Reactants: Zn + I 2 Product: Zn I 2 SAVE PAPER AND INK!!! When you print out the notes on PowerPoint, print "Handouts" instead of "Slides" in the print setup. Also, turn off the backgrounds (Tools>Options>Print>UNcheck "Background Printing")!

Their Job: Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al (s) + 3 O 2 (g) ---> 2 Al 2 O 3 (s)

 Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken  What do we call those “outermost parts”???  Valence electrons  Symbols represent elements,  formulas describe compounds,  chemical equations describe a chemical reaction

reactants products…  Chemical equations show the conversion of reactants into products…  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”

 The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide.  The chemical equation for this reaction, C + O 2  CO 2, contains the same information as the English sentence but has quantitative meaning as well.

Because of the law of conservation of matter, conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

 States that mass is neither created nor destroyed in any ordinary chemical reaction.  Or more simply, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants).  Ex’s  1.00g carbon g sulphur ? 6.34g carbon disulphide  2.00g carbon g sulphur ? 12.68g carbon disulphide

 Solid ___  Liquid (l)  Gas ___  Aqueous solution (aq)  Catalyst H 2 SO 4  Escaping gas (  )  Change of temperature (  )

not  When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the …  subscripts.  Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)

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

4 Al(s) + 3 O 2 (g)  2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules ---produces---> 4 Al atoms + 3 O 2 molecules ---produces---> 2 molecules of Al 2 O 3 2 molecules of Al 2 O 3

There are four basic steps to balancing a chemical equation. 1. Write out the equation (done for you on homework) Na 3 PO 4 + Fe 2 O 3  Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O 3  Na 2 O + FePO 4

2. Find the number of atoms for each element on each side.  YOU MUST COMBINE ALL of the same element together…  ex  Na- 3Na-2  P-1P-1  Fe- 2Fe- 1  O- 7O-5  HINT- write them in the same order on both sides so that it is easier to compare them Na 3 PO 4 + Fe 2 O 3  Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O 3  Na 2 O + FePO 4

3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.  Lets do one from your HW …

___ H 2 + ___ O 2 ---> ___ H 2 O 22 What Happened to the Other Oxygen Atom????? This equation is not balanced!

4. Check your answer to see if:  The numbers of atoms on both sides of the equation are now balanced.  The coefficients are in the lowest possible whole number ratios. (reduced)

Some Helpful Hints for balancing equations:  Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last.  IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (Because O is diatomic as an element)

___ Al + ___ Br 2  ___Al 2 Br 6 23

____C 3 H 8 (g) + _____ O 2 (g) ----> _____CO 2 (g) + _____ H 2 O(g) ____B 4 H 10 (g) + _____ O 2 (g) ----> ___ B 2 O 3 (g) + _____ H 2 O(g)

Sodium phosphate + iron (III) oxide  sodium oxide + iron (III) phosphate Na 3 PO 4 + Fe 2 O > Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O > Na 2 O + FePO 4