Balancing Chemical Reactions Chemistry Balancing Chemical Reactions

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Balanced Chemical Equations …… A balanced equation has the same number of each element _________

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. H2 + O2  H2O How many oxygen atoms are on the right? _________ How many oxygen atoms are on the left? 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** 2 2

Rules for balancing: Assemble the _________ _________for all the reactants and products, using “+” and “→” Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - __________ (hint: I prefer to save O until the very last) _____________________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. H2O is a different compound than H2O2 _________ put a coefficient in the middle of a formula; they must go only in the _________ _____ NaCl is okay, but Na______Cl is not.

Chemical Reactions Element Before After C 1 H 4 2 O 3 Element Before In more complicated chemical reactions, we may want to use a chart to keep track of the number of each kind of atom, CH4 + O2  CO2 + H2O Now lets count the atoms, To balance Hydrogen. Try putting a 2 in front of the H2O To balance Oxygen Try putting a 2 in front of the oxygen Element Before After C 1 H 4 2 O 3 Element Before After C 1 H 4 O 2 _ _ Element Before After C 1 H 4 O

Some more practice. N2 + H2  NH3 Pb(NO3)2 + KI  PbI2 + KNO3 If there is a polyatomic that sticks together than you can balance it as a whole. Pb(NO3)2 + KI  PbI2 + KNO3 NaHCO3 + H2SO4  Na2SO4 + H2O + CO2 _ _ _ _ _ _ _

Practice Balancing Examples _AgNO3 + _Cu ® _Cu(NO3)2 + _Ag _Mg + _N2 ® _Mg3N2 _P + _O2 ® _P4O10 _Na + _H2O ® _H2 + _NaOH _CH4 + _O2 ® _CO2 + _H2O