When ice melts, the heat absorbed by the ice causes the water molecules in the solid state (ice) to gain energy. This increase in energy allows the molecules to overcome their rigid structure and transition to the liquid state.
In this case, since Cynthia notices that most of the ice in her iced tea has melted, it indicates that the temperature of the surrounding water (the iced tea) is higher than that of the ice, leading to heat transfer. The particles in the ice vibrate more rapidly as they absorb heat from the surrounding liquid, breaking the hydrogen bonds that hold them in a fixed structure, and allowing them to move more freely as liquid water.
In summary, the particles in the ice absorbed energy, increased their kinetic energy, and transitioned from a solid to a liquid state as the ice melted.