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Chapter 7 Chemical Reactions 7.2 Chemical Equations Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 1 Chemical Equations A chemical equation • Gives the chemical formulas of the reactants on the left of an arrow and the products on the right. Reactants Product O2(g) C(s) Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 2 CO2 (g) Chemical Equations are Balanced In a balanced chemical reaction • Atoms are not gained or lost. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 3 Chemical Equations are Balanced In a balanced chemical reaction • The number of reactant atoms is equal to the number of product atoms. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Symbols Used in Equations Symbols are used in equations to show Table 7.2 • The states of the reactants. • The states of the products. • The reaction conditions. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings 5 A Balanced Chemical Equation In a balanced chemical equation, • There must be the same number of each type of atom on the reactant and on the product sides of a balanced equation. • Numbers called coefficients are used in front of one or more formulas. Al + S Al2S3 Not Balanced Al2S3 Balanced coefficients 2Al + 3S 6 2Al = 2Al 3S = 3S Learning Check State the number of atoms of each element on the reactant and on the product sides of the equations: A. P4(s) + 6Br2(l) → 4 PBr3(g) B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s) 7 Solution State the number of atoms of each element on the reactant and on the product sides of the equations: A. P4(s) + 6Br2(l) → 4PBr3(g) 4P 4P 12 Br 12 Br B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s) 2 Al 2 Al 2 Fe 2 Fe 3O 3O 8 Learning Check Determine if each equation is balanced or not. A. Na(s) + N2(g) → NaN3(s) B. C2H4(g) 9 + H2O(l) → C2H5OH(l) Solution Determine if each equation is balanced or not. A. Na(s) + N2(g) → NaN3(s) No. 2N on reactant side, 3N on product side. B. C2H4(g) + H2O(l) → C2H5OH(l) Yes. 2 C = 2C 6H = 6H 1O = 1O 10