To liquefy means to turn something solid into a liquid, usually by heating it. When you leave a chocolate bar in your pocket on a hot day, the chocolate liquefies into a messy puddle. When a chef liquefies butter in a pan, it changes from a solid yellow stick into a golden liquid that can coat vegetables or blend into a sauce.

The transformation happens because heat makes the molecules in a solid move faster and spread apart until they flow like a liquid. Ice liquefies into water when temperatures rise above 32 degrees Fahrenheit. Metal workers liquefy iron in massive furnaces, heating it to over 2,800 degrees Fahrenheit so they can pour it into molds to make everything from car parts to skyscraper beams.

Scientists and engineers also liquefy gases by cooling them to extremely cold temperatures and putting them under enormous pressure. They liquefy natural gas to make it easier to transport across oceans in special ships, since liquid takes up much less space than gas. The related noun is liquefaction, which describes the process itself, like when geologists study soil liquefaction during earthquakes.