Vaporisation and Fusion

The thermal energy released or absorbed during a phase shift, without increasing or reducing the temperature of the thermodynamic system, is known as latent heat. There are various types of latent heat, each of which is determined by a substance’s transitions. The latent heat of fusion, evaporation, solidification, and condensation are examples of latent heat. To put it another way, these are the units of heat per mass needed to achieve the phase shift. The study of heat transmission and thermal effects is widespread in the discipline of thermodynamics.

The latent heat of fusion is the amount of heat energy necessary to transform a unit mass of a substance from solid to liquid at its melting point without changing its temperature. It’s indicated by ( Hf ).

Melting or fusing is the process of changing a substance from a solid to a liquid form by adding heat. The fusion point or melting point of a solid is the temperature at which it begins to melt. When a process is reversed, for example, when a liquid is cooled, it becomes a solid. The freezing point of a substance is the temperature at which it transitions from a liquid to a solid-state.

Melting points vary depending on the substance. A substance’s freezing point, on the other hand, is the same as its melting point.

It is denoted by Hf.

Hf = ΔQf/ m

or Δ Qf = m Hf

A substance’s latent heat of vaporisation is a physical attribute. It’s the amount of heat it takes to alter one mole of liquid at its boiling point under ordinary atmospheric pressure. It’s measured in kilograms per mol or kilogrammes per kilogramme of energy. When a liquid material is given energy, it transforms into a vapour; the energy absorbed in this process is known as heat of vaporisation. The heat of vaporisation of water is approximately 2,260 kJ/kg, or 40.8 kJ/mol. H v. is the symbol for it. J/kg is its SI unit. Its formula is as follows:

Qv/m = Hv

Fusion

The amount of heat required to melt the frozen liquid is known as the heat of fusion. It can be used to figure out how much a solution’s freezing point has dropped. The nature and strength of forces that hold the molecules of the solvent together in the solid or liquid form determine the magnitude of heat of fusion and heat of vaporisation. The stronger the intermolecular binding forces in a solid or liquid, the higher the value of heat of fusion or heat of vaporisation. When a solvent dissolves a solute, the heat of fusion is utilised to calculate the freezing point depression.

The enthalpy change of any amount of substance as it melts is known as the latent heat of fusion. The specific heat of fusion is the enthalpy change per amount of substance in moles when the heat of fusion is linked to a unit of mass, whereas the molar heat of fusion is the enthalpy change per amount of substance in moles.

The latent heat of fusion is almost always positive; the sole known exception is helium. At temperatures below 0.3 K, helium-3 exhibits a negative enthalpy of fusion. Below 0.77 K (272.380 °C), helium-4 has a slightly negative enthalpy of fusion.

Vaporisation

The highest known heat of vaporisation is that of water. The heat of vaporisation is the amount of heat required to transform 1 g of liquid into a vapour without raising the liquid’s temperature. The vaporisation heat is latent heat.

After a substance’s temperature has reached any of these points, latent heat is necessary to change the state of the substance from solid to liquid at its melting point, or from liquid to gas at its boiling point. It’s worth noting that latent heat isn’t linked to a change in temperature, but rather a change in condition. It’s vital to keep in mind that vaporisation is an endothermic process in which heat is extracted from the liquid by boiling. At the boiling point, a liquid’s temperature will remain constant until all of the liquid has evaporated. The heat of vaporisation is proportional to the strength of intermolecular forces; the higher the intermolecular forces, the higher the heat of vaporisation. The lower the vapour pressure, the stronger the intermolecular forces are. The point at when everything comes to a boil. The temperature at which a liquid’s vapour pressure equals the external pressure.

Conclusion

In the atmosphere, latent heat is quite essential. This is the factor that plays a role in the creation of convective clouds and, as a result, the atmosphere’s stability. When latent heat is absorbed or given away, it causes climate instability, potentially resulting in extreme weather. The heat required for an object to transition from a solid to a liquid form, or vice versa, is known as the latent heat of fusion. Because it has a significantly higher value than specific heat, it allows you to keep a beverage cold for much longer by adding ice to it rather than just having a chilly liquid, to begin with. A substance’s latent heat of vaporisation is a physical attribute. When a liquid material is given energy, it transforms into a vapour; the energy absorbed in this process is known as the heat of vaporisation.