12.2.2 CIA Demonstration: Boiling Water at Reduced Pressure

Question 1

CIA Demonstration: Boiling Water at Reduced Pressure

Answer 1

• Boiling occurs when the vapor pressure equals the atmospheric pressure.
• At low atmospheric pressure, the boiling point of water is lower.

Question 2

note

Answer 2

• Food takes longer to cook at high altitudes because water boils at a lower temperature at higher elevations. Boiling occurs when the vapor pressure equals the atmospheric pressure.
• This decrease in boiling point is because there is less
  atmosphere pushing down on the water, and so less
  vapor pressure is exerted on the surface of the liquid.
• The lower boiling temperature reflects the decrease in the energy required to make the vapor pressure equal to the atmospheric pressure.
• In this experiment, a filter flask is attached to a water
  aspirator. Water in the flask is heated by a hot plate, and a thermometer is used to measure the temperature. The water aspirator lowers the atmospheric pressure in the flask.
• The water aspirator lowers the atmospheric pressure in the flask. When the atmospheric pressure is lower, the boiling point is lower (80 ̊C in this experiment, versus 100 ̊C at one atmosphere of pressure).