Why Is Steam Hotter Than Boiling Water

Why is steam hotter than boiling water? How can you show your child the water to steam and back to water process?

It may fascinate your child to learn that steam is hotter than boiling water, especially when your child learns that pressurized steam can actually get up to 700 degrees Fahrenheit, which is far hotter than the 212 degrees boiling water reaches. You can help your child understand how this process works by doing the following activity and sharing the following information.

A Simple Kitchen Experiment
Place a pot of water on the stove and turn the heat on high. Insert a candy thermometer in the pot of water and keep an eye on the temperature as the water heats up.

As the water begins to boil, explain to your child that the temperature of the water will max out at 212 degrees Fahrenheit because the water is changing form. It is converting to steam, changing from a ratio of 100% water to 0% steam to a ratio of 100% steam and 0% water. This change does not happen immediately when you heat water on your stove. If you were able to immediately heat the water to a temperature of 212 degrees, you would have an instant transformation to steam.

A stove isn't powerful enough to instantly create steam; instead, the water in your pot is heating from one source of heat under the pot, and some of the water molecules are hitting the boiling point temperature sooner than other molecules. The heat is transferred from water molecule to water molecule. As each molecule hits 212 degrees, it turns into steam, but this happens relatively slowly.

You can vary this experiment by setting different pots of water on different burners and seeing how long it takes different levels of heat to turn all the water into steam. Discuss the varying factors involved: the type of metal the pan is made from, the size of the pan, the size of the burner, how deep the water is in the pan and how the amount of surface area exposed to the source of heat makes a difference in how fast the water evaporates.

Try adding different ingredients to the water to see if it will change the boiling time. You can add salt to one pot and baking soda to another and see if there is any difference in boiling time and evaporation time when compared to a pot of plain water. Try covering a pot of water and testing the boiling time and how long it takes the pot of water to evaporate; this will allow you to explain how the steam condenses on the lid of the pot and returns to the pot of water as water droplets, then evaporates again.

As you do these experiments, point out that the water, in liquid form, does not get hotter than 212 degrees Fahrenheit. Why is this? Because water turns to steam at this heat. It can never get any hotter without becoming steam.

Steam, if properly heated, pressurized and contained so that it does not condense back into water, can be heated to hundreds of degrees hotter than the boiling point of water. Steam can exist up to temperatures of about 700 degrees Fahrenheit. Above that temperature, the bonds between the hydrogen and oxygen atoms that make water molecules break, creating pure hydrogen and oxygen gases. 

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