WEBVTT

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This is Giancoli Answers
with Mr. Dychko.

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So, this ice cube is gonna get dropped
into an insulated container

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containing liquid nitrogen.

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And we assume that all the energy
gained by the liquid nitrogen

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just goes into changing its phase
from liquid into gas.

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And we assume
that the gaseous nitrogen

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is not affected by the ice cube.

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And so there's no
temperature change happening there.

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And that makes sense
because the ice cube will be

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submerged within the liquid nitrogen,

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and the gas will be,
you know, above that.

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So, it won't be in contact
with the ice cube.

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So, this is the amount
of heat energy gained

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by the liquid nitrogen
in order to change phase

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from liquid to gas.

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And this is the energy lost
by the ice cube

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as it changes its temperature.

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And we can isolate mass
of nitrogen that'll vaporize

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by dividing both sides by <i>L</i>,

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and switch the sides around.

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And so the mass of nitrogen
is going to be the mass of the ice

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which is 0.028 kilograms

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multiplied by the specific heat of ice

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which is 2,100 joules
per kilogram Celsius degree

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times the initial temperature
of the ice minus its final temperature.

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And that's 273 degrees kelvin
minus 77 kelvin.

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I guess you don't normally
say degrees kelvin, you say kelvin.

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But, you know, it's a small point.

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And also it's not really good
to say <i>Δt</i> there either

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because this is,

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you know, when you have a <i>Δ</i> there,
it's usually final minus initial,

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but in this case its initial temperature
of the ice minus its final temperature.

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OK.

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So, when we divide all that

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by the latent heat
of vaporization for nitrogen,

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200 times 10
to the 3 joules per kilogram.

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And that's 0.058 kilograms of nitrogen

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will change phase from liquid into gas.