General Chemistry II: Atomic and Molecular Structure Fall 2024 PDF

General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Unit 3: Structural Properties Enthalpies of solution FOCUS: Understand what is the enthalpy change of solution, how it...

General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Unit 3: Structural Properties Enthalpies of solution FOCUS: Understand what is the enthalpy change of solution, how it is calculated Prof. German Perez  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Objectives 3.2.4 Describe the unique physical properties of water. 3.2.5 Describe the typical physical properties of ionic compounds. 3.2.6 Use a thermodynamic cycle to describe the solution process of an ionic compound and to explain the factors affecting the enthalpy of solution.** 3.2.7 Describe the solubility of an ionic compound in terms of the lattice energy, enthalpy of solution and the entropy change for the solution process.** 2  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Water, the Universal Solvent Water is a polar compound, i.e. one that has a distribution of charge High Specific Heat Capacity High Heat of Vaporization Cohesion and Adhesion Density Anomaly Excellent Solvent 3  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Solubility of Ionic Compounds Lattice energy is the energy change Hydration energy is the amount of upon formation of one mole of a energy released when one mole of crystalline ionic compound from its ions in gaseous state undergoes constituent ions in gaseous state hydration 4  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Dissolution of an Ionic Substance https://www.youtube.com/watch?v=CLHP4r0E7hg 5  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Steps Involved in the Formation of a Liquid Solution 1. Expand the solute (i.e. lattice energy) Separate the solute into its individual components 2. Expand the solvent (i.e. IMF) Overcome intermolecular forces in the solvent to make room for the solute 3. Allow the solute and solvent to interact to form the solution (i.e. hydration energy) Copyright © Cengage Learning. All rights reserved 6  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Steps Involved in the Formation of a Liquid Solution (continued) Steps 1 and 2 are endothermic Forces must be overcome to expand the solute and solvent Step 3 is often exothermic Copyright © Cengage Learning. All rights reserved 7  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Enthalpy (Heat) of Solution (ΔHsoln) Enthalpy change associated with the formation of the solution is the sum of the ΔH values for the steps: ΔHsoln can have a positive sign when energy is absorbed or a negative sign when energy is released H soln = H1 + H 2 + H 3 Copyright © Cengage Learning. All rights reserved 8  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Figure 11.2 - Heat of Solution Hsoln has a negative sign if Step 3 Hsoln has a positive sign if Steps 1 releases more energy than that and 2 require more energy than is required by Steps 1 and 2 released in Step 3  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Factors That Favor a Process Increase in probability of the mixed state when the solute and solvent are placed together Processes that require large amounts of energy tend not to occur Like dissolves like Copyright © Cengage Learning. All rights reserved 10  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Table 11.3 - The Energy Terms for Various Types of Solutes and Solvents  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Hydration enthalpies Enthalpy of hydration, ΔHhyd, of an ion is the amount of heat released when a mole of the ion dissolves in a large amount of water forming an infinitely dilute solution in the process: 12  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Using Born Haber Cycles Suppose we want to determine the enthalpy of solution of calcium chloride 13  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Examples 14  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Examples What about MgCl2? 15  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Exercise Decide whether liquid hexane (C6H14) or liquid methanol (CH3OH) is the more appropriate solvent for the substances grease (C20H42) and potassium iodide (KI)  General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 Exercise For each of the following pairs, predict which substance would be more soluble in water NH3 CH3COOH General Chemistry II: Atomic and Molecular Structure Chemistry Department FALL 2024 18