(a) When you exercise vigorously, you sweat. How does this...

Name: Problem 83, Chapter 11: Chemistry The Central Science
Uploaded: 2020-04-16T13:50:37-08:00
Duration: 4 min 18 s
Channel: Jennifer Landry
Description: (a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

Key Concepts

Latent Heat of Vaporization

Latent heat of vaporization is the amount of energy required for a liquid to change into a gas without a temperature increase. This energy absorption during the phase change leads to cooling of the remaining liquid, which can eventually cause it to freeze if enough heat is removed.

Evaporative Cooling

This is a process in which a liquid, as it turns into gas, absorbs heat from its surroundings. In the context of sweating, the evaporation of sweat from the body absorbs heat, which helps cool the body during vigorous exercise.

Boiling Point and Pressure Relationship

The boiling point of a liquid depends on the external pressure applied. When pressure is lowered, as with a vacuum pump, the boiling point decreases, causing water to boil at temperatures lower than expected.

Transcript

00:01 All right, question 83 is a qualitative question.

00:04 The first part says, a, when you exercise vigorously, you sweat.

00:09 How does this help cool your body? so we're looking at the relationship between sweating, or a, we're looking at the relationship between sweating and the cooling of your body.

00:27 So when you sweat, the sweat starts as a liquid, and it vaporizes to a gas.

00:35 Gas, right? the sweat starts to evaporate off of you.

00:39 And in doing so, this process of going from a liquid to a gas is an endothermic process, meaning it requires energy, it requires heat to break those intramolecular forces that hold the sweat, which is a mixture of water and salts and proteins and other components.

00:58 In order to break all those intramical forces and separate them out as a gas that requires energy.

01:06 And the liquid is going to want to evaporate because it's trying to hit the vapor pressure.

01:12 But assuming you're not sweating in a closed box, you're not going to hit vapor pressure equal to atmospheric pressure because you're in the atmosphere.

01:20 You're continuously, the gases are continuously going off and therefore not in an enclosed container.

01:26 You're going to continue to sweat and sweat.

01:28 And you're going to continue, this is going to continue to change into a, a gas and vaporize and vaporize because you're not, again, in a closed container where the vapor pressure can build up to atmospheric pressure.

01:39 So it's going to continue to vaporize continuously.

01:42 And that process is an endothermic process.

01:45 And where is it getting the heat from? it's getting the heat from an energy for this endothermic process.

01:50 It's getting it from your body.

01:52 So it's taking energy or heat from your body to change your sweat from a liquid to a gas, thus cooling your body because it's removing the heat.

02:03 So that is why sweating is a cooling process.

02:07 Part b says a flask of water is connected to a vacuum pump.

02:11 A few moments after the pump is turned on, the water begins to boil.

02:15 After a few minutes, the water begins to freeze...

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