WEBVTT - How does dry ice work?

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<v Speaker 1>now exclusively on iTunes. Hi Am Marshall Brain with today's question,

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<v Speaker 1>how does dry ice work? Dry ice is frozen carbon dioxide.

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<v Speaker 1>A block of dry ice has a surface temperature of

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<v Speaker 1>minus a hundred nine degrees fahrenheit or minus seventy eight

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<v Speaker 1>degrees centigrade. Dry ice also has the very nice feature

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<v Speaker 1>of sublimation. As it breaks down, it turns directly into

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<v Speaker 1>carbon dioxide gas, rather than ever becoming a liquid. The

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<v Speaker 1>super cold temperature and the sublimation feature make dry ice

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<v Speaker 1>great for refrigeration. For example, if you want to send

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<v Speaker 1>something frozen across the country, you can pack it in

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<v Speaker 1>dry ice. It'll be frozen when it reaches its destination

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<v Speaker 1>and there won't be any messy liquid leftover like you

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<v Speaker 1>would have with normal ice. Many people are familiar with

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<v Speaker 1>liquid nitrogen, which boils at minus three hundred and twenty

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<v Speaker 1>degrees fahrenheit. Liquid nitrogen is fairly messy and difficult to handle.

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<v Speaker 1>So why is nitrogen a liquid while carbon dioxide is

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<v Speaker 1>a solid. This difference is caused by the solid liquid

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<v Speaker 1>gas features of nitrogen and carbon dioxide. We're all familiar

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<v Speaker 1>with the solid liquid gas behavior of water. We know

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<v Speaker 1>that at sea level, water freezes at thirty two degrees

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<v Speaker 1>fahrenheit and boils at two hundred twelve degrees fahrenheit. Water

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<v Speaker 1>behaves differently as you change the pressure. However, as you

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<v Speaker 1>lower the pressure, the boiling point falls. If you lower

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<v Speaker 1>the pressure enough, water will actually boil at room temperature.

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<v Speaker 1>If you plot out the solid liquid gas behavior of

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<v Speaker 1>a substance like water on a graph showing both temperature

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<v Speaker 1>and pressure, you create what's called a phase diagram for

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<v Speaker 1>the substance. The phase diagram shows the temperatures and pressures

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<v Speaker 1>at which a substance changes between a solid, a liquid,

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<v Speaker 1>and a gas. When you look at the phase diagram

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<v Speaker 1>for carbon dioxide, what you can see is that at

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<v Speaker 1>normal pressures, carbon dioxide moves straight between a gas and

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<v Speaker 1>a solid. It's only at much higher pressures that you

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<v Speaker 1>find liquid carbon dioxide. For example, a high pressure tank

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<v Speaker 1>of carbon dioxide or a carbon dioxide fire extinguisher contains

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<v Speaker 1>liquid carbon dioxide. To make dry ice, you start with

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<v Speaker 1>a high pressure container full of liquid carbon dioxide. When

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<v Speaker 1>you release the liquid carbon dioxide from the tank, the

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<v Speaker 1>expansion of the liquid and the high speed of operation

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<v Speaker 1>of carbon dioxide cools the remainder of the liquid down

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<v Speaker 1>to the freezing point, where it turns directly into a solid.

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<v Speaker 1>If you've ever seen a carbon dioxide fire extinguisher inaction,

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<v Speaker 1>you've seen this carbon dioxide snow form in the nozzle.

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<v Speaker 1>You compress the carbon dioxide snow to create a block

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<v Speaker 1>of dry ice. Do you have any ideas or suggestions

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