General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 6.1 Equations for Chemical Reactions Chapter 6 Chemical Reactions and Quantities © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 6, Section 1 2 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. A chemical change produces new substances. When silver (Ag) reacts with sulfur (S), it produces silver sulfide (Ag 2 S).

© 2013 Pearson Education, Inc. Chapter 6, Section 1 3 Evidence of Chemical Change

© 2013 Pearson Education, Inc. Chapter 6, Section 1 4 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 CO 2 are released when baking soda is mixed with vinegar.

© 2013 Pearson Education, Inc. Chapter 6, Section 1 5 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 CO 2 are released when baking soda is mixed with vinegar. formation of gas (bubbles)

© 2013 Pearson Education, Inc. Chapter 6, Section 1 6 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 (NaHCO 3 ) tablet in water forms bubbles of carbon dioxide (CO 2 ).

© 2013 Pearson Education, Inc. Chapter 6, Section 1 7 Writing a Chemical Equation A chemical equation tells us what substances react (reactants) and what substances are formed (products).

© 2013 Pearson Education, Inc. Chapter 6, Section 1 8 Equation for a Chemical Reaction

© 2013 Pearson Education, Inc. Chapter 6, Section 1 9 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 10 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 11 Checking a Balanced Equation Atoms C11 Atoms H44 Atoms O44 Reactants Products balanced

© 2013 Pearson Education, Inc. Chapter 6, Section 1 12 Guide to Balancing a Chemical Equation

© 2013 Pearson Education, Inc. Chapter 6, Section 1 13 Steps to Balancing a Chemical Equation Balance the following chemical reaction: Ethanol (C 2 H 6 O) burns in the presence of oxygen gas(O 2 ) to produce steam (H 2 O) and carbon dioxide (CO 2 ) gas. Step 1 Write an equation using the correct formulas of the reactants and products.

© 2013 Pearson Education, Inc. Chapter 6, Section 1 14 Steps to Balancing a Chemical Equation Step 2 Count the atoms of each element in the reactants and products. Reactants Products not balanced balanced Atoms of C21 Atoms of H62 Atoms of O33

© 2013 Pearson Education, Inc. Chapter 6, Section 1 15 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 balanced Atoms of C22 Atoms of H66 Atoms of O77

© 2013 Pearson Education, Inc. Chapter 6, Section 1 16 Learning Check Determine if each equation is balanced or not.

© 2013 Pearson Education, Inc. Chapter 6, Section 1 17 Solution Determine if each equation is balanced or not. Reactants Products not balanced Since different numbers of Na and N atoms are present in the reactants and products, the equation is not balanced. Atoms of Na13 Atoms of N21

© 2013 Pearson Education, Inc. Chapter 6, Section 1 18 Solution Determine if each equation is balanced or not. Reactants Products balanced Since the same numbers of C, H and O atoms are present in the reactants and products, the equation is balanced. Atoms of C22 Atoms of H66 Atoms of O11

© 2013 Pearson Education, Inc. Chapter 6, Section 1 19 Write a balanced equation for the reaction of nitrogen gas (N 2 ) with hydrogen gas (H 2 ) to form ammonia gas (NH 3 ). Learning Check

© 2013 Pearson Education, Inc. Chapter 6, Section 1 20 Write a balanced equation for the reaction of nitrogen gas (N 2 ) with hydrogen gas (H 2 ) to form ammonia gas (NH 3 ). 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 not balanced Solution Atoms of N21 Atoms of H23

© 2013 Pearson Education, Inc. Chapter 6, Section 1 21 Write a balanced equation for the reaction of nitrogen gas (N 2 ) with hydrogen gas (H 2 ) to form ammonia gas (NH 3 ). Step 3 Use coefficients to balance each element. Step 4 Check the final equation to confirm it is balanced. Reactants Products balanced Solution Atoms of N22 Atoms of H66

© 2013 Pearson Education, Inc. Chapter 6, Section 1 22 Check the balance of atoms in the following equation: 1. number of H atoms in products A. 2B. 4C number of O atoms in reactants A. 2B. 4C number of Fe atoms in reactants A. 1B. 3C. 4 Learning Check

© 2013 Pearson Education, Inc. Chapter 6, Section 1 23 Check the balance of atoms in the following equation: 1. number of H atoms in products C. 8 (4H 2 O) 2. number of O atoms in reactants B. 4 (Fe 3 O 4 ) 3. number of Fe atoms in reactants B. 3 (Fe 3 O 4 ) Solution

© 2013 Pearson Education, Inc. Chapter 6, Section 1 24 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 25 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 26 Balancing with Polyatomic Ions Balance the following chemical equation. Step 2 Count the atoms of each element in the reactants and products. Reactants Products not balanced Atoms of Na31 PO 4 3− ions12 Atoms of Mg13 Atoms of Cl21

© 2013 Pearson Education, Inc. Chapter 6, Section 1 27 Balancing with Polyatomic Ions Step 3 Use coefficients to balance each element. Step 4 Check the final equation to confirm it is balanced. Atoms of Na66 PO 4 3− ions22 Atoms of Mg33 Atoms of Cl66 Balance the following chemical equation. ReactantsProducts balanced

© 2013 Pearson Education, Inc. Chapter 6, Section 1 28 Balance and list the coefficients from reactants to products. 1. __Fe 2 O 3 (s) + __C(s) __Fe(s) + __CO 2 (g) A. 2, 3, 2,3 B. 2, 3, 4, 3 C. 1, 1, 2, 3 2. __Al(s) + __FeO(s) __Fe(s) + __Al 2 O 3 (s) A. 2, 3, 3, 1 B. 2, 1, 1, 1 C. 3, 3, 3, 1 3. __Al(s) + __H 2 SO 4 (aq) __Al 2 (SO 4 ) 3 (aq) + __H 2 (g) A. 3, 2, 1, 2 B. 2, 3, 1, 3 C. 2, 3, 2, 3 Learning Check

© 2013 Pearson Education, Inc. Chapter 6, Section 1 29 Balance and list the coefficients from reactants to products. 1. __Fe 2 O 3 (s) + __C(s) __Fe(s) + __CO 2 (g) B. 2, 3, 4, 3 2. __Al(s) + __FeO(s) __Fe(s) + __Al 2 O 3 (s) A. 2, 3, 3, 1 3. __Al(s) + __H 2 SO 4 (aq) __Al 2 (SO 4 ) 3 (aq) + __H 2 (g) B. 2, 3, 1, Solution