Final answer:
In a phase change, a material overcomes intermolecular forces; during endothermic processes like melting, vaporization, and sublimation, energy is absorbed, while during exothermic processes such as freezing, condensation, and deposition, energy is released.
Step-by-step explanation:
When a material is changing phase, it is primarily overcoming intermolecular forces (IMFs). These forces act between the molecules within a substance. During endothermic phase transitions such as melting, vaporization, and sublimation, heat is absorbed to overcome these attractions; atoms or molecules acquire enough kinetic energy to move apart from each other. Conversely, during exothermic phase transitions, such as freezing, condensation, and deposition, heat is released as attractive forces strengthen when the particles come together.
The phase changes of a substance and the associated energy changes reflect the delicate balance between the intermolecular forces within substances and the kinetic energies of their particles. The phase at which a substance exists—solid, liquid, or gas—is determined by the temperature, which affects the average kinetic energy, and the chemical nature of the substance, which determines the strength of its intermolecular forces.