) + O 2 (g)  2H 2 O (g) + heat

___ Al(s) + ___ Br 2 (l) ---> ___ Al 2 Br 6 (s) 23

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 Al(s) + O 2 (g)  Al 2 O 3 (s)  4Al(s) + 3O 2 (g)  2Al 2 O 3 (s)  NaCl (aq) + AgNO 3 (aq)  AgCl (s) + NaNO 3 (aq)  balanced  Na 2 SiO 3 + HF  H 2 SiF 6 + NaF + H 2 O  Na 2 SiO 3 + 8HF  H 2 SiF 6 + 2NaF + 3H 2 O