Balancing Chemical Equations

Demonstration!!!!!!!! Sentence - Combine dissolved Lead (II) Nitrate with aqueous Potassium Iodide to yield aqueous Potassium Nitrate and solid Lead (II) Iodide Word – Lead (II) Nitrate + Potassium Iodide  Potassium Nitrate + Lead (II) Iodide Chemical- Pb(NO 3 ) 2(aq) +2KI (aq)  2KNO 3(aq) + PbI 2(s) This is called a double displacement reaction  more on this to come.

Balanced Chemical Equations Atoms can’t be created or destroyed in a reaction: – All the atoms we start with we must end up with(meaning: balanced!) A balanced equation has the same number of each element on both sides the equation.

Chemical Reactions While the reactions show what is used up and what is produced, they do not reflect the proper number of each type of atom required for the reaction. H 2 + O 2  H 2 O How many oxygen atoms are on the right? 1 How many oxygen atoms are on the left? 2 Does this make sense? What happened to that other oxygen atom. We use coefficients to “balance the equation” ensure that there are the same number of each type of atom on either side of the equation. Afterwards check to make sure the number of atoms on the left = the right **Using coefficients doesn’t change the reaction, it simple shows us how many atoms were actually involved** 22

Rules for balancing: 1)Assemble the correct formulas for all the reactants and products, using “+” and “→” 2)Count the number of atoms of each type appearing on both sides 3)Balance the elements one at a time by adding coefficients (the numbers in front) where you need more – save balancing the H and O until Last (hint: I prefer to save O until the very last) 4)Double Check to make sure it is balanced by counting the atoms on both sides.

Never change a subscript to balance an equation (You can only change coefficients) – If you change the subscript (formula) you are describing a different chemical. – H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula; they must go only in the front 2 NaCl is okay, but Na 2 Cl is not.

Chemical Reactions In more complicated chemical reactions, we may want to use a chart to keep track of the number of each kind of atom, CH 4 + O 2  CO 2 + H 2 O Now lets count the atoms, To balance Hydrogen. Try putting a 2 in front of the H 2 O To balance Oxygen Try putting a 2 in front of the oxygen ElementBeforeAfter C11 H42 O23 ElementBeforeAfter C11 H44 O24 ElementBeforeAfter C11 H44 O44 __

Chemical Reactions Some more practice. N 2 + H 2  NH 3 If there is a polyatomic that sticks together than you can balance it as a whole. Pb(NO 3 ) 2 + KI  PbI 2 + KNO 3 NaHCO 3 + H 2 SO 4  Na 2 SO 4 + 2H 2 O + 2CO

Practice Balancing Examples 2AgNO 3 + Cu  _Cu(NO 3 ) 2 + 2Ag 3Mg + _N 2  _Mg 3 N 2 4P + 5O 2  _P 4 O 10 2Na + 2H 2 O  _H 2 + 2NaOH CH 4 + 2O 2  _CO 2 + 2H 2 O