Ray puts a glass of ice water on the table. One hour later he observes that only water is left in the glass. What happened?

The ice in the glass melted into liquid water (a physical change, known and change of phase)

Explanation:

Heat flows from warmer substances to cooler substances.

Ice water contents ice (solid water) and liquid water.

Ice freezes at 0°C and below.

Ice is the solid state of water; at this stage, the water molecules have low kinetic energy and the remain vibrating around a relatively fixed position in a crystal structure.

The liquid water around the solid ice cubes has a larger kinetic energy than the cubes. Also, the environment is at a higher temperature than the content of the glass.

Hence, both heat from the room and heat from the liquid water will flow toward the cooler ice cubes. The molecules that form the ice cubes will gain kinetic energy, causing the temperature of the ice cubes increase; the molecules will vibrate faster until they can move and slide past each other, which means that they have become liquid (melted).

This is a physical change known as change of phase, specifically melting.

Ice Water