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BALANCING CHEMICAL EQUATIONS A BALANCED EQUATION • Atoms cant be created or destroyed • Law of Conservation of Mass • All the atoms we start with we must end up with • A balanced equation has the same number of each element on both sides of the equation (reactant and product sides). COUNTING ATOMS • 2H2 + O2 • Reactants 2H2O Product • Subscript: (numbers below) • indicates how many atoms of an element. • Coefficient (numbers in front) • Indicates how many molecules of a compound • (multiplies the number of atoms of each element in the compound) Chemical Formula Counting up Atoms Let’s Practice • NH3 1 • _____ 3 • _____ 1 • _____ • NaCl 1 • _____ 1 • _____ 1 • _____ atoms of Nitrogen atoms of Hydrogen molecules/moles of NH3 atoms of Sodium atoms of Chlorine molecule/moles of NaCl PRACTICE AGAIN • 8NaCl 8 atoms of Sodium • _____ 8 atoms of Chlorine • _____ 8 molecule/moles of NaCl • _____ • 3NH3 • ____ 3 atoms of Nitrogen 9 atoms of Hydrogen • ____ 3 molecule/moles of NH3 • ____ • Ca(NO3)2 1 atoms of Calcium • _____ 2 atoms of Nitrogen • _____ 6 atoms of Oxygen • _____ 1 molecule/moles of Ca(NO3)2 • _____ RULES FOR BALANCING Write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements (make them same amount on reactant and product sides) one at a time by adding coefficients (the numbers in front). Check to make sure it is balanced. 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. EXAMPLE H2 + O2 H2O Make a table to keep track of where you are EXAMPLES • CH4 + O2 CO2 + H2O • AgNO3 + Cu Cu(NO3)2 + Ag • Mg + N2 Mg3N2 • P + O2 P4O10 • Na + H2O H2 + NaOH ANSWERS TO EXAMPLES • CH4 + 2O2 CO2 + 2H2O • 2AgNO3 + Cu Cu(NO3)2 + 2Ag • 3Mg + N2 Mg3N2 • 4P + 5O2 P4O10 • 2Na + 2H2O H2 + 2NaOH