The phenomenon in which a liquid changes into gas, or a solid changes directly into gas. Vaporization from the surface of a liquid is called evaporation, while vaporization from the inside is called boiling. Vaporization from the surface of a solid is called sublimation. At a given temperature, vaporization progresses until the vapor pressure of the surrounding gas phase reaches the saturated vapor pressure or sublimation pressure, and then equilibrium is reached. Heat is required for vaporization, and the latent heat is called the heat of vaporization, which varies depending on the temperature. The heat of vaporization is also called the heat of evaporation for liquids and the heat of sublimation for solids. Microscopically, vaporization is a phenomenon in which a small number of particles (molecules and atoms) in a cohesive state (liquid and solid) that are in thermal motion gain large kinetic energy due to statistical fluctuations, overcome the cohesive force from the surrounding particles, and fly out from the surface to become a gas. The heat of vaporization, which indicates the strength of the cohesive force, decreases as the temperature increases. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
液体が気体に,または固体が直接に気体に変る現象。液体の表面からの気化を蒸発,内部からの気化を沸騰といって区別する。固体の表面からの気化は昇華と呼ばれる。与えられた温度において,気化は周辺の気相の蒸気圧が飽和蒸気圧または昇華圧になるまで進行して平衡に達する。気化するには熱を要し,その潜熱は気化熱と呼ばれ,温度によって異なる。気化熱は液体では蒸発熱,固体では昇華熱とも呼ばれる。微視的には,気化は凝集状態 (液体と固体) にあって熱運動している多数の粒子 (分子や原子) のなかで統計的ゆらぎによって大きい運動エネルギーを得た少数個の粒子が,周囲の粒子からの凝集力にうちかち,表面から飛出して気体となる現象である。その凝集力の強さを表わす気化熱は温度が高くなるほど小さくなる。
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