phase change from liquid to vapor

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ursulavictorino1K
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Joined: Sun Feb 17, 2019 12:15 am

phase change from liquid to vapor

Postby ursulavictorino1K » Thu Jan 30, 2020 9:41 pm

I still don't understand why steam burns are so strong. Why does it matter that it takes more kJ/mol to change the phase from liquid to gas?

Justin Seok 2A
Posts: 104
Joined: Sat Aug 24, 2019 12:15 am

Re: phase change from liquid to vapor

Postby Justin Seok 2A » Thu Jan 30, 2020 9:50 pm

The steam and water can have the same temperature but the steam would carry more energy in the form of heat since it takes energy to drive a phase change from liquid to gas. Assuming that a burn would be stronger based on the energy it transfers onto skin, the steam would have a stronger burn.

Matthew Chan 1B
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Joined: Sat Sep 07, 2019 12:16 am

Re: phase change from liquid to vapor

Postby Matthew Chan 1B » Sun Feb 02, 2020 3:41 pm

If you look at the heating curve of water, there is a much bigger "flat line" going from liquid to vapor than from solid to liquid, which basically tells us that there is more energy required to vaporize. With this higher amount of energy required to vaporize compared to transition from solid to liquid, there is a lot more energy that is being released when steam burns you, which is why the burn is stronger.

Nikki Razal 1L
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Re: phase change from liquid to vapor

Postby Nikki Razal 1L » Sun Feb 02, 2020 3:54 pm

^^ the longer line going from liquid to vapor indicates that more heat was released, making the steam burn more than liquid water

TimVintsDis4L
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Re: phase change from liquid to vapor

Postby TimVintsDis4L » Sun Feb 02, 2020 4:11 pm

The process of steaming converting back into water as it touches your skin releases a lot of heat as a result of the phase change. That transition emits heat which can be seen as heat on top of the pre-existing 100 degrees.

Emily Lo 1J
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Joined: Thu Sep 19, 2019 12:16 am

Re: phase change from liquid to vapor

Postby Emily Lo 1J » Sun Feb 02, 2020 4:34 pm

It makes more energy to change from liquid water to water vapor. And as Matthew said, there is a longer flat line from liquid to vapor than from solid to liquid, which basically means that more energy is required to get to that vapor temperature.

Louise Lin 2B
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Re: phase change from liquid to vapor

Postby Louise Lin 2B » Sun Feb 02, 2020 4:51 pm

The more kJ/mol that the phase change takes, the more energy is released. A liquid burn does not have a phase change; it is merely the water that gets heated, but has not reached the point where enough energy changes the liquid into a gas. By contrast, a steam burn, upon contact with your skin, turns back into liquid, thereby releasing all the energy it initially had to change into a gas and a heated liquid. All that energy that gets released burns skin much more badly than a liquid burn.

William Francis 2E
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Joined: Wed Sep 18, 2019 12:20 am

Re: phase change from liquid to vapor

Postby William Francis 2E » Sun Feb 02, 2020 5:30 pm

Water molecules in steam have more energy at 100 degrees Celsius than the molecules in liquid water at the same temperature for the reason you stated. Even though the temperatures are the same, the steam contains more energy capable of doing work to mess up your skin upon contact.

Emily Burghart 1k
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Joined: Wed Sep 18, 2019 12:17 am

Re: phase change from liquid to vapor

Postby Emily Burghart 1k » Sun Feb 02, 2020 7:48 pm

Visible on the heating curve that we looked at in class, there is a significant amount of energy stored in vaporized water. When this vapor comes into contact with human skin (which is significantly cooler than the vapor) the vapor releases vast amounts of energy to return to its liquid state, which is in fact still extremely hot. Then the liquid water must also cool which gives off another significant amount of energy. The amount of energy released is far greater from its vapor state to its cooled liquid state than simply from its vapor state to its heated liquid state.


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