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General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 6 Chemical Reactions and Quantities 6.1 Equations for Chemical Reactions © 2013 Pearson Education, Inc. Lectures Chemical Change A chemical change occurs when a substance is converted into one or more new substances. Chemical changes can be recognized by a change in color, the formation of a solid, or the formation of bubbles. © 2013 Pearson Education, Inc. Chapter 6, Section 1 A chemical change produces new substances. When silver (Ag) reacts with sulfur (S), it produces silver sulfide (Ag2S). 2 Evidence of Chemical Change © 2013 Pearson Education, Inc. Chapter 6, Section 1 3 Learning Check Identify the visible evidence of a chemical reaction in each of the following: 1. Methane gas in an outdoor heater burns with a blue flame. 2. Bleach removes stains from a shirt. 3. Bubbles of CO2 are released when baking soda is mixed with vinegar. © 2013 Pearson Education, Inc. Chapter 6, Section 1 4 Solution Identify the visible evidence of a chemical reaction in each of the following: 1. Methane gas in an outdoor heater burns with a blue flame. heat and a flame 2. Bleach removes stains from a shirt. color change (color removed) 3. Bubbles of CO2 are released when baking soda is mixed with vinegar. formation of gas (bubbles) © 2013 Pearson Education, Inc. Chapter 6, Section 1 5 Chemical Reactions A chemical reaction involves the rearrangement of atoms. produces one or more new substances. can be observed by the appearance of new physical properties. A chemical reaction forms new products with different properties. An antacid (NaHCO3) tablet in water forms bubbles of carbon dioxide (CO2). © 2013 Pearson Education, Inc. Chapter 6, Section 1 6 Writing a Chemical Equation A chemical equation tells us what substances react (reactants) and what substances are formed (products). C(s) + O2(g) reactants CO2(g) product (+) used when there is two or more products or reactants heat is used to start the reaction (s) the compound is a solid (l) the compound is a liquid (g) the compound is a gas (aq) aqueous, the compound is dissolved in water © 2013 Pearson Education, Inc. Chapter 6, Section 1 7 Equation for a Chemical Reaction © 2013 Pearson Education, Inc. Chapter 6, Section 1 8 Balanced Chemical Equations In a balanced chemical equation, the number of atoms in the reactants is equal to the number of atoms in the products for each element. © 2013 Pearson Education, Inc. Chapter 6, Section 1 9 Balancing Chemical Equations To balance a chemical equation, whole number coefficients are placed in front of the chemical formulas. coefficients in front of a molecule represent the multiple of that molecule needed in a balanced reaction. subscripts are never changed. © 2013 Pearson Education, Inc. Chapter 6, Section 1 10 Checking a Balanced Equation Reactants © 2013 Pearson Education, Inc. Products Atoms C 1 1 balanced Atoms H 4 4 Atoms O 4 4 balanced balanced Chapter 6, Section 1 11 Guide to Balancing a Chemical Equation © 2013 Pearson Education, Inc. Chapter 6, Section 1 12 Steps to Balancing a Chemical Equation Balance the following chemical reaction: Ethanol (C2H6O) burns in the presence of oxygen gas(O2) to produce steam (H2O) and carbon dioxide (CO2) gas. Step 1 Write an equation using the correct formulas of the reactants and products. © 2013 Pearson Education, Inc. Chapter 6, Section 1 13 Steps to Balancing a Chemical Equation Step 2 Count the atoms of each element in the reactants and products. Reactants Products © 2013 Pearson Education, Inc. Atoms of C 2 1 not balanced Atoms of H 6 2 Atoms of O 3 3 not balanced balanced Chapter 6, Section 1 14 Steps to Balancing a Chemical Equation Step 3 Use coefficients to balance each element. Step 4 Check the final equation to confirm it is balanced. Create a balance sheet to count atoms of each element. Reactants Products © 2013 Pearson Education, Inc. Atoms of C 2 2 Atoms of H 6 6 Atoms of O 7 7 Chapter 6, Section 1 balanced balanced balanced 15 Learning Check Determine if each equation is balanced or not. © 2013 Pearson Education, Inc. Chapter 6, Section 1 16 Solution Determine if each equation is balanced or not. Reactants Products Atoms of Na 1 3 Atoms of N 2 1 not balanced not balanced Since different numbers of Na and N atoms are present in the reactants and products, the equation is not balanced. © 2013 Pearson Education, Inc. Chapter 6, Section 1 17 Solution Determine if each equation is balanced or not. Reactants Products Atoms of C 2 2 Atoms of H 6 6 Atoms of O 1 1 balanced balanced balanced Since the same numbers of C, H and O atoms are present in the reactants and products, the equation is balanced. © 2013 Pearson Education, Inc. Chapter 6, Section 1 18 Learning Check Write a balanced equation for the reaction of nitrogen gas (N2) with hydrogen gas (H2) to form ammonia gas (NH3). © 2013 Pearson Education, Inc. Chapter 6, Section 1 19 Solution Write a balanced equation for the reaction of nitrogen gas (N2) with hydrogen gas (H2) to form ammonia gas (NH3). Step 1 Write an equation using the correct formulas of the reactants and products. Step 2 Count the atoms of each element in the reactants and products. Reactants Products © 2013 Pearson Education, Inc. Atoms of N 2 1 not balanced Atoms of H 2 3 not balanced Chapter 6, Section 1 20 Solution Write a balanced equation for the reaction of nitrogen gas (N2) with hydrogen gas (H2) to form ammonia gas (NH3). Step 3 Use coefficients to balance each element. Step 4 Check the final equation to confirm it is balanced. Reactants Products © 2013 Pearson Education, Inc. Atoms of N 2 2 Atoms of H 6 6 Chapter 6, Section 1 balanced balanced 21 Learning Check Check the balance of atoms in the following equation: 1. number of H atoms in products A. 2 B. 4 C. 8 2. number of O atoms in reactants A. 2 B. 4 C. 8 3. number of Fe atoms in reactants A. 1 © 2013 Pearson Education, Inc. B. 3 Chapter 6, Section 1 C. 4 22 Solution Check the balance of atoms in the following equation: 1. number of H atoms in products C. 8 (4H2O) 2. number of O atoms in reactants B. 4 (Fe3O4) 3. number of Fe atoms in reactants B. 3 (Fe3O4) © 2013 Pearson Education, Inc. Chapter 6, Section 1 23 Equations with Polyatomic Ions When balancing equations with polyatomic ions that remain the same on both sides of the equation, balance them as a unit. © 2013 Pearson Education, Inc. Chapter 6, Section 1 24 Balancing with Polyatomic Ions Balance the following chemical equation. Step 1 Write the equation using the correct formulas of the reactants and products. © 2013 Pearson Education, Inc. Chapter 6, Section 1 25 Balancing with Polyatomic Ions Balance the following chemical equation. Step 2 Count the atoms of each element in the reactants and products. Reactants Products © 2013 Pearson Education, Inc. Atoms of Na 3 1 PO43− ions 1 2 Atoms of Mg 1 3 Atoms of Cl 1 2 Chapter 6, Section 1 not balanced not balanced not balanced not balanced 26 Balancing with Polyatomic Ions Balance the following chemical equation. Step 3 Use coefficients to balance each element. Step 4 Check the final equation to confirm it is balanced. Reactants Products © 2013 Pearson Education, Inc. Atoms of Na 6 6 PO43− ions 2 2 Atoms of Mg 3 3 Atoms of Cl 6 6 Chapter 6, Section 1 balanced balanced balanced balanced 27 Learning Check Balance and list the coefficients from reactants to products. 1. __Fe2O3(s) + __C(s) A. 2, 3, 2,3 B. 2, 3, 4, 3 2. __Al(s) + __FeO(s) A. 2, 3, 3, 1 __Fe(s) + __CO2(g) __Fe(s) + __Al2O3(s) B. 2, 1, 1, 1 3. __Al(s) + __H2SO4(aq) A. 3, 2, 1, 2 © 2013 Pearson Education, Inc. C. 1, 1, 2, 3 __Al2(SO4)3(aq) + __H2(g) B. 2, 3, 1, 3 Chapter 6, Section 1 C. 3, 3, 3, 1 C. 2, 3, 2, 3 28 Solution Balance and list the coefficients from reactants to products. 2 3 1. __Fe 2O3(s) + __C(s) 4 3 __Fe(s) + __CO 2(g) B. 2, 3, 4, 3 2 3 2. __Al(s) + __FeO(s) 3 1 2O3(s) __Fe(s) + __Al A. 2, 3, 3, 1 3. __Al(s) + __H 2 3 2SO4(aq) __Al 1 2(SO4)3(aq) + __H 3 2(g) B. 2, 3, 1, 3 © 2013 Pearson Education, Inc. Chapter 6, Section 1 29