We explain what the melting point is. what are its characteristics and some examples. Also, what is the boiling point.
What is the melting point?
The melting point is called the degree of temperature in which the matter in solid state it melts, that is, it passes to liquid state. This occurs at a constant temperature and is an intensive property of the matter, which means that it does not depend on your mass or its size. The melting point is the temperature at which a solid turns into a liquid and during this transition the solid and the liquid coexist.
The pure substances have higher melting points and with a lesser degree of variation than impure substances (mixtures). The more mixed the matter is, the lower its melting point (which, in addition, will have a greater variation). Therefore, the mixtures have a lower melting point than their pure components. On the other hand, solid mixtures have what is known as the "eutectic point", that is, the minimum temperature at which this type of mixture melts. The more mixed the matter is, in general, its melting point will be lower, until it reaches the eutectic point. With this in mind, the relationship between these properties can be used to determine the degree of purity of some materials.
The melting point is also less affected by the Pressure than the boiling point, and is usually equal to the freezing point of matter (at which liquids become solids) for most substances.
In some cases the melting point will have negative values: this means that from that temperature a frozen substance will return to its initial liquid phase.
Fusion, therefore, is a process change phase (solid to liquid) that operates from the introduction of caloric energy to the system or to the substance, making the atoms move with greater speed, increasing the collisions between them, breaking the structure rigid and therefore flow.
It is a very common process in the metallurgical industry, for example, where minerals and metals are fused to give them a specific shape before allowing them to regain their solidity upon cooling and losing the heat supplied.
Melting point examples
Some examples of melting points are as follows:
- Melting point of Water solid (ice) (H2O): 0 ºC
- Melting point of copper (Cu): 1085 ºC
- Melting point of aluminum (Al): 660 ºC
- Melting point of gold (Au): 1064 ºC
- Melting point of silver (Ag): 962 ºC
- Melting point of steel: around 1375 ºC (depending on its alloy)
- Carbon melting point (C): 3500 ºC
- Potassium melting point (K): 64 ºC
- Tungsten melting point (W): 3422 ºC
- Melting point of argon (Ar): -189 ºC
- Melting point of alcohol: -117 ºC
- Melting point of iron (Fe): 1539 ºC
- Melting point of lead (Pb): 328 ºC
- Mercury melting point (Hg): -39 ºC
- Nitrogen melting point (N): -210 ºC
- Hydrogen melting point (H): -259 ºC
- Melting point of acetaldehyde: -123.5 ºC
Boiling point
The boiling process is what happens when water boils and transforms it into steam.
The boiling point is the temperature at which the vapor pressure of a liquid (pressure that vapor exerts on the liquid in a closed system at a certain temperature) is equal to the pressure around the liquid. When both pressures are equal, the liquid turns into gas. The pressure of the environment has a great influence on the boiling point, that is, if a very high pressure is applied to a liquid, it will have a higher boiling point than if it is subjected to lower pressures and, therefore, it will take more to transform into steam when subjected to high pressure. So, since the boiling point varies greatly at different pressures, the IUPAC defined the standard boiling point: the temperature at which a liquid turns into vapor at the pressure of 1bar.
When we increase the temperature of a liquid above its boiling point but continue to supply heat to continue raising the temperature, we reach a temperature called "critical temperature." At temperatures above the critical temperature, it is impossible to liquefy a gas by increasing its pressure.
Melting point and boiling point are not comparable and should not be confused.