Chapter 7 Chemical Reactions Lecture Presentation Chapter 7 Chemical Reactions and Quantities Karen C. Timberlake

Chapter 7 Chemical Reactions and Quantities A dental hygienist cleans and polishes teeth and may take X-rays of the patients’ teeth. The hygienist must be knowledgeable about proper safety procedures and how to protect against disease transmission.

Chapter 7 Readiness Key Math Skills Calculating a Percentage (1.4C) Solving Equations (1.4D) Writing Numbers in Scientific Notation (1.4F)

Chapter 7 Readiness Core Chemistry Skills Counting Significant Figures (2.2) Using Significant Figures in Calculations (2.3) Writing Conversion Factors from Equalities (2.5) Using Conversion Factors (2.6) Using Energy Units (3.4) Writing Ionic Formulas (6.2) Naming Ionic Compounds (6.3) Writing the Names and Formulas for Molecular Compounds (6.5)

7.1 Equations for Chemical Reactions A chemical change occurs when a substance is converted into one or more new substances that have different formulas and different properties. Chemical reactions involve chemical changes. When iron (Fe) reacts with oxygen (O2), the product is rust, (Fe2O3). Learning Goal Write a balanced chemical equation from the formulas of the reactants and products for a reaction; determine the number of atoms in the reactants and products.

Chemical Changes A chemical change occurs when a substance is converted into one or more substances with different formulas and different properties. may be observed by the formation of bubbles, a change in color, production of a solid, or heat that is produced or absorbed. A chemical change produces new substances with new properties.

Writing a Chemical Equation

Symbols Used in Chemical Equations To write a chemical equation, an arrow separates reactants from the products (). reactants are written on the left side of the arrow; products are written on the right side of the arrow. multiple reactants or products are separated by a + sign. the delta (Δ) sign indicates heat is used to start the reaction. reactant + reactant product + product physical states of compounds are denoted in parentheses following the compound: solid (s), liquid (l), gas (g), and aqueous (aq) or dissolved in water. Δ

Symbols Used in Writing Equations

Identifying a Balanced Equation In a balanced chemical equation, no atoms are lost or gained. the number of atoms on the reactant side is equal to the number of atoms on the product side for each element.

Guide to Balancing a Chemical Equation Core Chemistry Skill Balancing a Chemical Equation

Balancing a Chemical Equation: Formation of Al2S3 STEP 1 Write an equation using the correct formulas of the reactants and products. Al(s) + S(s)  Al2S3(s) STEP 2 Count the atoms of each element in the reactants and products.

Balancing a Chemical Equation: Formation of Al2S3 STEP 3 Use coefficients to balance each element. Starting with the most complex formula, change coefficients to balance the equation. 2Al(s) + 3S(s)  Al2S3(s) STEP 4 Check the final equation to confirm it is balanced. Make sure coefficients are the lowest ratio.

Study Check State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P4(s) + 6Br2(l)  4PBr3(g) B. 2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s)

Solution State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P4(s) + 6Br2(l)  4PBr3(g)

Solution State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. B. 2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s)

Study Check Balance the chemical equation when solid Fe3O4 reacts with hydrogen gas to produce solid iron and water.

Solution Balance the chemical equation when solid Fe3O4 reacts with hydrogen gas to produce solid iron and water. STEP 1 Write an equation using the correct formulas of the reactants and products. Fe3O4(s) + H2(g)  Fe(s) + H2O(l)

Solution Balance the chemical equation when solid Fe3O4 reacts with hydrogen gas to produce solid iron and water. Fe3O4(s) + H2(g)  Fe(s) + H2O(l) STEP 2 Count the number of atoms of each element in the reactants and products.

Solution Balance the chemical equation when solid Fe3O4 reacts with hydrogen gas to produce solid iron and water. Fe3O4(s) + 4H2(g)  3Fe(s) + 4H2O(l) STEP 3 Use coefficients to balance each element.

Solution Balance the chemical equation when solid Fe3O4 reacts with hydrogen gas to produce solid iron and water. Fe3O4(s) + 4H2(g)  3Fe(s) + 4H2O(l) STEP 4 Check the final equation to confirm it is balanced.

Balancing with Polyatomic Ions

Balancing with Polyatomic Ions Balance the following chemical equation: Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) STEP 1 Write an equation using the correct formulas of the reactants and products. Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq) Unbalanced

Balancing with Polyatomic Ions STEP 2 Count the atoms of each element in the reactants and products. Balance the phosphate ion as a unit. Na3PO4(aq) + MgCl2(aq)  Mg3(PO4)2(s) + NaCl(aq)

Solution STEP 3 Use coefficients to balance each element. 2Na3PO4(aq) + 3MgCl2(aq)  Mg3(PO4)2(s) + 6NaCl(aq)

Solution STEP 4 Check the final equation to confirm it is balanced. 2Na3PO4(aq) + 3MgCl2(aq)  Mg3(PO4)2(s) + 6NaCl(aq)

Study Check Balance and list the coefficients in order from reactants to products. 1. __Fe2O3(s) + __C(s)  __Fe(s) + __CO2(g) A. 2, 3, 2, 3 B. 2, 3, 4, 3 C. 1, 1, 2, 3 2. __Al(s) + __FeO(s)  __Fe(s) + __Al2O3(s) A. 2, 3, 3, 1 B. 2, 1, 1, 1 C. 3, 3, 3, 1 3. __Al(s) + __H2SO4(aq)  __Al2(SO4)3(aq) + __H2(g) A. 3, 2, 1, 2 B. 2, 3, 1, 3 C. 2, 3, 2, 3

Solution Balance and list the coefficients in order from reactants to products. 1. B. 2, 3, 4, 3 2Fe2O3(s) + 3C(s)  4Fe(s) + 3CO2(g) 2. A. 2, 3, 3, 1 2Al(s) + 3FeO(s)  3Fe(s) + 1Al2O3(s) 3. B. 2, 3, 1, 3 2Al(s) + 3H2SO4(aq)  1Al2(SO4)3(aq) + 3H2(g)