Evidence for a Chemical Reaction Section 7.1 Steven S. Zumdahl Susan A. Zumdahl Donald J. DeCoste Gretchen M. Adams University of Illinois at Urbana-Champaign Chapter 7 Chemical Reactions: An Introduction

Evidence for a Chemical Reaction Section To learn the signals that show a chemical reaction has occurred Objective

Evidence for a Chemical Reaction Section 7.1

Section 7.2 Chemical Equations 1.To learn to identify the characteristics of a chemical reaction 2.To learn the information given by a chemical equation Objectives

Section 7.2 Chemical Equations Chemical reactions involve a rearrangement of the ways atoms are grouped together. A chemical equation represents a chemical reaction.  Reactants are shown to the left of an arrow.  Products are shown to the right of the arrow.

Section 7.2 Chemical Equations In a chemical reaction, atoms are not created or destroyed. All atoms present in the reactants must be accounted for in the products.  Same number of each type of atom on both sides of arrow

Section 7.2 Chemical Equations Balancing a Chemical Equation Unbalanced equation

Section 7.2 Chemical Equations Balancing a Chemical Equation Balancing the equation The balanced equation CH 4 + 2O 2  CO 2 + 2H 2 O

Section 7.2 Chemical Equations Physical states of compounds are often given in a chemical equation.

Section 7.3 Balancing Chemical Equations 1.To learn to write a balanced equation for a chemical reaction Objective

Section 7.3 Balancing Chemical Equations A chemical reaction is balanced by using a systematic approach:  Write the formulas of the reactants and products to give the unbalanced chemical equation.  Balance by trial and error starting with the most complicated molecule(s).  At the end check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides).

Section 7.3 Balancing Chemical Equations Example Hydrogen gas and oxygen gas combine to form liquid water.  Write the formulas of the reactants and products to give the unbalanced chemical equation. H 2 (g) + O 2 (g)  H 2 O(l)

Section 7.3 Balancing Chemical Equations Example Hydrogen gas and oxygen gas combine to form liquid water.  Balance by trial and error starting with the most complicated molecule(s).

Section 7.3 Balancing Chemical Equations Example Hydrogen gas and oxygen gas combine to form liquid water. 2H 2 (g) + O 2 (g)  2H 2 O(l)  At the end check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides).

Section 7.3 Balancing Chemical Equations Exercise Which of the following correctly balances the chemical equation given below? There may be more than one correct balanced equation. If a balanced equation is incorrect, explain what is incorrect about it. CaO + C  CaC 2 + CO 2 I. CaO 2 + 3C  CaC 2 + CO 2 II. 2CaO + 5C  2CaC 2 + CO 2 III. CaO + (2.5)C  CaC 2 + (0.5)CO 2 IV. 4CaO + 10C  4CaC 2 + 2CO 2

Section 7.3 Balancing Chemical Equations Concept Check Which of the following are true concerning balanced chemical equations? There may be more than one true statement. I.The number of molecules is conserved. II.The coefficients tell you how much of each substance you have. III.Atoms are neither created nor destroyed. IV.The coefficients indicate the mass ratios of the substances used. V.The sum of the coefficients on the reactant side equals the sum of the coefficients on the product side.