The photos below illustrate an experiment you can do...

The photos below illustrate an experiment you can do yourself. Place $10 \mathrm{mL}$ of water in an empty soda can, and heat the water to boiling. Using tongs or pliers, turn the can over in a pan of cold water, making sure the opening in the can is below the water level in the pan. a.(FIGURE CAN'T COPY) b.(FIGURE CAN'T COPY) (a) Describe what happens, and explain it in terms of the subject of this chapter. (b) Prepare a molecular level sketch of the situation inside the can before heating and after heating (but prior to inverting the can).

The photos below illustrate an experiment you can do yourself. Place $10 \mathrm{mL}$ of water in an empty soda can, and heat the water to boiling. Using tongs or pliers, turn the can over in a pan of cold water, making sure the opening in the can is below the water level in the pan. a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
(a) Describe what happens, and explain it in terms of the subject of this chapter.
(b) Prepare a molecular level sketch of the situation inside the can before heating and after heating (but prior to inverting the can).

Key Concepts

Phase Change

Phase change refers to the transformation of a substance from one state of matter to another, such as from liquid to gas (boiling) and back from gas to liquid (condensation). In this experiment, water undergoes phase changes as it is heated to boiling, creating water vapor, and then cooled rapidly, causing the vapor to condense back into liquid form.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its liquid or solid phase at a given temperature. When the water is heated, its vapor pressure increases until boiling occurs; upon rapid cooling, the vapor pressure drops significantly, contributing to the collapse of the can as external atmospheric pressure exceeds the reduced pressure inside.

Atmospheric Pressure

Atmospheric pressure is the force per unit area exerted by the weight of the air in the Earth's atmosphere. In the experiment, after the water vapor condenses, the minimal internal vapor pressure is unable to counteract the external atmospheric pressure, leading to the implosion of the can. This demonstrates the powerful effect of atmospheric pressure when a vacuum or low-pressure area is created.

Kinetic Molecular Theory

The kinetic molecular theory explains the behavior of gases in terms of the motion of their molecules. As water is heated, the increased kinetic energy of the molecules allows them to overcome intermolecular forces to form vapor. Conversely, when the vapor is cooled, the loss of kinetic energy causes the molecules to come closer together, leading to condensation. This transition explains the changes observed in the experiment at a molecular level.

Condensation

Condensation is the process by which a gas transitions into a liquid when its temperature is lowered or pressure is increased. In the experiment, as the can is cooled, the high-energy water vapor loses energy, leading to the formation of liquid water. This rapid condensation reduces the number of molecules in the gaseous state, which in turn decreases the internal pressure and allows atmospheric pressure to crush the can.

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