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Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg1

Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg1. I. Why do we need to balance chemical equations/reactions?. A. Law of Conservation of Mass. 1) Matter can be neither created nor destroyed during a chemical reaction- only changed from one form to another.

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Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg1

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  1. Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg1 I. Why do we need to balance chemical equations/reactions? A. Law of Conservation of Mass 1) Matter can be neither created nor destroyed during a chemical reaction- only changed from one form to another. 2) The total mass of the products MUST equal the total mass of the reactants. 3) There must be the same AMOUNT of each element on both sides of the chemical equation.

  2. Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg2 II. How do we balance chemical reactions? Step #1: Make SURE that you have the correct reactants & products by identifying the TYPE of reaction you have. TypeReactants: Products: barium chloride + lead nitrate barium nitrate + lead chloride DR Step #2: Make SURE that you have correct chemical formulae for the reactants & products (i.e. check your “cross-downs”) BaCl2 + Pb(NO3)4=> TypeReactants: Products: DR Ba(NO3)2+PbCl4

  3. Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg3 Step #3: Locate the most COMPLEX compound, (Complex = many elements and/or largest subscripts) & determine which ion you have the MOST of in this compound. (EXCLUDE numbers INSIDE the parentheses.) TypeReactants: Products: DR BaCl2 + Pb(NO3)4=>Ba(NO3)2+PbCl4 Step #4: Go to the OPPOSITE side of the equation to the ion that you identified in Step #3, and put a coefficient in front of that compound that when multiplied with the subscript will give you the same amount on the right & left side of that ion. TypeReactants: Products: DR BaCl2 + Pb(NO3)4=> 2Ba(NO3)2+PbCl4

  4. Chem in Context Lecture: Balancing Equations; October 27, 2006; Pg4 Just like in algebra, when you write a coefficient in front of the compound, it not ONLY changes the amount of one ion, it ALSO changes the amount of the other ion. Step #5: Go to the OPPOSITE side of the equation from where you wrote your FIRST number and find the OTHER ion that was changed. Put an appropriate coefficient in front of the compound. TypeReactants: Products: DR 2BaCl2 + Pb(NO3)4=> 2Ba(NO3)2+PbCl4 Step #6: Continue this bounce from side to side until you end up where you started. (If you need to place a 1 in front of a compound, DO NOT. A 1 is assumed like in math.) TypeReactants: Products: DR 2BaCl2 + Pb(NO3)4=> 2Ba(NO3)2+PbCl4

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