At What Temperature Does CO2 Freeze?

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CO2, or carbon dioxide, will freeze at -78 degrees Celsius at normal pressure. Find out how a change in pressure can change the freezing point of carbon dioxide with help from a science teacher and field biologist in this free video on chemistry.

Part of the Video Series: Chemistry & Biology
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Video Transcript

Hi, I'm Brian with Today we're going to discuss at what temperatures CO2 freezes. So CO2 or carbon dioxide is a fairly abundant compound and you're probably fairly familiar with its solid form, dry ice. Now carbon dioxide sort of had this interesting phenomena that happens. It goes through sublimation which is the process of turning directly from a solid to a gas. So in order to really answer the question of at what temperature carbon dioxide freezes, we need, that depends based on what our pressure is. So we're going to look at a phase diagram which shows when carbon dioxide is a solid, a liquid and a gas. So here we have a phase diagram of CO2. On your Y axis you have pressure and atmospheres. And on the X axis you have temperature in degrees Celsius. Now I apologize, but I was not able to draw this diagram to scale. So you'll have to just bear with me here. I have the important numbers marked. So the first thing you'll notice, well we live at one atmosphere. That's the normal pressure that you find here on earth. So one atmosphere is going to be our reference point. So to answer the question, at what temperature it freezes, CO2 freezes, we have to look at this line that divides it. Anything on the left side of the line, CO2 is going to be a solid. So at one atmosphere we're right here. I'll put a, I'll erase part of our line. And you'll notice that handily, I've written a temperature right below it. So, CO2 becomes a solid at negative seventy eight degrees Celsius. That's pretty darned cold. I think if I can do my conversion right, that's negative a hundred and eight point five degrees Fahrenheit. So, that's negative a hundred and eight degrees Fahrenheit. If you were to increase the pressure though. Say maybe the five atmospheres, you'll notice that we don't need quite as much temperature to make it freeze anymore and right here, CO2 at five atmospheres, CO2 will freeze at negative fifty seven degrees Celsius. So a dramatic change. You won't see CO2 in a liquid form unless you increase the pressure even more and your temperature is much warmer. So at normal atmosphere though we see CO2 going directly from solid to gas. So, in a brief summary, carbon dioxide at normal pressures will freeze at negative seventy eight degrees Celsius. This has been a brief discussion of the freezing point of CO2.


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