# Unit 3. Chemical Reactions 3.3 How do we balance a chemical reaction?

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Unit 3. Chemical Reactions 3.3 How do we balance a chemical reaction?
February 8, 2010 AIM: How do we balance chemical reactions in order to obey the law of conservation of mass? DO NOW: MR #3 An element that has a low first ionization energy and good conductivity of heat and electricity is classified as a (1) metal (3) nonmetal (2) metalloid (4) noble gas J CHOICE LOW IONIZATION ENERGY? GOOD CONDUCTIVITY OF HEAT AND ELECTRICITY? METAL NONMETAL METALLOID NOBLE GAS Check the TABLE S LOW YES THINK: copper wires Periodic Trends? HIGH NO SOME HIGH SOME LOW SOME YES SOME NO These are nonmetals already….don’t waste your time!

HOW DO WE BALANCE EQUATIONS?
C(s) + O2(g) → CO2(g) Step 1. Check that an equal amount of an element appears in the reactants that does in the products Element Reactants Products C 1 1 O 2 2 Step 2. If not equal add coefficients THIS IS A BALANCED EQUATION Step 3. Check that the equation is balanced after you add coefficients.

LET’S TRY SOME 2 x 2 = 4 2 x 2 = 4 2 1 x 2 = 2 H2(g) + O2(g) → H2O(g)
Element Reactants Products H O 2 x 2 = 4 2 x 2 = 4 2 1 x 2 = 2 Not equal so we must add COEFFICIENTS!

LET’S TRY SOME 1 x 2 = 2 1 1 x 2 = 2 1 3 x 2 = 6 2 x 3 = 6 2 2 3 x 2
KClO3  KCl + O2 3 Reactants Products K Cl O 1 x 2 = 2 1 x 2 = 2 1 x 2 = 2 1 x 2 = 2 3 x 2 = 6 2 x 3 = 6

Complete the Independent Practice
-IP will be collected at the end of class!!! WORK ON UNIT 1 in your HOMEWORK PACKET UNIT 1 completion will be check on Monday at the beginning of class

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