For a liquid to change into a solid, heat energy must be removed. The process of removing heat energy from a substance, causing it to lose thermal energy and transition from a liquid to a solid state, is called solidification or freezing. When the temperature of a liquid reaches its freezing point, the removal of heat energy causes the particles within the liquid to slow down and arrange themselves into a more organized and fixed structure, forming a solid. The removal of heat allows the particles to decrease their kinetic energy, leading to a decrease in intermolecular motion and the formation of a solid crystal lattice.