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:

1. Analyze the first option: When liquid water boils into steam, heat is added. This heat is used to change the state of water from liquid to gas, which is an energy change (specifically, heat energy is absorbed to overcome intermolecular forces).
2. Analyze the second option: The process of water boiling into steam is reversible (by condensing steam back into liquid water), so this statement is false.
3. Analyze the third option: According to the law of conservation of mass, mass is conserved in physical changes. So steam (water vapor) does conserve mass, making this statement false.
4. Analyze the fourth option: Weight is related to mass and gravity. When water boils, the mass of water remains the same (it just changes state), so there is no mass change, and thus no weight change due to mass change (weight change could be due to other factors like pressure, but not mass here), making this statement false.

Answer:

The heat added represents an energy change.