The heat of evaporation is the latent heat required by a substance to go from a liquid to a gaseous state.
If we focus on the field of physics, heat is the energy that is transferred from one body to another, capable of generating a change of state and the dilation of these bodies. Latent , on the other hand, is that which is hidden or seems inactive.
The notion of latent heat refers to heat that, when received by a body, does not increase its temperature , but is used to produce a change of state .
It is important to highlight that temperature is the physical magnitude that is responsible for expressing the level of heat. In the case of latent heat, therefore, it is energy that does not increase that magnitude in the body.
What is latent heat
It can be said that latent heat is the energy that a body or substance requires to change its state . A substance in a liquid state, for example, needs a certain latent heat to pass into a gaseous phase. In this context latent heat can be called heat of evaporation . In a similar sense, a solid substance requires latent heat to transition to a liquid state: the heat of fusion .
Since the heat does not translate into a variation in temperature while the change of state takes place, it appears to be hidden . That is why we speak of latent heat, since heat is added to the substance without changing its temperature.
Latent heat is the energy needed to achieve a change of state.
Historical tour
The use of this concept to describe the phenomenon observed when a body or substance changes state without the applied heat affecting its temperature derives from a remote time in which scientists believed that heat was a fluid substance, and They called caloric .
This responds to a model called caloric theory , which served for a long time to explain the behaviors and physical features of heat, understanding it as a fluid, which was said to permeate matter and be the cause of its heat.
Latent heat and sensible heat
When heat is applied to a substance that does not register a change of state but its temperature does increase, experts refer to sensible heat . It is worth mentioning that this is the way in which we understand heat in everyday speech, since we only consider the variation in temperature.
With respect to sensible heat, most of the experiments carried out indicate that to affect the temperature of a given body we need to apply an amount of heat directly proportional to its mass and the delta of temperatures that we intend to reach.
The example of melting ice
To continue with the explanation of the concept of latent heat, let us take, for example, an experiment through which we apply heat to an ice cube; Given that the latter is at a temperature below 0 °C, where the water had to change from liquid to solid state in the first place for us to obtain the piece of ice, we will have to reach that threshold and cross it if we want to see the reverse process. .
From the moment we reach 0 °C and until the ice cube has completely melted , its temperature will not change. The reason for this interruption in the increase in heat is due to the principle stated in the first paragraphs: latent heat is not used to affect the temperature of the body, but to produce its fusion.
As expected, once the piece of ice has melted, the temperature of the water will begin to rise until reaching the next point of change of state, which in this case is 100 °C, where the temperature will again remain stable. until all the substance evaporates .