Steam vs. Water

[Isis_DW_3G]

Can someone re-explain why a high Enthalpy of Vaporization allows steam to cause more severe burns than water? I was confused by that. Thank you!

[KatarinaReid_3H]

High enthalpy of vaporization means that it takes a lot energy to make liquid water into gas. Therefore, when your skin makes contact with steam, it will cool the steam down enough to condense back into liquid water onto your skin. In order for the steam to change phases back into water, it has to release all that heat that originally allowed it to enter the gas phase (the enthalpy of vaporization). This heat is released onto your skin causing severe burns. The greater the enthalpy of vaporization, the more heat is absorbed when entering the gas phase and the more heat is released when leaving the gas phase to become water.

[Audra Mcleod 3G]

Hello!
When steam comes into contact with skin, the temperature difference between the two (with the skin being much lower in temperature) causes the steam to condense. In order to do so, the steam must release an amount of heat that corresponds to the enthalpy of vaporization, as this will enable it to enter the less energetic liquid phase. Since the heat of enthalpy is so high, this would result in roughly 40.7 kj/mol of heat being released (in addition to heat lost in the new liquid form) by the steam in this process, which would severely burn someone's skin.

[shevanti_kumar_1E]

Even though steam and water are the same temperature, steam can cause more severe burns because of the large enthalpy of vaporization. When steam burns your skin, it goes through a phase change. Going from a vapor to liquid is exothermic and releases energy, so when steam touches skin it drops in temperature and the energy is transferred into the skin which causes it to become a liquid.

The heating curve I attached also helped me understand and visualize this concept. Hope this helps!

[Andy Hon 3E]

Since steam coming in contact with the skin will turn into a liquid, the reaction will release a high amount of energy in the form of heat. The higher the enthalpy of vaporization is, the more energy a gas has, and thus more energy to be released.

[Madeline Louie 1B]

When steam comes in contact with your skin, the lower temperature of the skin causes the steam to condense into water. This phase change from steam to water causes a release in energy (heat) because this phase change is an exothermic reaction. Adding to this, the exothermic reaction means there is a large -enthalpy required to go from a gas phase to a liquid phase. (or a large + enthalpy to go from a liquid phase to a gas phase). hope that helps!

[Yeprem]

So basically the temperature does not change during the phase change but after the liquid is completely switched to vapor and more heat is still added then the temperature changes?

[Olivia Smith 2E]

So basically the temperature does not change during the phase change but after the liquid is completely switched to vapor and more heat is still added then the temperature changes?

Yes that is correct! All of the energy is going into breaking the hydrogen bonds to transform into a gas. But once the bonds are broken then the temperature will rise!

[Lucy_Balish_3G]

So basically the temperature does not change during the phase change but after the liquid is completely switched to vapor and more heat is still added then the temperature changes?

You can see this by looking at the slope of the heating curve graph. During phase changes, the slope of the graph is flat so the temperature does not change. But once all the bonds are broken then the heat goes into heating the substance as seen by the increasing slope and value of temperature on the graph.

[Pierce Newman 1A]

the reason why steam causes the more severe burns is due to the fact that steam has already gone through the phase change from liquid to vapor, and absorbed all that energy(shown on x-axis of heating curve). Boiling water that is at 100 degrees has not absorbed the energy required to change phases. Therefore, when steam comes in contact with 25 degree celsius skin, it has to release all that energy it absorbed in the phase change to cool back down to 25 degree water. the 100 degree water must cool down as well, but will not release nearly as much energy because it hasn't absorbed it while changing phases. The energy absorbed during the phase change is absorbed by the H-bonds holding water as a liquid, but does not change the temperature of the H2O. that way, both the water and steam can be at the same temperature but due to the phase difference they carry and release different amounts of energy.