melting curve

In physics, the melting curve represents the equilibrium between a solid and a liquid. When this curve is crossed from solid to liquid, the substance melts, accompanied by an abrupt change in its properties. The melting point is the specific temperature at which a pure solid and its liquid form can coexist in equilibrium. As heat is added to a solid, its temperature rises to the melting point, where further heat input transforms it into a liquid without changing the temperature.12

The melting temperature is generally not significantly affected by pressure, unlike the vapor-pressure curve. However, for a few substances like water and bismuth, the melting curve has a negative slope, meaning the melting temperature decreases with increasing pressure. This phenomenon is why ice floats, as solid water is less dense than liquid water.13