The Magic of Steam… Unit 3


Water 1 Vapor 1600

einstein cartoon right looking

When WATER is heated to the boiling point at atmospheric pressure and you boil away all the water, it will expand into about 1600x larger volume of VAPOR.

When water and the red hot inside of the earth meet the water immediately becomes vapor and exapmd 1600 times into a spectacular volcanic explosion

energy Littoral_explosion_at_Waikupanaha_2


In a test tube 3 cubic centimeters of water is heated and boiled away with a gas burner. It will blow up a balloon to about 1500 cubic centimeters, the size of a 1.5 liter soft-drink bottle, or 500 times.

steam balloon

Five hundred times is a lot, but it is not equal to the theoretical number of 1600 times? Because…

While we blow up the balloon, there is CONDENSATION on the inside of the balloon because the temperature around the balloon is less than 100 degrees Celsius.


energy condensation

When you blow against a cold window pane the water vapor in you breath condenses in small water droplets against the glass. On  a cold day you can blow on the lenses of your glasses and they fog up, same thing or phenomenon….

Back to the steam inside the balloon: the water vapor or steam in the balloon cools inside against the wall of the balloon and becomes water; therefore, we have less steam and this experiment can never show the theoretical number of about 1600x expansion.

Still it is fun!

When we take the test tube away from the heat source, the balloon starts to shrink, WHY?
Water runs back into the test tube, WHY?
Think of the C-word…

The Boiler is ready…

steam pressure cooker blow off

The boiler, just a household pressure cooker, is ready to boil the water and make
STEAM and …BLOW OFF, like a geyser!

But first: in the pressure-cooker, water is boiling at 120 degree Celsius.

120 Degrees Celsius ?

I thought water boiled at 100 degrees Celsius? Yes, true, but remember, on top of a mountain it boils at less than hundred degrees? Remember? Know why?

It is the opposite inside the pressure-cooker, there is a higher pressure than the normal atmospheric pressure around us, and therefore
water boils at a higher than 100 degree temperature.

The pressure inside the pressure cooker is controlled by the weight of the pressure valve and is one atmosphere higher than the air pressure around us.
That makes the water boil at 120 degrees Celsius.

steam press cooker gage

The pressure meter or gage shows 15, this is fifteen pounds per square inch, an old fashioned Imperial measure, it is the same as one atmosphere, the same pressure we feel around us, BUT as the gage shows, inside the boiler it is one atmosphere higher than around us and that means that water boils at a higher temperature, 120 degrees Celsius!

In THERMODYNAMICS books and tables, you can look up any pressure and boiling temperature of water or other liquids; scientists and engineers have figured this all out!

We have added to the boiler a valve that we can close and open. When the water inside the pressure cooker is boiling, there is water AND water vapor or steam inside with a pressure of one atmosphere above our environment. It would like to get out: EXPAND.  When we open the valve it blows of like a little volcano!


The heat energy from the electric hot plate made the water inside the pressure-cooker boil. Water and steam, two phases of water, exist together inside the boiler.

There is a lot of POTENTIAL ENERGY inside the boiler and that energy can do WORK.

Time for work…Go to unit four.


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