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BALANCING CHEMICAL EQUATIONS Chapter 6.5 DAY 1 & 2

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Word equations or formula (skeleton) equations need to be balanced. The number of atoms of one element on the reactant side of an equation must equal the number of atoms of that same element on the product side of an equation.

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LAW OF CONSERVATION OF MASS States: the total mass of atoms must be the same on both sides of an equation. Meaning –> the mass of the reactants equals the mass of the products. The same total number of each atom = same total atomic mass

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How to count atoms review Using Black line 6.5a, we will review counting atoms before we learn the skill of balancing equations.

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1) The symbol of an element represents one atom of that element Example: Ca = 1 atom 2) A subscript is a number written at the lower right corner after the symbol of an element. If there is more than one atom of the element in the molecule, then a subscript is used to indicate the number of atoms. Example: N 2 = 2 atoms

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3) A subscript outside a bracket multiplies all the elements inside the brackets. Example: Ba 3 (PO 4 ) 2 Barium – 3 atoms Phosphorus – 2 atoms Oxygen – 8 atoms 4a) A coefficient is a number written a chemical symbol and indicates the number of atoms of that element. 4a) A coefficient is a number written in front of a chemical symbol and indicates the number of atoms of that element. Example: 3C = 3 carbons

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4b) A coefficient is a number written a chemical formula and indicates the number of molecules of that compound. 4b) A coefficient is a number written in front of a chemical formula and indicates the number of molecules of that compound. 2H 2 O = Hydrogen 2 x 2 = 4 atoms, Oxygen 1 x 2 = atoms 2H 2 O = Hydrogen 2 x 2 = 4 atoms, Oxygen 1 x 2 = atoms NOTE: A coefficient multiplies the number of atoms of each element in the formula. 4Cu(NO 3 ) 2 = Copper 1 x 4 = atoms, Nitrogen 1 x 2 x 4 = 8 atoms, Oxygen 3 x 2 x 4 = 24 atoms

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LETS BALANCE EQUATIONS STEP 1 – Write the formula equation of the reaction. Example: CH 4 + O 2 CO 2 + H 2 O

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STEP 2 – Count the number of atoms of each type on the reactants side and on the products side reactants products reactants products O – 2 O - 3 O – 2 O - 3 C – 1 C - 1 C – 1 C - 1 H – 4 H – 2 H – 4 H – 2

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3) Multiply each of the formulas by an appropriate coefficient to balance the numbers of atoms CH 4 + 2 O 2 CO 2 + 2 H 2 O 4) Count atoms on each side to verify. reactants products O – 4 O - 4 O – 4 O - 4 C – 1 C - 1 C – 1 C - 1 H – 4 H – 4 H – 4 H – 4

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GROUP PRACTICE 1) hydrogen and oxygen produce water 2) calcium and chlorine make calcium chloride 3) aluminum and oxygen produce aluminum oxide 4) copper and iron(III) oxide make iron and copper(I) oxide

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HOMEWORK 1. How to Count Atoms Review 2. PAGE 229 # 2, 3ade 3. Balancing Equations Worksheet

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