# What Is the Equation of Heat of Fusion?

The equation for the heat of fusion is ΔH=nΔHfus, where "n" is the number of moles and ΔHfus is the molar heat of the substance. Heat of fusion, also known as enthalpy of fusion, is the required amount of energy, needed for matter to change from a solid to a liquid without an increase in the temperature of the matter. The heat of fusion is represented in mathematical notation as "H."

States of Matter
Matter is anything that has mass and takes up space. It is everything that makes up the physical things present in the universe. There are five known states of matter: solids, liquids, gases, plasma, and Bose-Einstein condensates. Each state of matter is distinguished by the density of the particles it is composed of. While solids have very tightly packed particles, the particles in liquid matter are much less dense.

Changing States
When matter is exposed to energy, it can change from one state to another. Energy is defined as the potential for change, and can take several different forms, such as thermal and electric. When solid matter is exposed to thermal energy, or heat, it can transform into a liquid or a gas. Conversely, when thermal energy is removed from a liquid, it can transform back into a solid. This process describes how water melts and freezes as the temperature rises and falls.

Heat of Fusion
Each substance has a different heat of fusion, depending on the melting point of that substance. Heat of fusion is measured either in Joules per gram (J/g) or calories per gram (cal/g). When a substance such as water melts from a solid state to a liquid state, the heat of fusion is positive. Conversely, when it changes from a liquid to a solid, the heat of fusion is negative.

Practical Applications
Knowledge about the heat of fusion and melting points of different substances can prove to be useful. An industrial application of the equation for heat of fusion is coin making, during which metals such as zinc and copper are transformed from a solid state to a liquid state, reshaped, and changed back into a solid state. Other occupational applications of the heat of fusion application are plastics molding, glass blowing, and metal forging.

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