Textbook Question
An ionic compound has a very negative ∆Hsoln in water (b) Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?
Ch.13 - Properties of Solutions
Chapter 13, Problem 19
(a) In Equation 13.1, which of the enthalpy terms for dissolving an ionic solid would correspond to the lattice energy? (b) Which energy term in this equation is always exothermic?
Verified step by step guidance1
Step 1: Understand the process of dissolving an ionic solid. When an ionic solid dissolves in water, the process can be broken down into three main steps: breaking the ionic lattice, separating the ions, and hydrating the ions.
Step 2: Identify the enthalpy terms involved in the dissolution process. The enthalpy change for dissolving an ionic solid (ΔH_solution) can be expressed as the sum of the lattice energy (ΔH_lattice) and the hydration energy (ΔH_hydration).
Step 3: Define lattice energy. Lattice energy is the energy required to break the ionic bonds in the solid to separate the ions, which is an endothermic process. Therefore, in Equation 13.1, the lattice energy corresponds to the enthalpy term that represents the energy needed to break the ionic lattice.
Step 4: Define hydration energy. Hydration energy is the energy released when ions are surrounded by water molecules. This process is exothermic because energy is released when new interactions between ions and water molecules are formed.
Step 5: Determine which energy term is always exothermic. In the dissolution process, the hydration energy is always exothermic because it involves the formation of ion-dipole interactions between the ions and water molecules.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Lattice Energy
Lattice energy is the energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. In the context of dissolving an ionic solid, lattice energy is the energy required to break the ionic bonds in the solid, making it a crucial factor in determining the overall energy change during dissolution.
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00:49
Lattice Energy
Enthalpy of Solution
The enthalpy of solution refers to the overall heat change that occurs when a solute dissolves in a solvent. This process can be broken down into several components, including the lattice energy, the energy required to separate solvent molecules, and the energy released when solute-solvent interactions form. Understanding these components helps in analyzing whether the dissolution process is endothermic or exothermic.
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02:34Enthalpy of Formation
Exothermic and Endothermic Processes
Exothermic processes release energy, usually in the form of heat, to the surroundings, resulting in a temperature increase in the environment. In contrast, endothermic processes absorb energy, leading to a temperature decrease. In the context of dissolving ionic solids, the formation of solute-solvent interactions can be exothermic, while breaking the lattice structure is typically endothermic, making it essential to analyze these energy changes to determine the overall thermodynamic behavior.
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01:23Endothermic & Exothermic Reactions Example 2
Related Practice
Textbook Question
When ammonium chloride dissolves in water, the solution becomes colder. (a) Is the solution process exothermic or endothermic?
Textbook Question
When ammonium chloride dissolves in water, the solution becomes colder. (b) Why does the solution form?
Textbook Question
For the dissolution of LiCl in water, ∆Hsoln = -37 kJ/mol. Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?
Textbook Question
Two nonpolar organic liquids, hexane (C6H14) and heptane (C7H16), are mixed. (a) Do you expect ∆Hsoln to be a large positive number, a large negative number, or close to zero? Explain.
Textbook Question
Two nonpolar organic liquids, hexane (C6H14) and heptane (C7H16), are mixed. (b) Hexane and heptane are miscible with each other in all proportions. In making a solution of them, is the entropy of the system increased, decreased, or close to zero, compared to the separate pure liquids?