Final answer:
During phase changes, enthalpy (ΔH) and entropy (ΔS) change as a substance absorbs or releases energy. The enthalpy of fusion and vaporization relate to the energy involved during melting and vaporization, respectively. Entropy increases when a substance melts or vaporizes due to an increase in particle freedom and microstates.
Step-by-step explanation:
During phase changes, the enthalpy (ΔH) and entropy (ΔS) of a substance undergo characteristic alterations. When a substance transitions from solid to liquid (melting) or from liquid to gas (vaporization), both enthalpy and entropy increase. The enthalpy of fusion (ΔHfus) refers to the energy absorbed during melting, while the enthalpy of vaporization (ΔHvap) pertains to the energy required for vaporization.
Entropy, a measure of disorder or randomness in a system, reflects the freedom of particle movement and the number of microstates available. In a solid, particles are relatively fixed, presenting lower entropy compared to when the same substance is in liquid form where particles can move more freely, thus increasing entropy (ΔS > 0). Conversely, when a substance freezes, entropy decreases (ΔS < 0) as the motion of particles is restricted.
Since phase changes are isothermal, there is no temperature change during the transition. Instead, energy is either absorbed or released only to accomplish the phase change, as seen in the case of water transitioning from ice to liquid at 0°C.