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Boiling Liquids at Reduced Pressure. Acetone is boiled without heating. Purpose. To boil acetone using an alternative method. To boil acetone below its normal boiling point. Demonstration. Acetone will be made to boil by reducing the vapor pressure. Concepts. Reduced Pressure
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Boiling Liquids at Reduced Pressure Acetone is boiled without heating.
Purpose • To boil acetone using an alternative method. • To boil acetone below its normal boiling point.
Demonstration • Acetone will be made to boil by reducing the vapor pressure.
Concepts • Reduced Pressure • Boiling Point • Entropy
Reduced Pressure • External pressure above the liquid is reduced. • Reducing external pressure, reduces the vapor pressure needed to induce boiling .
Boiling Point • Point at which vapor pressure of liquid slightly exceeds the external pressure above liquid. • The reduction in vapor pressure allows acetone to boil below it’s normal boiling point.
Entropy • A measure of disorder or randomness in a closed system. • Boiling causes molecules of the liquid to be converted from an ordered liquid state to a disordered gas state, increasing the entropy of the system.
Conclusions • By reducing external pressure above the liquid, the vapor pressure is also reduced. • At boiling point, the vapor pressure is slightly more than the external pressure. If external pressure is reduced, the boiling point will occur at a lower temperature than normal.
Comments • Cooking at High Elevations • atmospheric (external) pressure higher • boiling point of water is lower • food cooks more slowly at lower temperatures