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 so-called "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

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