What happened to the solid substance in the energy box as most heat was added. Describe what activity in the molecules and the shape of the graph?

As more heat was added, the solid substance melted into a liquid and then evaporated into a gas. The molecules in the substance gained energy, vibrated more vigorously, and eventually overcame the intermolecular forces holding them together as a solid. The graph would show an initial increase in temperature as the solid heated up, followed by a plateau during the phase change from solid to liquid, and then another increase as the liquid turned into a gas.