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In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure.
26 cze 2023 · The heat which a solid absorbs when it melts is called the enthalpy of fusion or heat of fusion and is usually quoted on a molar basis. (The word fusion means the same thing as “melting.”) When 1 mol of ice, for example, is melted, we find from experiment that 6.01 kJ are needed.
The specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher.
The heat of fusion is the enthalpy change when a unit mass of a substance changes its state from solid to liquid at a constant temperature and pressure. It is sometimes called enthalpy of fusion or latent heat of fusion.
The enthalpy of fusion of water is about 334 J/g, i.e., 334 joules of energy are needed to change each gram of ice at 0 degrees Celsius into water. This is important for understanding energy balances in large ice formations like glaciers and polar ice caps.
The amount of energy to change 1 g of solid to liquid at its melting point. For water, \Delta H_{{\rm fus H}_2{\rm0}} = 80 {\rm\ cal\ g}^{-1}.
Scientists deal with this by defining a new constant called the heat of fusion : heat of fusion = q / m. The heat of fusion has units of J/g. Different substances have different heats of fusion. The heat of fusion of water at 0 ºC is 333 J/g, for example.
