3 posts • Page 1 of 1
Ok so this might be hard to explain without the picture but basically while converting a liquid to a gas, by increasing the heat you don't actually change the temperature of the substance itself because all that extra heat is being used to hold the newly developing phase. Temperature of a substance only begins to increase after it reaches the gas phase because the last phase is already achieved and therefore that additional heat only increases the temperature. Lavelle asked us why water at 100 degrees C (boiling) causes less damage that steam (water vapor) also at 100 C. This is because while both have the same temperature, the steam has a greater enthalpy in order to hold its high form/phase. This means that when steam comes in contact with skin, it must release all of its extra enthalpy that makes it vapor in order to condense to 100C water, then it must also release energy until it is the temperature of the skin where as the water at 100C only releases enough energy to match the temperature of this skin. Thus, steam releases A LOT more energy and the water at the same temperature, meaning the steam is gonna hurt a lot more lol. Hope this makes sense
If you look at a heating curve for water, and you look at liquid at 100 degrees the water will drop from 100 to about 25 degrees when it touches the skin as about 5 kj of energy is released. When steam touches the skin, it is suddenly going form a gas to a liquid so much more energy or heat is being released (roughly 41 kj as mentioned in lecture) and that sinks into the skin. Since steam releases much more heat than water does when it touches the skin this causes a more severe burn. Also, the enthalpy for vaporization is large for water which also adds to the more severe burn.
Who is online
Users browsing this forum: No registered users and 2 guests