Balancing Chemical Equations Academic Success Center Science Tutoring Area Science Tutoring Area
Law of Conservation of Mass Matter cannot be created nor destroyed Therefore the number of each type of atom on each side of a chemical equation must be the same Balancing chemical equations is the process of ensuring the conservation of matter Science Science Tutoring Area
Steps for Balancing an Equation 1.Write the correct formula for each of the reactants and products 2.Verify the net ionic charge of each of the reactants and products is balanced. If it is not balance it using subscripts Example: Na +1 Cl -1 + Ca +2 SO 4-2 = Na +1 SO 4-2 + Ca +2 Cl 2-1 Science Science Tutoring Area
Steps for Balancing an Equation Note: Subscripts are only used to balance charges within a molecule not to balance the number of atoms on each side of an equation 3.Balance the number of atoms on each side of the equation by changing the coefficient in front of the different reactants and products Science Science Tutoring Area
Methods of Balancing Equations Inspection Method or Hit & Trial Method List all the elements in the reaction (it is often helpful to list them in a table of two columns - left side column for reactants and right side column for products Count the number of elements on each side Add coefficients to balance Also balance the ionic charges on each side Science Science Tutoring Area
Methods of Balancing Equations Inspection Method Example 1 K 2 O + H 2 O = KOH Each element has a count of 2 on the Reactant side (note one oxygen in each reactant) To balance add a 2 in front of the product KOH R P K 2 1 O 2 1 H 2 1 Science Tutoring Area
Methods of Balancing Equations Inspection Method Example 2 C 3 H 8 + O 2 = CO 2 + H 2 O Note the odd numbers on each side of the equation and remember the hint to multiply an odd number by 2 and then proceed To balance add a 3 to CO 2, a 4 to H 2 O and a 5 in front of O 2 on the reactant side R P C 3 1 H 8 2 O 2 3 Science Tutoring Area
Helpful Hints If an element appears in more than 1 place on one side of the equation balance it last Ex. C 6 H 12 O 6 (s) + O 2 (g) = CO 2 (g) + H 2 O(l) In this example oxygen is in two places on the products side of the equation so leave oxygen for last Start with carbon, then hydrogen and finish up with oxygen Science Science Tutoring Area
Helpful Hints If a fraction will balance the equation, multiply the entire equation (both reactants and products) by the inverse of the fraction to eliminate the fraction C 3 H 7 S(l) + O 2 (g) = CO 2 + H 2 O(l) + SO 2 Placing 7/2 in front of water will balance the hydrogen on the product side but it is best to multiple the entire equation through by 2 to remove the denominator of the fraction to have the final balanced equation with whole number coefficients Science Science Tutoring Area
Helpful Hints If all coefficients are divisible by a small whole number, divide to get the simplest equation 4C + 2O 2 = 4CO simplified is 2C + O 2 = 2CO Science Science Tutoring Area
Helpful Hints continued If polyatomic ions are the same on the reactant side as the product side, balance the polyatomic ion as one group or one ion 2(NH4)3PO4(aq) + 3 CaCl2 Ca3(PO4)2(s) + 6 NH4Cl(aq) 24 hydrogens, 6 nitrogens, 2 phosphoruses, 8 oxygens, 3 calciums, 6 chlorines 24 hydrogens, 6 nitrogens, 2 phosphoruses, 8 oxygens, 3 calciums, 6 chlorines 6 ammoniums, 2 phosphates, 3 calciums, 6 chlorides 6 ammoniums, 2 phosphates, 3 calciums, 6 chlorides If an odd number of atoms appear on one side of the equation multiply the odd number by 2 and continue to balance the equation Balance monatomic or diatomic elements last Balance H 2 O last if it is in the equation Science Science Tutoring Area
Examples Calcium carbonate + sulfuric acid yields calcium sulfate + carbon dioxide + water CaCO3 + H2SO4 = CaSO4 + CO2 + H20 Sodium chloride + ammonia gas + water + carbon dioxide produces ammonium chloride + sodium bicarbonate NaCl + NH3 + H2O + CO2 = (NH4)Cl + NaHCO3 Magnesium + water yields magnesium hydroxide + hydrogen gas Mg + H2O = MgOH + H2 Science Science Tutoring Area