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What Is Latent Heat: A Layman’s Guide to Its Critical Concepts

Latent heat is described as the amount of energy that is absorbed or released, for a substance to change its state. (Technical term is phase change). For example, the additional heat required for turning water into water vapor, or on the contrary, the heat released, when vice versa happens. (Water vapor > water, because of condensation).

When the phase change is ongoing (not yet 100% complete), a couple of things are going on:

  1. The temperature of the substance remains the same.
  2. Once the entire phase change cycle is finished, at that point, the temperate starts to change. For instance, when you’re boiling a pot of water, the temperature of the water would remain the same, until all of the water is boiled.
  3. The extra energy that’s needed or released to change state, is precisely what latent heat is. Think of it as a hidden form of energy that you can’t see, but know is there. To understand this better, follow along to learn why water steam burns more.

Why Steam Burns More Than Water

Why Steam Burns More Than Water
Demonstration: Steam being released from a kettle.

To understand this concept, remember this:

  • There is always more energy when a phase change is transpiring than a temperature change.
  • For example, making the water warmer, in theory (all things being the same), will need less energy than actually changing into a water vapor/steam. When liquid [water], converts into gas [steam], a phase change occurs.

With that in mind, when steam touches the skin of your hand, the following happens:

  1. The steam starts turning into a liquid form (phase change).
  2. And because a phase change occurs, extra energy is released. Therefore, your hands feel that, than a simple temperature change.

Types of Latent Heat

Principally, there are two types of latent heat.

  1. Latent Heat of Fusion: This is typically associated with the energy required to convert a solid into a liquid — such as that tied to melting ice into water.
  2. Latent Heat of Vaporization: Similarly, this is usually connected to the energy needed to convert a liquid into a gaseous state — like that related to transforming water into water vapor.

With those two laid out, there is also a third common one, which is referred to as the “latent heat of sublimation.” Sublimation is a unique case where a solid can directly change to a gaseous state (skipping the liquid form).

And therefore, its latent heat can be defined as the necessary energy used for a sublimation phase change — as in dry ice, or solid air fresheners used in restrooms that directly change into a gaseous form.

Other FAQs

How Is Sensible Heat Different From Latent Heat?

Sensible heat is the amount of energy utilized to change temperature, up or down (not phase). In other words, the heat needed to raise or decline the temperature of a substance/object. When there are conversations about sensible heat, it’s mostly referring to the literal temperature numbers (excluding latent heat).

What Is Latent Heat of Condensation?

Akin to the already covered 3 types, latent heat of condensation refers to the quantity of energy released when water vapor turns into tiny droplets (or a similar event with any other substance; gas to liquid). This is literally, the opposite of the latent heat of vaporization.

Can You Measure Latent Heat With a Thermometer?

In most cases, no, you cannot. Additionally, the thermostats in your home, also likely do not measure the latent heat. What I mean by that is: Sometimes, you can see that your thermostat is telling you it’s 70 degrees Fahrenheit; however, you may feel that it’s more like 80 degrees Fahrenheit. You’re not wrong in feeling that way because the supplementary 10 degrees is likely felt due to the presence of latent heat/humidity (which contains latent heat).

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Conclusion

From boiling water to turning on air conditions and the resulting temperature readings from it, latent heat is a naturally occurring phenomenon that is experienced in our everyday lives. On a much broader scale, our understanding of this concept plays a significant role in weather studies and whatnot.

Hopefully, with this post, you’re clearer on what it is, and when next time you experience such an occurrence, you can connect the dots.

Other Interesting Resources

  1. Latent Heat Calculator
  2. More reading on sensible heat, latent heat, and HVAC.