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Why exactly is evaporation an endothermic process?
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+ Chemical reactions
+ Evaporation
+ Water
+ Chemistry
Posted by
Abid Hasan Rafi
Why exactly is evaporation an endothermic process?
The other answers, so far, are essentially saying “It’s endothermic because it’s endothermic.”
Your question is asking WHY is it endothermic.
Let’s talk about water and air, for simplicity. Water molecules are continually bouncing off of each other, and the average kinetic energy is the temperature, but individual water molecules from moment to moment have a distribution of kinetic energies, continually changing, with some fast, some slow, and most somewhere in between.
Sometimes a water molecule right on the boundary between water and air will get bumped by its neighbors from below in a combination that gives in a much higher kinetic energy away from the surface. Water molecules naturally attract each other, but that molecule might have enough energy to break free!
But most of the time it doesn’t. It gets pulled back.
But even more rarely, a water molecule has enough energy to actually break free and evaporate!
So why is this endothermic? The body of water below lost one of its most energetic water molecules, so its average kinetic energy has of course decreased. It’s cooler than it was.
And that escaping water molecule JUST BARELY escaped. So many water molecules ALMOST escape, and the ones that DO escape just barely make it. The high kinetic energy that allowed them to escape is lost because the attraction to the other water molecules, which almost prevented them from escaping, left them moving very slow. Thus the water vapor molecules are fairly cold as they become part of the air.
The water is colder, the air is colder, so it is endothermic.
The other answers, so far, are essentially saying “It’s endothermic because it’s endothermic.”
Your question is asking WHY is it endothermic.
Let’s talk about water and air, for simplicity. Water molecules are continually bouncing off of each other, and the average kinetic energy is the temperature, but individual water molecules from moment to moment have a distribution of kinetic energies, continually changing, with some fast, some slow, and most somewhere in between.
Sometimes a water molecule right on the boundary between water and air will get bumped by its neighbors from below in a combination that gives in a much higher kinetic energy away from the surface. Water molecules naturally attract each other, but that molecule might have enough energy to break free!
But most of the time it doesn’t. It gets pulled back.
But even more rarely, a water molecule has enough energy to actually break free and evaporate!
So why is this endothermic? The body of water below lost one of its most energetic water molecules, so its average kinetic energy has of course decreased. It’s cooler than it was.
And that escaping water molecule JUST BARELY escaped. So many water molecules ALMOST escape, and the ones that DO escape just barely make it. The high kinetic energy that allowed them to escape is lost because the attraction to the other water molecules, which almost prevented them from escaping, left them moving very slow. Thus the water vapor molecules are fairly cold as they become part of the air.
The water is colder, the air is colder, so it is endothermic.
The other answers, so far, are essentially saying “It’s endothermic because it’s endothermic.”
Your question is asking WHY is it endothermic.
Let’s talk about water and air, for simplicity. Water molecules are continually bouncing off of each other, and the average kinetic energy is the temperature, but individual water molecules from moment to moment have a distribution of kinetic energies, continually changing, with some fast, some slow, and most somewhere in between.
Sometimes a water molecule right on the boundary between water and air will get bumped by its neighbors from below in a combination that gives in a much higher kinetic energy away from the surface. Water molecules naturally attract each other, but that molecule might have enough energy to break free!
But most of the time it doesn’t. It gets pulled back.
But even more rarely, a water molecule has enough energy to actually break free and evaporate!
So why is this endothermic? The body of water below lost one of its most energetic water molecules, so its average kinetic energy has of course decreased. It’s cooler than it was.
And that escaping water molecule JUST BARELY escaped. So many water molecules ALMOST escape, and the ones that DO escape just barely make it. The high kinetic energy that allowed them to escape is lost because the attraction to the other water molecules, which almost prevented them from escaping, left them moving very slow. Thus the water vapor molecules are fairly cold as they become part of the air.
The water is colder, the air is colder, so it is endothermic.
Karl
The other answers, so far, are essentially saying “It’s endothermic because it’s endothermic.”
Your question is asking WHY is it endothermic.
Let’s talk about water and air, for simplicity. Water molecules are continually bouncing off of each other, and the average kinetic energy is the temperature, but individual water molecules from moment to moment have a distribution of kinetic energies, continually changing, with some fast, some slow, and most somewhere in between.
Sometimes a water molecule right on the boundary between water and air will get bumped by its neighbors from below in a combination that gives in a much higher kinetic energy away from the surface. Water molecules naturally attract each other, but that molecule might have enough energy to break free!
But most of the time it doesn’t. It gets pulled back.
But even more rarely, a water molecule has enough energy to actually break free and evaporate!
So why is this endothermic? The body of water below lost one of its most energetic water molecules, so its average kinetic energy has of course decreased. It’s cooler than it was.
And that escaping water molecule JUST BARELY escaped. So many water molecules ALMOST escape, and the ones that DO escape just barely make it. The high kinetic energy that allowed them to escape is lost because the attraction to the other water molecules, which almost prevented them from escaping, left them moving very slow. Thus the water vapor molecules are fairly cold as they become part of the air.
The water is colder, the air is colder, so it is endothermic.
Karl
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