Which statement describes the energy change when a solid becomes a liquid?

• A. The substance gains energy.
• B. The substance loses energy.
• C. The energy remains the same.
• D. The energy causes temperature to rise.

Answer: (A)

When a solid becomes a liquid, it must overcome the forces holding the molecules in a fixed arrangement. This requires energy input, so the system absorbs energy from the surroundings. That energy goes into breaking those intermolecular forces and allowing particles to move more freely as a liquid. For a pure substance at its melting point, this energy input doesn't raise the temperature; it goes into the phase change itself. Only after melting is complete would additional energy start to raise the temperature again. So, the energy change during melting is an intake of energy.