Final answer:
The changes in phases of matter are primarily caused by the balance between the kinetic energy of the particles and the intermolecular forces. Adding heat increases the kinetic energy, causing a phase change from solid to liquid or from liquid to gas. Removing heat decreases the kinetic energy, causing a phase change from gas to liquid or from liquid to solid.
Step-by-step explanation:
The changes in phases of matter are primarily caused by the balance between the kinetic energy of the particles and the intermolecular forces. The kinetic energy keeps the particles moving and apart, while the intermolecular forces try to draw the particles together. When heat is added to a substance, it increases the kinetic energy of the particles, causing them to move faster and break free from the attractive forces, resulting in a phase change from solid to liquid or from liquid to gas. Conversely, when heat is removed, it decreases the kinetic energy, allowing the attractive forces to bring the particles closer together, causing a phase change from gas to liquid or from liquid to solid.