When a solid melts, which statement is true regarding the enthalpy and entropy changes?

When a solid undergoes melting, a significant transformation occurs where the solid changes into a liquid. This process involves specific changes in enthalpy and entropy.

During melting, energy is absorbed, which means that the change in enthalpy (∆H) is positive. This energy is necessary to overcome the attractive forces that hold the molecules in the solid state. As the solid melts, the arrangement of the particles becomes less ordered, leading to an increase in disorder. This increase in disorder, or randomness, corresponds to a positive change in entropy (∆S).

In summary, when a solid melts, the system absorbs heat (indicating a positive ∆H), and the molecular disorder increases (indicating a positive ∆S), which aligns with the correct choice. Understanding these thermodynamic principles is essential in grasping how energy and disorder change during phase transitions.