Melting vs Freezing Point
Matter comes in different states, the distinctive forms and phases that it acquires or assumes. It comes in a solid state which gives it a fixed volume and shape; in a liquid state which gives it a fixed volume but does not have a definite shape, and it has to adapt to the shape of its container; and a gas state which allows it to expand and occupy any volume available.
The state of matter depends on the pressure and temperature that are applied to it which allows its transition from one form or state to another with each decrease or increase in the pressure or temperature. Matter can be changed from a solid state to a liquid state by melting, and it can be changed from a liquid to a solid by freezing.
The melting point and freezing point of matter or a substance varies according to its components. The melting point of a substance is defined as the temperature at which a solid, when given enough heat, is turned into liquid depending on the purity of the substance and the pressure that is applied to it.
The freezing point of a substance is defined as the temperature at which matter or a substance is changed from its liquid state into solid. For some substances, the melting point is equal to or the same as its freezing point. For mixtures and organic compounds, however, the freezing point is lower than the melting point.
The melting point is considered as a characteristic property of a substance while the freezing point is not because there are substances that can be supercooled or cooled beyond the freezing point without the formation of solid crystals.
At the melting point, the solid and liquid phases of a substance are in equilibrium, that is, the chemical reaction and its reverse are at equal rates and do not change. The melting point of a substance depends largely on the standard atmospheric pressure while pressure only has a little effect on a substance’s freezing point.
Water, which is a pure substance, has the same melting and freezing points. But when it is mixed with other substances, it has a slower melting or freezing point. The melting point of a substance is the basis for the identification of pure substances and compounds.
Summary:
1.The melting point is the temperature at which a solid is changed into a liquid by applying heat and pressure while the freezing point is the temperature at which a liquid is changed into a solid.
2.While most substances, especially pure substances, have the same melting and freezing points. Some substances, like mixtures and compounds, have lower freezing points than their melting points.
3.The melting point of a substance depends on the standard atmospheric pressure while pressure has a minor effect on the freezing point of a substance.
4.The melting point of a substance is the basis for the determination of its purity and the identification of compounds while the freezing point is not.
5.The melting point of a substance is considered a characteristic property while the freezing point is not.