Why does temperature remain constant during melting/boiling?

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Discussion Overview

The discussion revolves around the phenomenon of temperature remaining constant during the phase changes of melting and boiling. Participants explore the implications of temperature in systems involving ice and water, as well as the behavior of substances during distillation. The scope includes conceptual understanding and technical reasoning related to thermal equilibrium and phase transitions.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that during melting, energy is absorbed to break bonds, which keeps the temperature constant despite the addition of heat.
  • Others question whether an ice/water mixture can be considered to be at a single temperature, suggesting that the melted water could potentially heat up while the ice remains at 0°C.
  • One participant suggests that increasing pressure could raise the melting point, leading to further discussion about the relationship between temperature and phase changes.
  • There is a consideration of thermal equilibrium, with some participants arguing that small systems can be at a single temperature while larger systems may have temperature variations.
  • A later reply introduces the idea that in distillation, the temperature of the vapor can exceed the boiling point of the liquid, raising questions about the behavior of substances during phase changes.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the ice/water system is at a single temperature or if different parts can have different temperatures. The discussion remains unresolved with competing views on thermal equilibrium and the implications for phase changes.

Contextual Notes

Participants express uncertainty regarding the definitions of thermal equilibrium and the behavior of substances at different scales. The discussion highlights the complexity of phase transitions and the conditions under which temperature remains constant.

Who May Find This Useful

This discussion may be useful for individuals interested in thermodynamics, phase transitions, and the conceptual understanding of temperature in physical systems.

sgstudent
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When ice melts at 0°C, energy is being absorbed to break the bonds. And so temperature remains constant. However, when some of the atoms enter the liquid state why can't they continue gaining heat and increase in temperature. So that this way, the overall temperature increases instead of remaining the same?

Thanks in advance :)
 
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Let's start from the top. Do you think your ice/water mix is at a single temperature or not?
 
Vanadium 50 said:
Let's start from the top. Do you think your ice/water mix is at a single temperature or not?

I think so? Because in the graph for temperature against time it stays constant for the substance that's being heated during its melting.
 
OK, so if it is all at the same temperature, how do you bring the ice to above its melting point without melting it?
 
Vanadium 50 said:
OK, so if it is all at the same temperature, how do you bring the ice to above its melting point without melting it?

I think by increasing the pressure the melting point would increase. But even at normal atmospheric pressure, if we have a piece of ice that's is melting in a 25 degrees environment, won't the melted part of the ice/water be exposed to the 25 degrees environment and get heated up while the ice part would continue melting at 0°C?

So in other words in a 25°C room, the ice part of the ice/water part is still 0°C while the water part can be at a temperature greater than 0?
 
So are you arguing that the system is all at the same temperature (#3) or not (#5)?
 
Vanadium 50 said:
So are you arguing that the system is all at the same temperature (#3) or not (#5)?

Hmm I'm thinking when the ice is taken out to a hot environment, it starts to melt. So the ice part of the system is still 0 degrees while the water part that melted from the ice is free to heat up to above 0 degrees?
 
So now you have to decide whether you are talking about "small" things or "large" things. Small things are in thermal equilibrium, which means they have one temperature. Large things - like the Earth - are not in thermal equilibrium, and different parts can have different temperatures. Your confusion stems from trying to take a statement about small things and apply it to large things.
 
Vanadium 50 said:
So now you have to decide whether you are talking about "small" things or "large" things. Small things are in thermal equilibrium, which means they have one temperature. Large things - like the Earth - are not in thermal equilibrium, and different parts can have different temperatures. Your confusion stems from trying to take a statement about small things and apply it to large things.

Hi thanks for the reply

Would the ice/water vase be like the small thing that's in thermal equilibrium? because I was thinking about the distillation case also whereby the thermometer would read the temperature of the gas to be at the bolong point of the gas exactly. But similarly to this case, I thought the evaporated gas can actually heat up to be more than its boiling point. For example in a ethanol water fractional distillation the temperature read is 78degrees initially which is the boiling point of the ethanol. But as the ethanol vaporized I thought it could increase in temperature as well.

Thanks so much for the help
 

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