Write out the chemical reaction whose enthalpy is the heat of fusion of sodium chloride, NaCl
The Correct Answer and Explanation is:
Correct Chemical Reaction (Heat of Fusion of NaCl): NaCl(s)→NaCl(l)\text{NaCl(s)} \rightarrow \text{NaCl(l)}NaCl(s)→NaCl(l)
Explanation
The heat of fusion refers to the amount of energy required to change a substance from the solid phase to the liquid phase at its melting point without changing its temperature. For sodium chloride (NaCl), the heat of fusion is the energy needed to overcome the strong ionic forces that hold its ions in the rigid lattice structure of the solid.
The reaction that represents this process involves a physical transformation of sodium chloride from solid to liquid form. It does not involve a chemical change or a rearrangement of atoms, but a change in the physical state. This transformation is expressed simply as: NaCl(s)→NaCl(l)\text{NaCl(s)} \rightarrow \text{NaCl(l)}NaCl(s)→NaCl(l)
This equation shows that solid sodium chloride (NaCl(s)) absorbs a specific amount of energy, known as the enthalpy of fusion, to become liquid sodium chloride (NaCl(l)). The heat absorbed is typically measured in kilojoules per mole (kJ/mol).
Sodium chloride has a high melting point, around 801°C, due to the strong electrostatic attraction between its positively charged sodium ions (Na⁺) and negatively charged chloride ions (Cl⁻). These forces must be overcome to allow the ions to move freely in the liquid state. This requires a significant input of thermal energy.
This phase change is classified as an endothermic process, meaning it absorbs energy from the surroundings. During the process, the temperature of sodium chloride remains constant until the entire solid has melted, even though energy continues to be added.
Understanding this heat of fusion is important in thermodynamics and material science, especially when designing industrial processes that involve high-temperature melting or purification of ionic compounds like sodium chloride.
