Why water explodes in microwave

Superheated water is extremely dangerous and nothing to play around with. Superheating is a physical reaction that is sometimes referred to as boiling retardation or boiling delay. The phenomenon occurs when water is heated to a temperature above the boiling point without actually boiling.

How does water exceed the boiling point and not boil? Microwaves heat water unevenly, and the water temperature gets poorly distributed throughout the liquid. Boiling hot water and steam vapor can get trapped underneath a layer of cooler water temperatures. The surface tension strengthens the water pressure and acts as a barrier that traps in hot water and steam vapor allowing it to become superheated.

Water can heat above the boiling point when held under pressure and pockets of steam vapor can develop. Microwaves use electromagnetic radiation to heat water molecules extremely rapidly. As a result, water heats unevenly and some pockets of water heat up faster than others.

Microwave water can explode when it is superheated, or vaporized below areas with cooler temperatures. Large bubbles of water vapor quickly form underneath the surface tension and when the cup or container is shaken the water can erupt in a violent explosion. These become nuclei for boiling. Even a crack that is fully filled with water can be a boiling nucleus because it reduces the required area of the water-vapour surface.

This is only 1. Those three litres of steam are created inside the hot water, quite suddenly, so the water is ejected violently from the container. If it were possible to turn the oven on with the door open, a beam of microwaves would radiate through the open door. This beam would be dangerous: it would rapidly heat up human tissue just like cooking meat and could have other health effects as well.

Never disconnect the automatic safety switch If the door or the case of the oven are damaged, either discard the device or have it checked for microwave leakage. Some sites with related material I wrote an article about this for The Science Teacher.

Mpemba effect: can hotter samples freeze faster than cold? What is 'unfreezable water'? Supercooling, rather than superheating, is sometimes involved. Despite its ubiquity, water is a remarkable and unusual chemical. See Martin Chaplin's page: Water structure and behaviour. Boiling and freezing: the effects of solutes and of pressure. A list of other educational pages in physics by Joe Wolfe.

Originally set up for teachers and students using the New South Wales syllabus. Happy birthday, theory of relativity! As of June , relativity is years old. Our contribution is Einstein Light: relativity in brief It explains the key ideas in a short multimedia presentation, which is supported by links to broader and deeper explanations.

Superheating and microwave ovens There have been many reports of injury to people using microwave ovens to heat water to make hot drinks. Some quantitative details More about boiling and freezing temperatures Other potential dangers associated with microwave ovens When does it happen?

The following conditions promote these potentially dangerous events: Using a container with a very smooth surface, such as an unscratched glass or glazed container. Heating for too long. Quickly adding a powder, such as instant coffee or sometimes even an object to stir it.

Standing with one's face above the container makes injury more likely. How it could be dangerous : You put water in a new mug one that has no cracks in the internal glazing and which has never been scoured.

You put it in the oven with a setting that is a little too long for the amount of water. While it is heating the phone rings. You return some time later, decide to reheat it, so you restart the oven. You take out the cup and immediately add a spoonful of instant coffee. While making tea in a microwave isn't ideal because you can't control the temperature, if you need to use the microwave instead of a kettle, stick a chopstick, dowel, or other stick in the cup just in case.

Relax and be free from anxiety Take back good sleep and help alleviate pain. Photo by selena marie. Distilled water will never boil. It will absolutely superheat in the microwave and explode in your face.