To melt or not to melt ?

[doG]

Reversibility is not needed to show that melting has taken place .

Can you give us any example of any material where reversibility does not maintain the same composition you started with before you melted it?

[John Cuthber]

John Cuthber ,

 

The definition of melting is the topic in the thread , the thread began with the discussion of the definition of melting in mind , that was it's desired theme , it can't therefore degenerate .

Then the answer to your original question is "yes for some definitions of melt, but no for other definitions".

Which is, as far as I can see, pointless.

[Hal.]

CaptainPanic ,

 

I'm not going to tell you the inner workings of Poly(2-Vinylpyridine) , on quickly gathering a first insight about it I have noted that some people say they can melt a substance with this name above 200 degrees Celsius and others say a substance with this name decomposes at a temperature which they didn't say . As they surely have better equipment than I will ever have , I find their conclusions interesting especially when the said material is an ingredient in medical implants .

 

That doesn't prevent me from observing that to the best of my knowledge , which means I don't think it is untruthful that , when I see that an ice cube is solid and it goes from being solid at -5 degrees Celsius to being liquid at 5 degrees Celsius , part of what I am observing is melting , if you believe it has not melted , say so . If you should rely upon even one instance of melting which does not have reversibility as it's proof , then you will be relying on a definition I talk of .

 

doG ,

 

I don't think so , I don't think I did say so and if anybody would like to say they did I'm sure that will be interesting . Isn't it implied in the term reversibility that you wouldn't get a different composition , if you did that wouldn't be reversibility .

 

 

John Cuthber ,

 

As I thought John , if you want to make the circumstances fit the rules , make the rules fit the circumstances .

[CaptainPanic]

Hal,

 

Please read this wikipedia text which is the ultimate destruction of your point:

 

The enthalpy of fusion, also known as the heat of fusion or specific melting heat, is the change in enthalpy resulting from the addition or removal of heat from 1 mole of a substance to change its state from a solid to a liquid (melting) or the reverse processes of freezing. It is also called the latent heat of fusion, and the temperature at which it occurs is called the melting point. (source)

Note that it clearly says that the amount of energy needed going both ways (adding energy or removing it) is the same.

Also note that this piece of text is the 1st paragraph of the particular wiki-article (the part of the article where they give definitions).

 

And the fact that the energy is the same going both ways is what we call "reversibility". So, it's not just me saying melting / freezing is always reversible. You're up against Wikipedia too.

 

So, the status:

People and things say that melting freezing is reversible: Wikipedia, all experts on this forum, the entire scientific world.

People who still disagree: Hal.

 

Join us, it's much nicer to be right.

Edited August 10, 2011 by CaptainPanic

[Hal.]

CaptainPanic ,

 

You're problem with what you say is that you seem to think that I am arguing that melting is not reversible . This is not the case and if you think I do you really should say where it is that I say melting is not reversible , which you won't find because I didn't say that . I can only state it again , that melting is independent of reversibility and need not rely on reversibility for it's proof . If you disagree , say so . You're trying to tell me I'm wrong about something I don't ascert and I'm trying to tell you I'm speaking of something else .

 

 

For clarity , Hal. contends , melting is independent of reversibility and need not rely on reversibility for it's proof .

 

For clarity , do you agree CaptainPanic ?

[CaptainPanic]

You're problem with what you say is that you seem to think that I am arguing that melting is not reversible . This is not the case and if you think I do you really should say where it is that I say melting is not reversible , which you won't find because I didn't say that .

In fact, you say it in the very next sentence:

I can only state it again , that melting is independent of reversibility and need not rely on reversibility for it's proof .

When melting is by definition a reversible process, how can it be independent on it?

[Hal.]

CaptainPanic ,

 

For clarity , Melting is independent of reversibility and need not rely on reversibility for it's proof .

 

CaptainPanic , Do you agree ?

[CaptainPanic]

CaptainPanic ,

 

For clarity , Melting is independent of reversibility and need not rely on reversibility for it's proof .

 

CaptainPanic , Do you agree ?

I don't understand you.

When melting is by definition a reversible process, how can it be independent on it? I just don't understand your line of thinking.

 

p.s. I noticed that you speak Dutch, you can PM me if you think you can explain it better in Dutch (I live in the Netherlands).

We've come to a point now where we just repeat previous posts... this needs to end soon.

[Hal.]

Nearly ............................................ The End !

 

Let's for instance take the property of Mass . The Mass of an ice cube could be taken before and after two phase changes and if they are the same then there is Conservation of Mass . Any definition based on this Mass would be dependent on the Reversibility of Mass . If a definition was only based on the Mass before and after the first phase change this definition would not then be dependent on the Reversibility of Mass due to two phase changes , it would be Independent of the Reversibility of Mass .

Edited August 10, 2011 by Hal.

[John Cuthber]

This

"For clarity , Melting is independent of reversibility and need not rely on reversibility for it's proof ."

is an assertion made without any proof.

It is at odds with the usual meaning of the word "melting".

[Hal.]

The question is John Cuthber ,

 

In it's unusual meaning do you agree ?

[John Cuthber]

If you choose to define "melting " as turning into a pink bird and flying away then you are welcome to do so.

I just don't see the point of redefining words to mean something other than their normal meaning.

[Hal.]

John Cuthber , acknowledged , nitty gritty , do you agree ?

 

It is much more natural to observe that when a piece of ice is frozen and when it melts there is no reverse process of freezing to see before concluding the ice has melted . Billions of people do this every time they see something melting with no presumed reference to the reversible action .

 

It is much more natural to observe that when you see a solid piece of steel and afterwards put 200 amps through it to make it melt into a drop which falls into a puddle that it is melted with no presumed reference to the reversible action .

 

 

You could call me a Halite , an addition to the current possible meanings of Halite , which I would call a person who has this view .

 

Are you a Halite John ?

Edited August 10, 2011 by Hal.

[doG]

From Eric Weisstein's World of Physics

 

Melting

The phase transition of a solid to a liquid. The opposite is freezing.

 

This definition implies reversibility Hal. Would you contend it is in error?

[Hal.]

 

Melting

 

 

The phase transition of a solid to a liquid. The opposite is freezing.

 

This definition implies reversibility Hal. Would you contend it is in error?

 

 

 

I could contend it is in error and I could also contend it isn't in error , like a debate where one person is given one side and another another of an argument . I can be quite clear what I think this means without having to contend one or other side of a debate though .

 

The definition is termed , ' Melting ' . It is a phase transition of a solid to a liquid . The opposite phase transition is termed , ' Freezing ' . They are reverse processes .

[John Cuthber]

"It is much more natural to observe that when a piece of ice is frozen and when it melts there is no reverse process of freezing to see before concluding the ice has melted ."

Or, equally,

It is much more natural to observe that when a puddle of water is liquid and when it freezes there is no reverse process of melting to see before concluding the water has frozen.

 

"Natural" just depends on where you start from.

 

I would only be inclined to call you a halite if you were a chlorite or bromite.

[Hal.]

John Cuthber ,

 

My view is clear on melting and on fusion . A ' Halite ' would agree with the views of ' Hal ' just like a ' Brownite ' would agree with the views of a man named ' Brown ' and a ' Johnsonite ' would agree with the views of a man named ' Johnson ' . Any dictionary will include words that have multiple meanings and the term ' Halite ' is already one such word . If you agreed with me we could then conclude the equality of being a ' Cuthberite ' and a ' Halite ' in some instances .