Thermodynamics: Open or Closed System

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Discussion Overview

The discussion revolves around the concepts of open and closed thermodynamic systems, specifically focusing on the behavior of water in a sealed container as it undergoes phase changes due to heating. Participants explore the implications of evaporation and condensation, the nature of energy transfer, and the conditions under which equilibrium might be reached.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants describe the process of water evaporating in a closed system and question whether the condensation of water vapor on the walls represents an exothermic reaction.
  • There is a discussion about whether the rate of evaporation and condensation will reach equilibrium and how the presence of a heat source affects this process.
  • One participant suggests that if the walls of the container were perfect insulators, all water could eventually evaporate, but acknowledges that in reality, heat loss would prevent this.
  • Another participant raises the idea that the change of phase involves energy transfer but questions the implications of losing "stuff" in a closed system.
  • There is a mention of entropy and its role in thermodynamic processes, with some participants arguing about the nature of entropy changes in different systems.
  • One participant emphasizes the utility of water vapor compared to liquid water, suggesting that steam has greater potential for work in thermodynamic applications.
  • Questions arise regarding the relationship between the amount of water and air in the container and how it affects evaporation rates, with a focus on the size of the container.

Areas of Agreement / Disagreement

Participants express differing views on the implications of phase changes, energy transfer, and the concept of losing "stuff" in a closed system. The discussion remains unresolved, with multiple competing perspectives on these topics.

Contextual Notes

Some participants reference concepts such as quantum physics and entropy without fully integrating them into the main discussion, indicating potential gaps in the assumptions or definitions being used. The discussion also touches on the practicalities of thermodynamic systems without reaching a consensus on specific outcomes.

Who May Find This Useful

This discussion may be of interest to students of chemistry and physics, particularly those exploring thermodynamics, phase changes, and energy transfer in closed and open systems.

AndjpANDJ
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Ok this is solely for my interest. I should know this if I were taking Grade 12 Chemistry, but I haven't had this course in two years, and neither have I continued in pure science since then so please if you know better tell me if this is correct AND if it is only so because the case is of a closed system:

You are cooking water, but the water is in a pot that is in a sealed box (without pores, but the lid is closed, like pretend it is a clear plastic box).

The water starts to evaporate because it is undergoing an endothermic reaction from the cooking fire (but the air becomes hotter because it is a closed system and has no where to escape to).

The air becomes saturated with water vapour and this starts to condense on the walls. Since it's condensing; does this mean that it is suddenly an exothermic reaction? Provided that the heat source continues; will this water continue evaporating and condensing back? Which reaction will happen quicker, or will it eventually do so at a constant rate becomes it ends up in equilibrium?

Now; we take away the heat source. I guess it'll end up turning back into liquid, until it condenses just enough for a natural rate of evaporation and condensation (like when you close a waterbottle cap).
 
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AndjpANDJ said:
Ok this is solely for my interest. I should know this if I were taking Grade 12 Chemistry, but I haven't had this course in two years, and neither have I continued in pure science since then so please if you know better tell me if this is correct AND if it is only so because the case is of a closed system:

You are cooking water, but the water is in a pot that is in a sealed box (without pores, but the lid is closed, like pretend it is a clear plastic box).

The water starts to evaporate because it is undergoing an endothermic reaction from the cooking fire (but the air becomes hotter because it is a closed system and has no where to escape to).

The air becomes saturated with water vapour and this starts to condense on the walls. Since it's condensing; does this mean that it is suddenly an exothermic reaction? Provided that the heat source continues; will this water continue evaporating and condensing back? Which reaction will happen quicker, or will it eventually do so at a constant rate becomes it ends up in equilibrium?

Now; we take away the heat source. I guess it'll end up turning back into liquid, until it condenses just enough for a natural rate of evaporation and condensation (like when you close a waterbottle cap).
Closed and open depend on if you want stuff to go to boundary or not.

I can have a lot of STUFF go on in a closed boundary system, but I can also have a little stuff go on inside a system but a lot of stuff HAPPEN because the boundary isn't closed.
 
The air becomes saturated with water vapour and this starts to condense on the walls. Since it's condensing; does this mean that it is suddenly an exothermic reaction? Provided that the heat source continues; will this water continue evaporating and condensing back? Which reaction will happen quicker, or will it eventually do so at a constant rate becomes it ends up in equilibrium?

The water vapor touches the walls which are still cool enough to absorb heat from the vapor, causing it to condense. Over time if you kept the heat up and had the correct mix of water and air, you could get all of the water to turn into vapor and no longer condense on the walls since they will heat up and eventually reach equalibrium with the rest of the box.(Assuming the walls were perfect insulators and didn't transfer heat to the outside. But in reality this isn't the case) In a real experiment the walls would continually give off heat, and unless your heat source provided enough heat you might not ever reach the point where all the water is evaporated.
 
By the change of phase you have lost a whole lot of stuff.

What can we define, what can we measure, what can I contemplate?
 
mt8891 said:
By the change of phase you have lost a whole lot of stuff.

What can we define, what can we measure, what can I contemplate?

What do you mean? The change of phase is simply losing or gaining energy. If it is a sealed box that doesn't let anything in or out, then we havn't lost any matter.
 
You've lost stuff. If you can't observe it you can't observe it...after that we move into quantum physics. What happens to water inside of an infinitely long pipe of radius R? I dunno, the pipe is infinite. We can make measurements and say "at such and such point the quality will be such and such" but that is only because of what we know.

Entropy, converting stuff into junk, tends toward the maximum. If there is no entropy generated, we still have entropy change unless the system is isentropic. We have rules for that though. We need to know what sort of cycle we are dealing with. We need to know some of the states it is going through. From that we can determine what we need. We can figure out how it behaves.

http://www.spiraxsarco.com/resources/steam-tables.asp

Look at it this way. I can do a lot more with water VAPOR than I can do with LIQUID water. Liquid Water is cool but it's just a liquid. It has liquid properties. It does what liquid does. I want steam. Why? Because I can make steam do a lot of stuff that water can but better. Steam can propel a turbine BUT it can do it with awesomeness. Liquid water can do it but it sucks at it. It's quality is zero.

Equilibrium depends upon the dead state conditions. If the water is left there after it boils and just sits eventually it will go to whatever state those conditions say it should go to. On the contrary, the environment will say "Hey, there is some crazy water here" and adjust itself so that it goes to the lowest state it can so that it doesn't violate those RULES we know about. However, it does not do anything funny. It simply does what the water is doing. It goes to a dead state, it tries to go toward an equilibrium. These are just heat reservoirs trying to go to the dead state.
 
Last edited:
mt8891 said:
You've lost stuff. If you can't observe it you can't observe it...after that we move into quantum physics. What happens to water inside of an infinitely long pipe of radius R? I dunno, the pipe is infinite. We can make measurements and say "at such and such point the quality will be such and such" but that is only because of what we know.

Entropy, converting stuff into junk, tends toward the maximum. If there is no entropy generated, we still have entropy change unless the system is isentropic. We have rules for that though. We need to know what sort of cycle we are dealing with. We need to know some of the states it is going through. From that we can determine what we need. We can figure out how it behaves.

http://www.spiraxsarco.com/resources/steam-tables.asp

I have no idea what any of that has to do with the original post. His question was easily answered without going into detail about quantum physics and entropy.
 
Whoops.
 
Drakkith said:
... if you kept the heat up and had the correct mix of water and air...

Thanks everyone for their responses. For yours Drakkith, by correct mix of water and air do you mean relative to the container? Or both proportionally to themselves in relation to the container? (because I feel as if the amount to evaporate would change to a lot more if the container were larger)


...do you have some degree that involves Chemistry to know this? Or is it common knowledge if you're hypothesizing, although you sound highly credible.
 
  • #10
AndjpANDJ said:
Thanks everyone for their responses. For yours Drakkith, by correct mix of water and air do you mean relative to the container? Or both proportionally to themselves in relation to the container? (because I feel as if the amount to evaporate would change to a lot more if the container were larger)


...do you have some degree that involves Chemistry to know this? Or is it common knowledge if you're hypothesizing, although you sound highly credible.

Whatever proportion of water to air in your container that would result in all of it being able to evaporate. I don't know what that would be.

No degree, just using my acquired knowledge. It's entirely possible that I'm incorrect, but I don't think so.
 
  • #11
Cool, Thanks!
 

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