Balancing Chemical Equations
Word Equations Example Methane + Oxygen Carbon dioxide + Water The arrow means yields, gives, or reacts to produce.
Chemical Equations A shorthand way to describe a chemical reaction using chemical symbols and formulae Three Parts to a Chemical Equation Reactants substances present before the reaction Yield Arrow indicates the direction of a reaction Products substances present after the reaction
Chem. Equations – cont’d Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium or… magnesium oxide reacting with carbon yields carbon monoxide and magnesium
Chemical Equations – cont’d Coefficient – (large) # in front of an element applies to all elements in the group to the right of it ex: 4C 4 carbon atoms ex: 5KI 5 potassium atoms & 5 iodine atoms ex: 4SO4 4 Sulfur atoms & 16 Oxygen atoms (4x4)
Chemical Equations – cont’d Subscript – (small) # to the lower right of an element applies only to the element it is attached to if outside of parentheses [(XY)3] applies to everything inside of parentheses ex: H2 2 hydrogen atoms ex: CO2 1 carbon atom, 2 oxygen atoms ex: (SO4)3 3 Sulfur atoms (1x3), 12 Oxygen atoms (4x3)
Chemical Equations - cont’d Try this: Al2(SO4)3 Aluminum? 2 atoms Sulfur? 3 atoms Oxygen? 12 atoms (4x3)
Balancing Chem Equations Law of Conservation of Matter matter is neither created nor destroyed in a chemical reaction, it is conserved ie, if you begin a reaction with 5 atoms of Hydrogen, you must end up with 5 atoms of Hydrogen
Balancing – cont’d Al + S Al2S3 2Al + 3S Al2S3 Balanced = same # of each element on each side Al + S Al2S3 2Al + 3S Al2S3 Unbalanced Balanced
Balanced or Unbalanced? C3H8 + 5O2 4H2O + 3CO2 Carbon? = 3 vs 3 Hydrogen? = 8 vs 8 Oxygen = 10 vs 10 (4 + 6) Is it balanced? Yes.
Balanced or Unbalanced? Fe3O4 + H2 Fe + H2O Iron = 3 vs 1 Oxygen = 4 vs 1 Hydrogen = 2 vs 2 Is it balanced? No. So, now what?
Balancing a Chemical Reaction Set up two columns: labeled “reactants” &“products.” Identify & record reacting elements on the left. Record elements in the SAME ORDER on the right. Count & Record # of each reacting element. Count & Record # of each element produced. Unequal? Balance Coefficients. [can’t change subscripts] you can treat Polyatomic Ions as one if they appear on both sides of the equation like (SO4) in parentheses change your greatest inequality first leave solitary elements for last
Practice Fe3O4 + H2 Fe + H2O
Never Change a subscript to balance an equation. If you change the formula you are describing a different reaction. H2O is a different compound than H2O2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.
Practice On your worksheet, complete the two problems on the front of your sheet. ____H2 + ____O2 ____H2O ____Cl2 + ____NaBr ____Br2 + ____NaCl 2 1 2 1 2 1 2