Heating curve for water
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Heating curve for water
Can someone explain again the heating curve for water, and how water vapor at 100 C causes a more severe burn than 100 C liquid water?
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Re: Heating curve for water
During the heating curve as the professor showed in class, there are flat lines where energy is still being given to the reaction, but no temperature change is occurring. This is due to the energy needed to change the phase at 0º from Ice to Water and at 100º from water to steam/gas.
Re: Heating curve for water
The reason why steam at 100ºC causes more severe burns than liquid water at 100ºC is because of the enthalpy of vaporization.
We know that it takes a relatively large amount of energy to boil liquid water into steam. Therefore, we can assume that condensing steam into liquid water will release a relatively large amount of energy.
So when 100ºC steam makes contact with the skin, it will condense, releasing this energy onto the skin. This is unlike 100ºC water, which will just decrease in temperature.
Hope this helps!
We know that it takes a relatively large amount of energy to boil liquid water into steam. Therefore, we can assume that condensing steam into liquid water will release a relatively large amount of energy.
So when 100ºC steam makes contact with the skin, it will condense, releasing this energy onto the skin. This is unlike 100ºC water, which will just decrease in temperature.
Hope this helps!
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Re: Heating curve for water
Even though the liquid water and water vapor (steam) are at the same temperature, because so much energy is required for the phase change from water to vapor, the steam contains a lot more energy than than the liquid water does. When the steam and liquid water come in contact with skin, they both give off their heat until the skin and water are the same, but the vapor has a lot more water to give off, so it causes a more serious burn than liquid water at the same temperature.
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Re: Heating curve for water
If you look at the heating curve for water, you'll notice that the third flat line that marks the transition from liquid to water vapor is pretty long compared to the others. This flat line indicates that the substance requires more heat (energy) to change phases. The temperature will not change because all of that energy is devoted to changing water from liquid to gas instead of actually heating the substance. As a result, steam at 100 degrees Celsius will have absorbed more energy than liquid water at 100 degrees Celsius, and will result in a more severe burn if touched.
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Re: Heating curve for water
In the heating curve of water, the temperature increases with an input of heat when the phase is the same, but when the phase is changing, temperature is not changing since the energy is used to break the bonds between molecules. So, the same quantity of hot water and steam means that the steam will have more energy. When the steam hits your skin, a lot more energy will be released compared to the amount of energy released by contact with hot water because the steam has to release the energy to undergo the phase change from vapor to liquid and then release more energy to get to that equilibrium temperature.
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Re: Heating curve for water
The heating curve for water shows how much energy is absorbed by water as the temperature increases and changes state. As the water absorbs energy, it increases in temperature. When the water reaches the temperature for a phase change (0 °C/100 °C), it continues to absorb energy but no longer changes temperature until the entire quantity of water has changed phase. Once all the water is in the same phase, the temperature continues to rise. Steam would cause a more sever burn than water of the same temperature because it would release energy while changing phase while the water would not as it does not change phase when cooling to body temperature.
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Re: Heating curve for water
When heat is added, temperature normally increase. However, during phase change (e.g. when liquid is changing into vapor), heat is absorbed but temperature remains constant. So, 100 degree celsius of steam holds much more heat than 100 degree celsius of liquid water. Therefore, more heat is transferred to our hands when we touch steam compared to liquid water.
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Re: Heating curve for water
Just a few general comments about the hearting curve for water. The curve itself shows how the temperature of a given quantity of water changes as heat is added at a constant rate. During a phase change, the temperature of the water remains constant, resulting in the plateau on the graph. The slopes we see is the release or intake of energy depending on which way your transition is traveling.
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Re: Heating curve for water
because the water vapor needs to release more energy as it changes phase from gas to a liquid
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Re: Heating curve for water
Adding onto what everyone else said, if you look at the heating curve for water, when vapor cools on your skin, it releases 40.7 KJ/mol of energy as it is changing phases from a vapor to a liquid. After it releases all of this energy, it still is at 100 degrees Celsius when it is in condensation form which is very hot compared to just scalding boiling water starting at 100 degrees Celsius. This is a lot more energy and heat compared to just a hot water burn.
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