A one gallon kettle is completely filled with water sealed and heated as wate - HiSET Prep

Correct Answer: a. The volume of water increased when it boiled, destroying the kettle. When water is heated in a sealed, completely full container, it begins to change phase from liquid to gas once it reaches its boiling point. Water vapor (steam) occupies much more volume than liquid water at the same temperature and pressure. However, because the kettle is sealed and rigid, the expanding steam cannot escape or expand freely. Instead, pressure inside the kettle rapidly increases as more water molecules try to enter the gas phase. The metal walls experience growing internal force, first bending, then rupturing when the pressure exceeds the kettle’s strength. The key cause is that boiling water produces gas that requires more space; in a confined, sealed system, this increase in volume manifests as dangerously high internal pressure, which ultimately causes the kettle to explode.

Why Other Options are Incorrect:

• b. The temperature of the kettle increased, inducing a phase change in the kettle.
  Though the kettle does heat up, most kitchen metals do not undergo a phase change (like melting) at water’s boiling temperature. The kettle bends and explodes due to internal pressure, not because the metal itself changes state. This explanation confuses the heating of the container with the real issue: expanding steam in a sealed vessel.

• c. The pressure on the kettle decreased, causing the kettle to expand and burst.
  Pressure inside the kettle actually increases, not decreases. As water turns to steam in a confined space, internal pressure rises, pushing outward on the walls. A pressure decrease would not cause explosive failure in this context. Therefore, this option gets the direction of pressure change exactly backwards.

• d. The density of the water increased, bursting the kettle.
  When water turns into steam, its density dramatically decreases because the same mass occupies a larger volume. Increased density would mean the water becomes more compact, which would not explain expansion and explosion. The problem is expanding gas at lower density in a confined volume, not increasing density.