Explain why the potential energy increases when ice starts to melt and becomes liquid water
When ice starts to melt and become liquid water, its potential energy increases because the arrangement of water molecules changes. In ice, water molecules are arranged in a crystalline structure with each molecule bonded to a fixed number of neighboring molecules through hydrogen bonds. The hydrogen bonds in the solid ice lattice help to hold the molecules in a specific arrangement, giving it a relatively ordered structure.
However, when ice melts and becomes liquid water, the hydrogen bonds break and the water molecules gain more freedom to move. These molecular movements result in an increase in the potential energy of the system.
As the ice melts, energy is required to break the hydrogen bonds and overcome the intermolecular forces holding the solid structure together. This energy, known as the enthalpy of fusion, is absorbed from the surroundings. It allows the water molecules to move more freely and spread out, resulting in an increase in potential energy.
The increase in potential energy during melting can be understood from a molecular perspective. In the solid state, the water molecules are relatively fixed in their positions, with limited degrees of freedom. As the ice melts, the water molecules gain more freedom to move and arrange themselves in a less ordered manner. This increased movement and disorder contribute to the higher potential energy of the liquid water compared to the solid ice.
It is important to note that the increase in potential energy during the melting process is reversible. If liquid water is cooled below its freezing point, the potential energy decreases as the water molecules rearrange into the more ordered solid ice structure.