Why water behaves differently from other liquids
As a leading manufacturer of adiabatic cooling equipment, we work with water day in, day out. Sometimes, in the absence of sufficient levels of glycol anti-freeze, we deal with ice too.
When the latter happens and the water in our coolers freezes, the coils in our heat exchangers split outwards, which seems odd given that liquids are denser the colder they become. Surely the mass should become smaller, not greater, don’t you think?
Recent scientific studies have revealed that water in fact bucks the trend for behaviour compared to other liquids, and here, I’ll explain a few key points to help you understand what happens to one of the world’s most precious resources at a molecular level.
Density
Typically speaking the density of a liquid increases the cooler it becomes, meaning it reaches its most dense at freezing point. This would mean that a frozen body of any liquid should sink in a bath of its liquid counterpart – so why do ice cubes float?
Water reaches its maximum density at a temperature of 4°C, before slowly decreasing in density below that level. Which means when it freezes at 0°C, it is in fact less dense than its liquid counterpart. This is why water ice floats and bodies of water freeze from the top down.
So, when an anomaly occurs in best practice cooler maintenance and a system doesn’t contain enough glycol anti-freeze during the colder months, the water in the system freezes and becomes larger in density, splitting the coils outwards, causing plant breakdown.
More distinct differences
Before we consider the molecular cause of water’s unusual behaviour, there are a number of other distinct differences to note, including:
- Water has a far higher surface tension compared to all other liquids, with the only exception being Mercury. This is what allows certain insects to skate across the top.
- Water has an unusually high boiling point compared to other liquids like most alcohols which have a boiling point of around 64°C and Ethanol which boils at 78.4°
- It dissolves many different chemical substances. In fact, it dissolves more chemicals than any other liquid known to man.
The answer lies in its molecular structure
Intrigued by its unusual behaviour, researchers from the University of Bristol and the University of Tokyo* closely examined the molecular structure of water and found that by altering its formation at a molecular level, they could make water behave more typically compared to other liquids.
Water has a tetrahedral molecular arrangement, which means every molecule is bonded to four others in a rough pyramid shape. Using a supercomputer and state-of-the-art computer modelling techniques, researchers have altered this pyramid arrangement to create various altered behaviours such as making frozen water denser than liquid water so that it sinks rather than floats – a characteristic far more typical of liquids like those mentioned above.
Now for the difficult bit. We know that the reason water behaves differently is due to the tetrahedral (pyramid) arrangement of its molecules. Four of these pyramids can in fact share a common water molecule at the centre without overlapping, and it is the presence of this particular, highly ordered water molecule, combined with other disordered arrangements, that gives water its peculiar properties.
Why is all this important?
The crux of the matter is, without water and its unusual behaviour, life as we know it would change. Here’s a few reasons why:
- Water doesn’t compress easily, which means it can be pushed for the generation of power, the use of hydraulics in industry and even for the transportation of blood cells in our bodies
- It’s an incredible solvent, carrying nutrients in plant and animal life
- It freezes from the top, meaning water-dwelling animals and plants can survive beneath the surface
- It has a very high specific heat capacity, this means a small amount of water can absorb a lot of energy. This makes it very good for taking large amounts of heat away from systems with only small volumes so that it can be easily reused or dissipated by our coolers. This also helps to maintain water temperature stability within systems and avoid spikes. g. it takes a massive 4.19kJ to raise 1kg of water by 1°K. In contrast, mineral oil only has a specific heat capacity of 1.67kJ/kg/K meaning the same amount of energy would cause 2.5 times the amount of temperature fluctuation
*This research has been published by PNAS, source link https://www.sciencealert.com/water-unique-properties-tetrahedral-molecule-arrangement
