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Reaction Notes Part II How to balance a chemical equation Why do we need to balance a chemical equation? Sometimes, a written equation DOES NOT have equal number of reactants and products. Example: • – – – Key Thought: A balanced chemical equation gives scientists information about the relative ratio between the number of reactants and the number of products. How to “balance” a chemical equation • To balance a chemical equation, chemists use COEFFICIENTS. – • Example: – The “Easy” Method of Balancing • The acronym MINOH makes balancing chemical reactions a little easier. Title Examples – – – – – • The acronym CHO makes combustion reactions much easier to balance. Title – – – The Process of Balancing I Step 1: Step 2: • Na + Cl2 → NaCl NOTICE: When the number of products and reactants do not equal the equation must be unbalanced. The Process of Balancing II Step 3: Apply the coefficient to the equation Step 4: Distribute the coefficient to each atom. Step 5: Check to see if the products and reactants equal • Na + Cl2 → NaCl Balancing Example #2 • Fe + O2 → Fe3O2 NOTICE: Subscripts indicate how many are present to the LEFT. Balancing Example #2 • 3Fe + O2 REACTANT SIDE Fe : 1 x 3 = 3 → Fe3O2 PRODUCT SIDE Fe : 3 x 1 = 3 NOTICE: Now Fe and O2 have the same number of atoms when they react to form Fe3O2. Balancing Example #3 • C4H8 + O2 REACTANT SIDE → CO2+ H2O PRODUCT SIDE NOTICE: On the PRODUCT side, O is present in BOTH products. Balancing Example #3 • C4H8 + 6O2 REACTANT SIDE → 4CO2+ 4H2O PRODUCT SIDE NOTICE: This equation satisfies the Law of Conservation of Mass by using coefficients. Balancing Example #4 • Ag2S + KCN → REACTANT SIDE KAg(CN)2+ K2S PRODUCT SIDE K :1 + 2 NOTICE: All atoms have the same numbers in both Products and Reactants. Balancing Example #5 • Hg(OH)2 + H3PO4 → Hg3(PO4)2+ HOH REACTANT SIDE Hg: 1 OH: 2 H: 3 PO4: 1 PRODUCT SIDE NOTICE: All atoms have the same numbers in both Products and Reactants. Balancing Example #6 • I2 + HNO3 → I: H: NO3: HIO3 + NO2 + H2 IO3: H: N: O: NOTICE: All atoms have the same numbers in both Products and Reactants. Balancing Example #7 • C4H10 + Cl2 + O2 → C: H: Cl: O: CO2 + CCl4 + H2O C: H: Cl: O: NOTICE: All atoms have the same numbers in both Products and Reactants. In-Class/Homework Assignment – Homework: • Worksheet: Balancing Chemical Equations, 1-25