Enthalpy

[gwenkelley3L]

Hey can someone elaborate on what Lavelle was saying at the end of today's lecture, about how the enthalpy of vaporization is higher and that relates to it causing more severe burns? thanks!

[Austin_Schwartz_1L]

Hello,
While the temperatures of water and vapor may be roughly the same (~100 degrees C), the vapor contains much more heat energy. If you look at the chart giving during this portion of the lecture, you will see that vapor, when coming into contact with skin, must go through 40.7+5 kJ of energy, vs water which only releases the 5kJ. Because of this, burns from vapor are much more severe than burns from water.
I hope this helps!

[Gabrielle Malte 2G]

Yes! Since the breaking of bonds between molecules of a liquid to form a gas (vaporization) release more energy in the form of heat than those just being heated as a liquid, steam burns will be more severe than those caused by liquid.

[Kaitlyn Bateman 1L]

Hi!
Additonally, even after the vapor has transferred the energy from its condensation, it still transfers even more energy as it cools as a liquid (like what the energy of the water burn would transfer).

[Reagan Feldman 1D]

When water vapor reaches the skin, it must first condense to liquid form before changing temperature. This releases more heat onto the skin (higher enthalpy), thus a more severe burn.

[Kayla Arellano 1K]

Hey can someone elaborate on what Lavelle was saying at the end of today's lecture, about how the enthalpy of vaporization is higher and that relates to it causing more severe burns? thanks!

By looking at the heating curve for water, we can see that the change in enthalpy is much higher for vapors than liquid. This means that the vapor will release a lot more heat when it touches the skin compared to liquid.

[Mara Crooks 1F]

It seems like from his graph, what helped me think about it best was that vapor releases more energy as heat than liquid would so essentially it is just hotter and would burn more severely than liquid. That is how I interpreted it.

[Arjan G 2H]

Hi! So, the enthalpy of vaporization is much more dangerous than the enthalpy of fusion because of how much heat is needed for the phase change to occur. Using the example in the lecture, when boiling water is cooling down, it is releasing heat that it previously absorbed to allow it to start boiling in the first place. This means that the water is vaporizing less, and it is losing the energy it absorbed, which is about 6.01kJ per mole. Typically, this is not too intense of the head, and the vapor released is not too harmful to the human body. But, when steam is being phase changed back to a liquid, it releases much more energy into its surroundings, specifically about 40.7 kJ per mole. As you can see, this amount of heat is much higher than the heat released when water is cooling down after being boiled. This is because the steam possesses the heat from its enthalpy of vaporization as well as the heat that comes from the boiling water. Therefore, it releases more heat into its surroundings and can cause burns because of its high enthalpy of vaporization. I hope this helps!

[Alex FreeWolf 2E]

Hi,

Vapors have a significantly higher enthalpy than liquid. When vapors come into contact with the skin, they change from a gaseous state to a liquid state and therefore release energy. Boiling liquid water releases a certain amount of energy too. This means vapor not only releases the amount of energy that liquid water does but it also releases a substantial amount of energy due to its phase change (gas --> liquid, exothermic).

Hope this helps!