Lecture Presentation Chapter Chemical Reactions and Quantities Karen C Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 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 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter Readiness Key Math Skills • Calculating a Percentage (1.4C) • Solving Equations (1.4D) • Writing Numbers in Scientific Notation (1.4F) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 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) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 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 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 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 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake A chemical change produces new substances with new properties © 2016 Pearson Education, Inc Writing a Chemical Equation General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 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 Δ 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 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Symbols Used in Writing Equations General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 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 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 7.9 Energy in Chemical Reactions Almost every chemical reaction involves the loss or gain of energy When cold packs are activated, an endothermic reaction takes place Learning Goal Given the heat of reaction the rate of a reaction, calculate the loss or gain of heat for an exothermic or endothermic reaction General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Energy Units for Chemical Reactions The SI unit for energy is the joule (J) Often the unit of kilojoules (kJ) is used to illustrate the amount of energy lost or gained in a chemical reaction kilojoule (kJ) = 1000 joules (J) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Heat of Reaction The heat of reaction is the amount of heat absorbed or released during a reaction that takes place at constant pressure The change in energy occurs when • reactants interact • bonds break apart • products are formed The heat of reaction or enthalpy change, symbol ΔH, is the difference between the enthalpy of the products and enthalpy of the reactants ΔH = Hproducts − Hreactants General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Exothermic Reactions Released In an exothermic reaction, • heat is released • the energy of the products is less than the energy of the reactants • heat is a product H2(g) + Cl2(g)  2HCl(g) + 185 kJ ΔH = −185 kJ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Exothermic Reactions Released In an endothermic reaction, • heat is absorbed • the energy of the products is greater than the energy of the reactants • heat is a reactant (added) N2(g) + O2(g) + 180 kJ  2NO(g) ΔH = +180 kJ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Calculating Heat Changes The value of ΔH refers to the heat change for each substance in the balanced equation For the decomposition reaction, 2H2O(l)  2H2(g) + O2(g) ΔH = +572 kJ 2H2O(l) + 572 kJ  2H2(g) + O2(g) We can write the following conversion factors: Core Chemistry Skill Using the Heat of Reaction General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Guide to Calculations Using Heat of Reaction General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Study Check How much heat in kJ is released when nitrogen and hydrogen react to form 50.0 g of ammonia? N2(g) + 3H2(g)  2NH3(g) ΔH = −92.2 kJ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution How much heat in kJ is released when nitrogen and hydrogen react to form 50.0 g of ammonia? N2(g) + 3H2(g)  2NH3(g) ΔH = −92.2 kJ STEP State the given and needed quantities ANALYZE         Given             Need THE PROBLEM       50.0 g of NH3         heat released (kJ)         ΔH = −92.2 kJ                                      N2(g)  +  3H2(g)     2NH3(g)  General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution How much heat in kJ is released when nitrogen and hydrogen react to form 50.0 g of ammonia? N2(g) + 3H2(g)  2NH3(g) ΔH = −92.2 kJ STEP Write a plan using the heat of reaction and any molar mass needed grams of NH3 Molar  moles mass of NH3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake Heat of  kilojoules reaction © 2016 Pearson Education, Inc Solution How much heat in kJ is released when nitrogen and hydrogen react to form 50.0 g of ammonia? N2(g) + 3H2(g)  2NH3(g) ΔH = −92.2 kJ STEP Write the conversion factors including heat of reaction General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution How much heat in kJ is released when nitrogen and hydrogen react to form 50.0 g of ammonia? N2(g) + 3H2(g)  2NH3(g) ΔH = −92.2 kJ STEP Set up the problem to calculate the heat × General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake ì â 2016 Pearson Education, Inc Chemistry Link to Health: Cold Packs and Hot Packs Inside the cold pack, solid ammonium nitrate (NH4NO3) is separated from the compartment containing water When the cold pack is hit or squeezed, the compartments break and the NH4NO3 mixes with the water in an endothermic reaction H2O NH4NO3(s) + 26 kJ  NH4NO3(aq) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chemistry Link to Health: Cold Packs and Hot Packs Inside the hot pack, solid calcium chloride (CaCl2) is separated from the compartment containing water When the cold pack is hit or squeezed, the compartments break and the CaCl2 mixes with the water in an exothermic reaction H2O CaCl2(s)  CaCl2 (aq) + 82 kJ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Concept Map General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc ... 1Al2(SO4)3(aq) + 3H2(g) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life,... balanced chemical equation from the formulas of the reactants and products for a reaction; determine the number of atoms in the reactants and products General, Organic, and Biological Chemistry: Structures. .. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Guide to Balancing a Chemical Equation Core Chemistry Skill Balancing a Chemical