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Water always boils at 100 °C, right? Not always! Water boils at 100 °C at 1 atmosphere of pressure. Every liquid boils at the temperature at which its vapor pressure equals the pressure above its surface. Change the pressure, and the required boiling temperature changes! Explore both phase change and vapor pressure in this very dramatic demonstration. By decreasing the vapor pressure inside the syringe, hot water can be boiled at less than 100 °C. As the water boils, the vapor is pressurizing the area above the liquid. The water will continue to boil until the pressure equals that of the vapor pressure or until no liquid is left. Includes Teacher Demonstration Notes, reproducible student handouts and a detailed discussion section.
Concepts: Vapor pressure, boiling, phase change. Time Required: 10 minutes Materials Provided: Demonstration syringe (120-mL) and stopcock with Luer Lock adapter
Materials Included in Kit:
Demonstration syringe, 120 mL
MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.