Why Does Alcohol Not Freeze Easily?

The molecules of alcohol have weak intermolecular force between them. This lack of strong H-bonding makes it difficult to freeze alcohol.

Have you ever wondered why a bottle of pure ethanol doesn’t freeze, even when you store it in the deep freezer? As you may know, alcohols are characteristically difficult to freeze into their solid states, as these organic molecules tend to stay in their liquid state. The solidification of different liquids depends on several factors.

But why do liquids solidify in the first place? And what conditions lead to it?

Since ethanol is the most common alcohol, this article will primarily focus on this type. The terms ethanol and alcohol will be used interchangeably in this article.


Recommended Video for you:

If you wish to buy/license this video, please write to us at admin@scienceabc.com.

Why Do Liquids Freeze?

Freezing can be simply defined as a compound transforming from its liquid to its solid state, but what causes liquids to undergo this process?

Every compound has some internal energy that is dependent on the temperature around it. This internal energy controls the state in which the substance exists. When the temperature around the compound reduces, the internal energy available to the compound reduces as well. This leads to an increase in the intermolecular forces.  

Ice cubes

Freezing of water occurs at 0°C (Photo Credit : George Hodan / Public Domain Pictures) 

When heat is removed, the molecules of the compound come closer together. This is why many liquids begin to solidify at a low temperature. However, different liquids have different freezing points. 

The freezing point of a liquid is the temperature at which that liquid transitions into a solid state. Water has a freezing point of 0° Centigrade, but ethanol has a freezing point of -114° Centigrade. This means that to freeze alcohol, you have to drop its temperature below -100° C! 

The huge difference in the freezing point of the two liquids is due to the huge difference between their intermolecular forces. The molecules of water are bound more tightly to each other than the molecules of ethanol.

Intermolecular Forces and Hydrogen Bonds

Intermolecular forces help bind the molecules to each other so they do not separate. Gases have the lowest amount of intermolecular force, whereas solids have the highest. The explanation for this is rather simple. The intermolecular forces between molecules in the liquid state are less than those in a solid state, but more than in gases.

These forces are dependent on the distance of the molecules from each other. The distance is the highest in gases, and lowest in solids. Intermolecular forces are also dependent on the nature of the molecules. Hence, some molecules inherently have greater intermolecular forces.

The most important bond displaying strong intermolecular force is something called H-bonding. The hydrogen atom of one water molecule forms an intermolecular H-bond with the oxygen atom of another molecule. Sometimes, hydrogen atoms make stronger bonds, depending on the atom to which they are connected.

Hydrogen Bonds in Water and Ethanol: A Comparison

For example, let’s take a look at the structure of water:

Water Molecule Ball and Stick

Water molecule showing one central oxygen atom bound to two hydrogen atoms (Photo Credit : MsKDinh/ Wikimedia Commons)

Here, you can see one oxygen atom bound to two hydrogen atoms. Now, these two hydrogen atoms must bind to the oxygen of another molecule, which gives rise to a structure like this:

Hydrogen Bonds Between Water Molecules

Figure Depicting Covalent Bonds and Hydrogen Bonds between Water Molecules (Photo Credit : OpenStax College/ Wikimedia Commons)

Now, let’s see what an ethanol molecule looks like:

Ethanol-structure.svg

Ethanol structure showing two central carbon atoms bound to five hydrogen atoms and one alcohol (-OH) group (Photo Credit : Lukáš Mižoch/Wikimedia commons)

An ethanol molecule has two carbon atoms attached to each other. Each carbon atom can make three more bonds. The first carbon has three hydrogens, while the second has two hydrogens and one alcohol (-OH) group attached. It is this -OH group that forms the hydrogen bonds between alcohol molecules.

Hydrogen bonds

Figure depicting Hydrogen Bond between two ethanol molecules

However, since the oxygen is connected to a carbon, the polarity of the oxygen goes down. Polarity here is the amount of negative or positive charge that an atom possesses in a neutral molecule.

The more polar the atoms in a molecule, the more polar the molecule becomes. Here, water is much more polar than ethanol, which is why the H-bonds in water are so much stronger.

How Does This Affect Freezing?

Coming back to our initial question: why is ethanol hard to freeze? We know that alcohols have very little polarity, or are non-polar. The intermolecular forces between individual ethanol molecules are very low.

Since those intermolecular forces are low, the molecules tend to stay away from each other. Until the molecules come together, the compound cannot exist in a solid state.

The ethanol molecules do not come together on their own. Extremely low temperatures are needed to solidify the compound. Simply put, the lack of attraction between the molecules makes it difficult for alcohol to freeze.

Conclusion

As compared to liquids like water, it is much more difficult to freeze alcohol. Even in the -15 °C of a common home freezer, a bottle of pure ethanol will refuse to solidify.

This is because ethanol is an organic, non-polar compound and cannot make strong hydrogen bonds. This affects the intermolecular forces and makes them weak. Since the H-bonds and intermolecular forces are weak, the ethanol molecules refuse to cooperate and join together.

This leads to the compound having higher energy, so it needs a much lower temperature to solidify. This is why it is so difficult to freeze alcohol!

Suggested Reading

Was this article helpful?
YesNo
Help us make this article better
Scientific discovery can be unexpected and full of chance surprises. Take your own here and learn something new and perhaps surprising!

Follow ScienceABC on Social Media:

About the Author

Arushi holds a graduate degree in Biomedical Sciences from the University of Delhi. Ever since she was a kid, Arushi has loved books and reading has been an escapist experience for her. It was only natural that her love for books further manifested itself as a flair for writing and poetry. However, her one true love in life is Biology and she can never tire of the marvel that is the human body. When not studying or working, you can find her writing poetry, going on runs and watching the sunset!

.
Science ABC YouTube Videos

  1. Neutron Stars Explained in Simple Words for LaymenNeutron Stars Explained in Simple Words for Laymen
  2. How Robert J. Oppenheimer became the ‘Father of the Atomic Bomb’How Robert J. Oppenheimer became the ‘Father of the Atomic Bomb’
  3. Higgs Boson (The God Particle) and Higgs Field Explained in Simple WordsHiggs Boson (The God Particle) and Higgs Field Explained in Simple Words
  4. Slowing or Reversing Aging: Can We Live for 180 years?Slowing or Reversing Aging: Can We Live for 180 years?
  5. Detectives Use this Simple Technique to Find Your Fingerprints (Even AFTER You Have Wiped Them Off)!Detectives Use this Simple Technique to Find Your Fingerprints (Even AFTER You Have Wiped Them Off)!
  6. Why is a Circle 360 Degrees, Why Not a Simpler Number, like 100?Why is a Circle 360 Degrees, Why Not a Simpler Number, like 100?
  7. Quantum Mechanics Explained in Ridiculously Simple WordsQuantum Mechanics Explained in Ridiculously Simple Words
  8. Do Fish Get Thirsty and Do They Need to Drink Water?Do Fish Get Thirsty and Do They Need to Drink Water?