Final answer:
The substance is undergoing a phase change as heat is applied; the forces holding the particles together are weakening, causing it to change from a solid to a liquid or gas, depending on the temperature. Kinetic energy increases and intermolecular forces are overcome during this process.
Step-by-step explanation:
According to the graph representing the temperature changes of a solid substance on a hot plate, as heat is added, the forces holding the particles together are breaking, which results in a change of state. When heat is applied to a solid, its kinetic energy increases, leading to more movement among the particles. This increased movement can weaken the intermolecular forces that hold the solid together, potentially causing the solid to melt into a liquid or eventually vaporize into a gas, depending on the temperature reached.
As a rule, as the temperature of a substance increases, it typically transitions from a solid to a liquid and then to a gas. This is due to the increase in entropy, where the distribution of kinetic energies among particles becomes broader and more dispersed. Additionally, heat can be absorbed without a change in temperature during a phase transition, such as melting or vaporization, which both require energy input to break intermolecular forces without increasing the substance's temperature.