Question

which statement about the physical change of liquid water boiling into steam is true?
the heat added represents an energy change.
the action cannot be reversed.
the steam cannot conserve mass.
the weight lost represents a mass change.

Explanation:

• Boiling water to steam is a reversible physical change; cooling steam turns it back to liquid water, so the "cannot be reversed" statement is false.
• The law of conservation of mass applies to physical changes: the total mass of water (liquid + steam) remains the same, so the "steam cannot conserve mass" statement is false.
• Weight loss (if measured in an open container) is due to steam escaping, not a change in total mass, so the "weight lost represents a mass change" statement is false.
• Adding heat to boil water is an energy transfer (thermal energy is used to break intermolecular bonds for phase change), so this energy change is real.

Answer:

A. The heat added represents an energy change.