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:

• When liquid water boils into steam, heat is added. This heat is used to break the intermolecular forces in water (liquid) and convert it into steam (gas). So, the heat added represents an energy change.
• Boiling of water is a physical change and can be reversed (by condensation).
• According to the law of conservation of mass, mass is conserved in physical changes. Steam (water vapor) has the same mass as the liquid water (if we consider a closed system).
• The weight lost (if any, due to evaporation in an open system) is just water changing its state (from liquid to gas), not a mass change (in a closed system, mass is conserved).

Answer:

The heat added represents an energy change.