# What is Melting Point?

Image Credit:
3.bp.blogspot.com
Main Image:

The melting point of a solid is the temperature at which it changes from solid state to liquid state. At the melting point the solid and liquid phase exists in equilibrium (balance). The melting point of a substance depends (usually slightly) on pressure and is usually specified at standard atmospheric pressure. When considered as the temperature of the reverse change from liquid to solid, it is refereed to as the “Freezing point or crystallization point”. Due to the ability of some of the substances to super cool, the freezing point is not considered as the characteristic property of a substance. Super cooling a liquid is the process of cooling a liquid past its freezing point without it turning into a solid. When the “characteristic freezing point” of a substance is determined, the actual methodology is almost always “the principle of observing the disappearance rather than the formation of ice&amp;rdquo;, that is the “Melting Point”.

Content

### How to measure the Melting point?

Many laboratory methods exist for the determination of melting points.

• Kofler bench: A Kofler bench or Kofler hot-stage microscope is a metal strip with a temperature gradient (range room temperature to 300 degree centigrade). Any substance can be placed on a section of the strip revealing its thermal behavior at the temperature at that point.
• Thiele tube: Thiele tube is a laboratory glass ware designed to contain and heat an oil bath. A basic melting point apparatus for the analysis of crystalline solids consist of an oil bath with a transparent window and a simple magnifier. An oil bath is a laboratory heating device which uses boiling oil as the temperature regulator. The several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bathe is heated (and stirred) and with the help of the magnifier (and extent light source) melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, and optical detection is automated.

### How is Melting point discussed in terms of Thermodynamics?

From thermodynamics point of view, at the melting point the change in Gibbs free energy (?G) of the material is zero, but the enthalpy (H) and the entropy (S) of the material are increasing. Gibbs free energy also known as free enthalpy is a thermodynamic potential that measures the useful work obtainable from a thermodynamic system. Enthalpy is a measure of total energy of a thermodynamic system. Entropy is the measure of disorder of a thermodynamic system. Melting phenomenon happens when the Gibb’s free energy of the liquid becomes lower than the solid for that material. At various pressures, this happens at a specific temperature. It can be shown that

?S = ?H/T, where T, S and ?H are respectively temperature at the melting point, change in entropy of melting and the change in enthalpy of melting. Unlike boiling point, the melting point is relatively insensitive to moderate changes in pressure because the solid/liquid transition represents only a small change in volume.

### What is Carnelley's rule?

In organic chemistry, Carnelley’s rule established by Thomas Carnelley, stated that high molecular symmetry is associated with high melting point. Molecular symmetry is the symmetry (evenness) present in molecules and the classification of molecules according to their symmetry. A high melting point results from a high enthalpy of fusion, low entropy of fusion or both. In highly symmetrical molecules the crystal phase is densely packed with many efficient intermolecular interactions in a higher enthalpy change on melting.

### What is Lindemann's criterion on melting point?

An attempt to find out the bulk melting point of crystalline materials was first made by Fredrick Lindemann, an English physicist in 1910. The idea behind the theory was the observation that the average amplitude of thermal vibration increases with increasing temperature. Melting initiates when the amplitude of vibration becomes large enough for adjacent atoms to partly occupy the same space. The Lindemann criterion states that melting is expected when the root mean square vibration amplitude exceeds a threshold value. Assuming that all atoms in a crystal vibrate with the same frequency ‘v’, the melting point is estimated using the expression for the Lindemann criterion as given below:

Tm = 4 ?m vca2/kB, where

• m is the atomic mass,
• v is frequency of vibration of atoms in the crystal,
• c is the Lindemann constant,
• a is the atomic spacing,
• kB is the Boltzmann constant, and
• Tm is the absolute melting point temperature (in kelvin)

External References

Extraordinary Article it its truly useful and inventive update us as often as possible with new upgrades. its was truly important. much appreciated. http://prescottpapers.pen.io/

Great article, much obliged for assembling this! This is clearly one extraordinary post. A debt of gratitude is in order for the important data and bits of k
nowledge you have so given here. article source

A debt of gratitude is in order for sharing the data, keep doing awesome... I truly delighted in investigating your site. great asset... Zombie Lenses

This web journal site is really cool! How was it made ! search engine optimization company in oklahoma

A debt of gratitude is in order for the site stacked with such a variety of data. Halting by your website assisted me with getting what I was searching for. favicon converter png to ico

I am extremely cheerful to find your post as it will get to be on top in my accumulation of most loved websites to visit. make money online earn

Your site is truly cool and this is an incredible rousing article. buy peptides

I really thank you for the valuable info on this great subject and look forward to more great posts. Thanks a lot for enjoying this beauty article with me. I am appreciating it very much! Looking forward to another great article. Good luck to the author! All the best! scuba-diving-la-palma.de

Thanks for the blog loaded with so many information. Stopping by your blog helped me to get what I was looking for. rankworx.de

I truly inspired after read this on account of some quality work and educational musings . I just wanna express profound gratitude for the author and want you to enjoy all that life has to offer for coming!. Accounting

Much obliged to you for another extraordinary article. Where else would anyone be able to get that sort of data in such an impeccable method for composing? I have a presentation one week from now, and I am on the search for such data. Accounting

I can"t read articles online all the time, yet I"m happy I did today. This is exceptionally elegantly composed and your focuses are very much communicated. Kindly, absolutely never quit composing. vegetarian markets near me

I really like your blog. Great article. silver needle tea

Very interesting and different! Keep it coming! I love the way you write and share your niche! omegle alternatives

I have been looking at a couple of your stories and i can state really well done. I will bookmark your online journal marijuana laws by state map

I as of late discovered numerous helpful data in your site particularly this online journal page. Among the loads of remarks on your articles. Much obliged for sharing. The Tube Funnel Review

I usually dont commonly post on many another Blogs, nevertheless Thank you continue the astonishing work. Ok unfortunately its time to get to school. software development company

Wow what a Great Information about World Day its exceptionally pleasant educational post. a debt of gratitude is in order for the post. top 10 ways make money online

Thanks for a wonderful share. your article has prooved your hard work and experience you have get in this field.  Phonepe customer care number

After research a couple of of the blog posts on your web site now, and I truly like your approach of blogging. I bookmarked it to my bookmark web site listing and can be checking again soon. Pls check out my web page as well and let me know what you think. brushed nickel towel warmer

Super site! I am Loving it!! Will return once more, Im taking your food additionally, Thanks. sample research paper rationale

Truly an extraordinary expansion. I have perused this wonderful post. A debt of gratitude is in order for sharing data about it. I truly like that. Much obliged so part for your meet. how to create video blog

It’s how you can tell if a is actually working or otherwise. click here

Can I just now say what a relief to find one who in fact knows what theyre speaking about online. You definitely understand how to bring a problem to light making it essential. Workout . should see this and understand this side from the story. I cant think youre less well-known when you absolutely provide the gift. commercial real estate

Oh my goodness! a wonderful article dude. Thanks a ton Nonetheless I am experiencing trouble with ur rss . Don’t know why Unable to join it. Can there be anybody obtaining identical rss issue? Anybody who knows kindly respond. Thnkx bad review

This is such an extraordinary asset, to the point that you are giving and you give it away for nothing. I cherish seeing sites that comprehend the benefit of giving a quality asset to free. It is the old what circumvents comes around schedule. Every Door Direct Mail Printing

Thank you for the auspicious writeup. It in fact was a amusement account it. Look advanced to far added agreeable from you! By the way, how can we communicate? In Home Dog Training Service near Chelmsford MA

I might want to say this online journal truly persuaded me to do it! Much obliged, great post. Zwembaden