

Liquid to Gas Volume
Name: Clarence
Status: other
Grade: other
Location: IL
Country: N/A
Date: 7/9/2005
Question:
I am 84 wondering how much a cubic inch of water will
expand when turned into steam that is saturated how much does it expand
when superheated
For that matter is there any kind of general relationship for any volume
of liquid, such as liquid nitrogen, becoming a certain volume of gas?
Replies:
The socalled "ideal gas law": P*V = n * R * T where P is the pressure in
atmospheres, V is the volume in liters, n is the number of mols which is
equal to gm / MW (where gm is the weight of the amount of gas and MW is the
molecular weight (for water MW = 18), and T is the temperature in kelvins:
T = C + 273.15 where C is the temperature in degrees Celsius, and R = a
constant = 0.082 liter * atm / mol * kelvins. For water at its boiling
point, (100 C = 373.15 kelvins), P = 1 atm; choose
n = 1 so that gm = 18 and MW = 18, and T = 373.15 and R = 0.0825 l * atm /
mol * kelvins, so:
V = 0.082 * 373.15 / 1(atm) = 30.6 liters. This is a large expansion because
18 gm water = 18 cm^3 =
0.018 liters that is an increase in volume of about 1700 times!
Vince Calder
At standard pressure, gasses expand linearly from absolute zero. (so a
given amount of gas at 200 degrees Kelvin will double in volume at 400
degrees Kelvin.) Liquids and solids expand and contract as well, but to a
much smaller degree.
At anything remotely near room temperature, (including your stove, oven, or
freezer), one rule of thumb says you are looking at about 1,000 times
expansion in volume. Heating water without permitting the steam to expand,
or not allowing it to expand very much, allows the creation of relatively
high pressures. Further heating the steam (superheating) again will
increase its volume or pressure linearly from absolute zero.
Ryan Belscamper
Click here to return to the Physics Archives
 
Update: June 2012

