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Balancing Chemical Equations Chapter 7

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What is Balancing? Making sure there are equal numbers of each type of atom on each side of a chemical reaction Reactants = products Why do this???????

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Law of Conservation of Mass Matter is neither created or destroyed in a chemical reaction. What does this mean? Atoms are not created or destroyed during a chemical reaction.

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-The number and types of atoms do not change -- atoms are just rearranged mass of the = mass of the reactants products There must be the same number of each element on both sides of the equation. reactantsproducts

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When balanced. # of reactant atoms = # product atoms If you put 3 oxygen in on the left side, then you must get out 3 oxygen on the right side.

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To BALANCE: 1. Only change Coefficients 2. Do not change the subscripts. (Only change the numbers in front of each compound or atom.)

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Steps for Balancing Equations 1.Write the formulas for the reactants and products, put in equation form (skeleton equation with no coefficients) – might be done for you. 2.Count the number of atoms of each element on both sides of the yield arrow. 3.Balance atoms by adding coefficients (prefixes) to appropriate formulas 4.Check work by recounting atoms of each elements.

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Example1:Ca + O 2 → CaO (calcium) (Oxygen gas) (Calcium Oxide) ReactantsProducts Calcium11 Oxygen21 - Calcium is balanced, oxygen is not - Use coefficients to balance the number of oxygen atoms - Now the calciums are unbalanced so need another coefficient 22 2 2 2

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Example2:H 2 + O 2 → H2OH2O ReactantsProducts Hydrogen22 Oxygen21 - Hydrogen is balanced, oxygen is not - Use coefficients to balance the number of oxygen atoms - Now the hydrogens are unbalanced so so need another coefficient. 22 2 44

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Example2:NaCl → Na + Cl 2 ReactantsProducts Sodium11 Chlorine12 - Sodium is balanced, chlorice is not - Use coefficients to balance the number of chlorine atoms - Now the sodium are unbalanced so so need another coefficeint. 22 22 2

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Example 3:Fe + O 2 → Fe 2 O 3 ReactantsProducts Iron12 Oxygen23 Both the iron and oxygen are unbalanced. Tip: Sometimes it helps to balance the oxygen atoms first. The least common multiple between 2 and 3 is 6 Now the Iron has to be balanced 23 66 4 4 4

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