when potassium chloride (kcl) is dissolved in water the temperature decreases. fill in the blanks to explain why this occurs. the energy required to separate the k and cl- and to separate the water molecules is — the energy produced by the attractions between the k and cl-
The Correct Answer and Explanation is :
When potassium chloride (KCl) dissolves in water, the temperature decreases because the energy required to separate the K⁺ and Cl⁻ ions and to separate the water molecules is greater than the energy produced by the attractions between the K⁺ and Cl⁻ ions and water molecules.
Explanation:
Dissolving ionic compounds like KCl in water involves three key energy changes:
- Lattice Energy (Endothermic):
Breaking the strong ionic bonds in the crystal lattice of KCl requires energy. This is an endothermic process because it absorbs energy from the surroundings. - Hydration Energy (Exothermic):
When K⁺ and Cl⁻ ions interact with water molecules, new bonds are formed between the ions and the polar water molecules. This process releases energy, making it exothermic. - Disruption of Water’s Hydrogen Bonds (Endothermic):
Water molecules must rearrange and break some of their hydrogen bonds to make space for the K⁺ and Cl⁻ ions. This also requires energy.
For KCl, the total energy required to break the ionic bonds in KCl and disrupt water’s hydrogen bonds is greater than the energy released during hydration. This results in an overall absorption of energy from the surroundings, leading to a decrease in temperature (endothermic process).
In simpler terms, the water has to “work harder” (absorb more energy) to break apart the KCl crystal and rearrange itself than it gains back when it forms new bonds with the ions. Consequently, the solution feels cooler to the touch. This phenomenon illustrates the concept of enthalpy changes during dissolution, where the sum of these energy exchanges determines whether the process is endothermic or exothermic.