• Skip to primary navigation
  • Skip to main content
  • Skip to footer
Zippy Facts Logo

Zippy Facts

Interesting Random Facts

  • Animals
  • Culture
  • Firsts
  • Food
  • Geography
  • Health
  • History
  • Inventions
  • Language
  • Mythology
  • Odds
  • People
  • Religion
  • Science
  • Space
  • Universe
  • World
You are here: Home / Science / What is the Difference Between the Freezing Point and Melting Point of a Substance?

What is the Difference Between the Freezing Point and Melting Point of a Substance?

May 11, 2020 by Karen Hill

The melting point and the freezing point of a substance are the same thing.

The solidification process is what we also call freezing. When we say that water freezes at 32 degrees Fahrenheit (0 degrees Celsius), we could just as well say that that’s the melting point of ice. The reason they are the same is that the slithering molecules of a liquid must be slowed down to a certain definite energy in order for them to fall into their permanent, rigid places in a solid crystal; on the other hand, they must be heated up to that same amount of energy in order to break free from those rigid positions and begin to flow as a liquid.

A calorie is not a Calorie. A calorie is an amount of energy. While energy can exist in a variety of interchangeable forms, the most familiar form to most people is heat. So a calorie is generally regarded as an amount of heat.

But precisely how much heat? Ask a chemist and you’ll get one answer, but ask a dietitian or nutritionist and you’ll get another. And they’re not even close; one “calorie” is a thousand times bigger than the other. It’s as if one person’s kilometer were another person’s meter; in order to interpret a highway sign, you’d have to know who wrote it.

There’s no indication that the chemists and nutritionists will ever agree; they’re both too set in their ways. So the world is stuck with two sizes of calories.

The chemist’s calorie, which we might call a gram calorie, is the amount of heat it takes to raise the temperature of one gram of water (about 20 drops) by one degree Celsius. But that’s a pretty small amount of energy, so the nutritionist uses the food calorie: the amount of heat it takes to raise the temperature of a thousand grams of water by one degree Celsius. Thus, one food calorie is equal to a thousand gram calories.

To avoid confusion, I’ll use calorie with a lower-case c for the gram calorie and Calorie with a capital C for the food calorie. So when you see it written both ways, they’re not typos. Anyway, you can pretty much tell which one is meant by its context.

Thus, a certain definite amount of heat is involved in the melting-freezing transition of any substance between its solid and liquid forms. For pure water, that amount of heat happens to be eighty calories per gram. If you want to melt a gram of ice, you’ve got to put eighty calories of heat into it; if you want to freeze a gram of liquid water, you’ve got to take eighty calories of heat out of it.

Just to be contrary, chemists do not call that amount of heat the “heat of melting” or the “heat of freezing.” They call it the “heat of fusion.”

To make things even worse, whenever a substance happens to be a liquid at room temperature and we have to cool it to make it a solid, people call the transition temperature a freezing point, whereas if the substance is a solid at room temperature and we have to heat it to convert it to a liquid, people call that very same transition temperature a melting point.

Go fight City Hall.

Related Facts

  • Why does the freezing point of water change with pressure and why doesn't deep sea water freeze?
  • Why does Adding Salt to Ice and Water Make it So Much Colder Than the Freezing Point?
  • How Do You Change the Freezing Point of Fresh Water?
  • What Would a Surfboard Have To Be Made of To Be Able To Surf Down Molten Lava Flow Without Melting?
  • How do skating rinks keep the ice on the rink from melting?
  • What Does the Term "Moot Point" Mean and Where Did the Phrase For an Irrelevant Point Come From?

Filed Under: Science

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

Previous Post: « Why does Sugar Melt But Salt Doesn’t?
Next Post: How Do Microwaves Cook Food From the Inside Out? »

Footer

Follow

  • Facebook
  • Flickr
  • GitHub
  • Google+
  • Instagram
  • LinkedIn
  • Medium
  • Pinterest
  • StumbleUpon
  • Tumblr
  • Twitter
  • YouTube

Categories

Accomplishments Animals Culture Firsts Food Geography Health History Inventions Language Mythology Odds People Religion Science Space Universe World Your Body

About

Zippy Facts empowers the world by serving educational content that is accessible to everyone.

A tribute to growing up, zippyfacts.com showcases interesting and unusual facts about the world.

Our mission is to use technology to facilitate knowledge transfer and sharing.

Copyright © 2021 Zippy Facts

  • About Us
  • Contact
  • Privacy Policy