What causes ice to melt?

• A. The release of heat energy
• B. A decrease in temperature
• C. The addition of pressure
• D. The absorption of heat energy

Answer: (D)

Melting happens when heat energy is absorbed by the ice. This energy goes into breaking the strong hydrogen bonds that hold the solid structure together, allowing the molecules to move past one another as a liquid. At the melting point, the temperature can stay at 0°C while the ice absorbs heat, because that energy is used as latent heat of fusion rather than increasing the temperature. Once enough energy has been absorbed to overcome the lattice, the ice becomes liquid water, and additional heat then raises the water’s temperature. Releasing heat would promote freezing, reducing temperature slows or stops melting, and while pressure can influence the melting point, the fundamental cause of melting is the absorption of heat energy.