does blood heat up as airpressure drops? why?

Question

I was watching a documentary about space and atmosphere which claimed that if you didn't wear a space suit, your blood would heat up and eventually boil as you ascended due to the reduction in air pressure. Is this true and what is the physics behind it?

Answer 1

It doesn't heat up but it will have a tendency to evaporate and expand. Evetually, if the pessure drops low enough, it will boil. But not because it's hot, because of the vacuum. PV=nRT.

Answer 2

pV=RT, when this is applied to the scenario you gave, and other liquids as well, then the liquid will heat up and the boiling point is lowered. When p->0 (in a vacuum), for pV=RT if T remains constant then V would have to increase, this is not the case. I've seen a beaker of water put in a chamber that decreased in pressure. It wasn't good enough to get a perfect vacuum, but then again nothing is. After the experiment was conducted, the temperature of the water was higher than it's initial temperature. I felt the difference.

So to answer your question, your blood will heat up and eventually boil, but at a lower temperature. Either way you would be dead before you would feel those effects.

Answer 3

To maintain the equality of the equation PV=nRT, if the pressure drops and volume and number of mols remain constant, the the temperature would actually have to drop. however all liquids will boil when the liquids vapor pressure equals the environmental pressure. So at some point the blood would boil but you would probably be dead before that happened. If you have a medicine syringe that is about 10cc and you fill it with 3-4 cc of water, cap the end with you finger and pull back on the plunger, the water will boil at room temperature and you will see the bubbles form. Aint science neat?

Answer 4

Blood will heat up only if heat energy is added. In the space suit scenario, loss of pressure would not add heat energy. However there is a high school lab experiment where water is heated to boiling on a Bunsen burner then removed. The water can be made to boil again by placing the container under a partial vacuum (using lab equipment). The atmosphere (14.7 psi) prevents boiling unless the water temperature is 212F or greater. At lower pressures nothing prevents boiling at lower temperatures. In the vacuum of space there is zero pressure to prevent boiling of water (or the water in blood) regardless of its temperature. Warm blood will boil in space in an open container or within a human body that is not pressurized to prevent boiling.

Answer 5

My guess is you misheard. They probably said your blood would "boil," which does not necessarily mean your blood would heat up.

Liquids boil (off gas) at different temperatures, depending on the nature of the liquid and on the atmospheric pressure pushing in on the liquid. For a given liquid, water for example, boiling starts at lower and lower temperatures as the atmospheric pressure becomes lower and lower.

This is why, when camping in the mountains and trying to boil an egg, you have to leave that three minute egg boil for, maybe, four or five minutes to get the same degree of doneness. That water is boiling at something less than the 212 deg F that water boils at when at sea level where the atmospheric pressure is higher. For example, at 5,000 feet, water boils at 203 deg F according to the source below.

The same thing would be true of your blood. As you get into lower and lower atmospheric pressures, the temperature required to make it off gas nitrogen and other gases would get lower and lower. Finally, out in space with little or no pressure, you'd get to a point where ordinary body temperature would suffice to make your blood boil.

Answer 6

Blood doesn't heat up as the air pressure drops. No liquid does. Either the doumentary was inexcusibly wrong or you missed a bit.

All liquids, including blood, boil at lower temperatures when the ambient air pressure drops. This is because the energy needed for the molecules to evapourate decreases when the air pressure 'holding it in' is lessened.

Answer 7

As pressure drops, liquids don't get hotter but their boiling temperature drops. In fact, if you lower the pressure enough -- about 1/100 of an atmosphere -- you can get water that boils WHILE IT'S FREEZING. This is called the "triple point", and I have seen it happen myself in a plexiglass vacuum chamber at the Exploratorium in San Francisco.

Answer 8

PV over T is a constant and this is Boyle's law. This means that when your blood pressure goes up so does your blood temperature - hence the red faces of old colonels supping their Scotch