key term - Enthalpy of fusion

Definition

Enthalpy of fusion is the heat energy required to change a substance from solid to liquid at constant pressure and temperature. This thermodynamic property is crucial in understanding phase changes and is represented as a positive value, reflecting the energy needed to overcome intermolecular forces holding the solid structure together.

5 Must Know Facts For Your Next Test

1. The enthalpy of fusion is specific to each substance and varies significantly between materials due to differences in intermolecular forces.
2. When a solid melts, it absorbs heat equal to its enthalpy of fusion, which is why ice feels cold when it melts in your hand.
3. The enthalpy of fusion is often expressed in units of kJ/mol, indicating the energy required per mole of substance.
4. In phase diagrams, the enthalpy of fusion is represented at the boundary between solid and liquid phases, highlighting the energy input needed for melting.
5. The process of melting is endothermic, meaning it requires energy input, which corresponds directly to the enthalpy of fusion value.

Review Questions

• How does the enthalpy of fusion relate to the concept of phase changes in substances?
  • The enthalpy of fusion directly correlates with the phase change from solid to liquid, as it quantifies the energy required for this transition. When a solid absorbs heat equal to its enthalpy of fusion, it breaks free from its structured arrangement, becoming a liquid. This relationship is crucial for understanding how substances behave when they transition between states, highlighting the role of energy in these processes.
• Compare and contrast the enthalpy of fusion and latent heat during phase changes.
  • While both the enthalpy of fusion and latent heat refer to energy changes during phase transitions, they focus on different aspects. The enthalpy of fusion specifically measures the energy required to convert a solid into a liquid at its melting point. In contrast, latent heat encompasses all phase changes, including melting and boiling, representing the total energy absorbed or released during these transformations. Understanding both concepts helps clarify how energy interactions influence material behavior.
• Evaluate the implications of enthalpy of fusion values on material selection in engineering applications involving temperature changes.
  • Understanding the enthalpy of fusion values is critical in engineering as it influences material selection for applications that involve thermal management. Materials with high enthalpy of fusion values can absorb significant amounts of heat without substantial temperature changes, making them ideal for thermal buffers or heat storage systems. Conversely, materials with lower values might be chosen for rapid heating or cooling applications. Evaluating these properties ensures that engineers can design systems that efficiently manage thermal transitions while maintaining structural integrity.

Related terms

Phase Change: A transition of a substance from one state of matter to another, such as solid to liquid or liquid to gas.

Latent Heat: The heat absorbed or released during a phase change without a change in temperature.

Melting Point: The specific temperature at which a solid becomes a liquid under standard atmospheric pressure.