Why does adding water to boiling oil cause an explosion but nothing happens when adding oil to boiling water?
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Water can only reach as high as 100C before it starts boiling. No matter how much you heat up water at 100C, it wont get to 101C unless it is steam. Heating water more when its at 100C just makes it boil at 100C faster. Dump some oil in 100C water, and the oil will quickly rise to 100C but remain as a liquid.
Cooking oil can get to 212C before boiling. Dump some water into boiling 212C oil and and the water will quickly rise to 100C and start boiling extremely fast. Any liquid water also sinks in the boiling oil so that it is surrounded by super hot oil, making it boil even faster. It boils so quickly it causes dropplets of boiling oil to eject upwards and aerosolize, which has the potential to ignite into a fiery explosion.
It’s about why it explodes.
Water sinks in oil
Hot oil (like you’d see in a deep fryer) can get around 400°c before anything happens
Water when water gets to so much as 100°c, it becomes vapour.
When you put water into hot oil, the water sinks to the bottom, immediately gets boiled into water vapour, and the pressure of the water vapour is suddenly under a lot of pressure. *Boom*
When you put room temp oil in boiling water… The oil just floats on top. Since the water can’t get above 100°c, the oil can’t get remotely close to turning into a gas.
Oil begins to boil at approximtely ~300 degrees Celsius.
Water boils at ~100 degrees Celsius.
When you pour liquid water into boiling oil. The water is more dense and sinks to the bottom of the pot. The water absorbs heat from the oil and very quickly reaches its boiling point. The liquid water changes state (to a gas) at a rapid rate. A process that has a massive change in volume (~1000% change in volume).
Because of the rate and energy of this reaction the oil and liquid water are both are expelled out of the pot because of the expanding gases.
Now you have 300 degrees celcius oil all over the kitchen and it will ignite anything that will ignite at 300 degrees. .
As well, the ignition temperature of the oil is ~330 degrees c. So if your spilt oil contacts the cooking element you now have combustion. Which quickly ignites more oil in a chain reaction.
3 things combine:
1. Oil is much hotter than the boiling point of water
2. Water is denser than oil
3. Water expands something like 2700 times when it boils.
So you have water sinking in the oil, boiling as it sinks and expanding 2700 times.
Adding oil to boiling water just raises the temperature of the oil a little bit. It can sit above the boiling water just fine.
Its because the oil is much hotter, generally around 350°F for your avergae frier. The boiling point for water is 212°F.
Because water is heavier (more dense, sinks below oil) it will go under, and as it begins to boil, the blobs or water become air pockets that rise and burst
Oil has higher boiling point than water.
Oil into boiling water -> oil heats up, nothing happens.
Water into boiling oil -> water almost instantly vapourizes, expanding rapidly and carrying oil droplets with it (which often ignite if there’s an open flame nearby).
1. Hot oil is simply way hotter than boiling water.
2. Water is denser than oil, so it sinks.
For a pot of boiling water, it is at its **maximum** temperature and literally no hotter temp exists for it (it has to transform into steam and leave the pot to get hotter). From the perspective of oil, boiling water is just fairly hot. The oil will float on top and you just have oily boiling water.
For a pot of hot oil, it could get very hot, far beyond the boiling point of water. If you pour water into really hot oil, well, from the perspective of water, the temperature is hotter than is physically possible, and it will turn into steam. This *might* have been kinda safe if the water was able to float on top of the water, but it doesn’t: the water both *sinks* and *explodes into steam* at the *same time*.
For reference, when measured in Celcius, water is liquid from 0C to 100C. Under 0 it freezes, over 0 it boils into steam. Hot oil can maybe get as hot as 200C if it is around its smoke point. It would be inaccurate to call that ‘twice as hot as boiling water’, but it is ‘twice the difference in temperature between frozen water and steam’. (You usually wouldn’t cook with a bot of oil at smoking point, but the point remains that you can go hotter than 100C.)
Water sinks, boils, turns to steam and rises rapidly causing the explosion of boiling oil. Oil is heavier than water and boils but doesn’t change it’s state so it just stays where it is but really hot.
Boiling oil is much hotter than water’s boiling point. Throw water into boiling oil and it instantly vaporises into a cloud of steam. That instant boiling takes the oil with it, like a huge splash, and now you have a cloud of extremely hot oil droplets.
If that oil was actually on fire, then instead of just the surface oil burning slowly you suddenly have millions of tiny droplets burning very fast over a very large volume. This is very bad.
Add cold oil to boiling water and nothing happens because the oil doesn’t boil. You just get hotter oil and maybe cooler water. It’s not the evaporating oil that burns, it’s the violent vaporization of water throwing the oil on the air that causes fires. If you somehow had the water under so much pressure that it was still liquid well above the oil’s flash point (the temperature it combusts) when you dump in the oil, the you might be able to get a similar fireball but at those pressures the oil wouldn’t want to vaporize either, and releasing the pressure would explosively boil the water anyway
Energy density.
Heat is a biproduct of energy transference. Energy density speaks to how much energy a material can have before it changes states. Oil takes more energy to change states from a liquid to a gas than water does.
Energy also likes to equalize so when a material with a lot of energy touches an energy with not much energy, the energy transfers from one to the other until they reach an equilibrium (if they can reach an equilibrium). We observe this in the kitchen with heat.
Since Oil takes a lot of energy to change state it holds a lot of energy. It coincidently holds enough energy that, while “hot enough”, it can transfer enough energy per second to have the amount of energy being put into the water reach that state-changing threshold requirement, and the water (near-instantly) changes state from liquid to gas. That gas takes up more space than the water did, and explodes outward from the oil.
It should be noted that this may still occur in a pot of oil that’s below the temperature of water boiling because of the energy density taking more energy to get the oil’s temperature to reach that level (degree of temperature), than it takes water.
Since oil has a higher energy density capacity than water, and takes more energy to change state, dropping oil into boiling water (water in the process of changing state) it reaches an energy equilibrium but does not change state itself.
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