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Why Does Temperature Affect the Rate at Which Something Melts?

Sipping a cold glass of lemonade becomes a race against time on a warm day, when the ice begins to melt before the drink is halfway consumed. Humans use temperature on a daily basis in the kitchen, on roadways and in science labs to initiate the melting process, paying little attention to how the phenomenon of melting actually works. To understand what makes a substance melt at a certain temperature, first consider energy and physics.

Physics of Melting
- When something melts, it changes states from a solid to a liquid; it does not change its identity. For instance: water, water vapor and ice are all variations of the same substance --- H20 --- at different states. Changing from one state to another requires energy, and that energy comes in the form of heat, produced when the temperature increases. When heat is applied, the atoms of a substance contract and condense, so that the substance "melts" into a liquid and occupies less area.
Factors of Melting Point
- The temperature at which a substance melts depends on several things. The purity of the substance affects its melting point. Pure solids melt over a narrow span of temperatures, and substances that are mixed --- containing two or more elements --- melt over a wider range of temperatures, which tend to be below the melting points of the pure solids. Defects also affect the melting point. In the example of ice, cubes of ice with external or surface cracks melt more quickly than smooth ice, because melting begins at the defects.
Practical Applications
- The natural phenomenon of heat initiating melting has several applications. Consumer products like freezers, coolers and thermoses are designed to maintain an object's temperature to prevent state changes --- melting and freeing --- from occurring. Other inventions aim to speed up the processes. The heated driveway was conceptualized to speed up the melting of snow, and the Fondu pot, with an adjustable temperature, works by keeping solid food items, such as chocolate and cheese, in their respective liquid states.
Melting Temperature Identification
- Scientists have adapted the idea of a melting temperature into a method of identification for solids and compounds. In a controlled lab setting, experimenters place an unidentified substance over a heat source with an attached thermometer and wait for it to melt, recording the temperature at which the change occurs --- the melting point. Based on the melting point, the scientist can decipher the name of the substance. For example: glucose sugar melts at 150 degrees Celsius, while fructose melts within the range of 103 to 105 degrees.

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