什么是熔点?
这件事的特点是不同的状态。可以从一种物质状态过渡到另一种物质状态。例如,固体可以转化为液体,液体可以转化为气体。例如,大多数固体金属在加热时变成液体,在进一步加热时变成蒸气。
物质状态的变化,例如,从固态到液态的发生是由于以下两个特征因素:
- 温度——随着温度的变化,会发生从固态到液态的转变,即温度的升高。随着温度的升高,冰变成了水。此外,液体变为蒸汽状态。冰 → 水 → 蒸汽
- 压力——固体的特点是颗粒紧密堆积,它们之间没有空隙。它们不允许任何压缩,因此,压力对固体没有影响。在不断施加压力时,固体会变形并最终破裂。
从固体到液体的转化
The process of a solid turning into a liquid state is called melting. It is also known as fusion. The reverse process of a liquid becoming a solid, is in turn called solidification.
任何纯物质发生熔化的温度称为该物质的熔点。它被认为是该物质的特征。系统需要能量来将固体熔化为液体。这是一个吸热反应。每种纯物质都需要一定的能量才能从固态变为液态。
能量只需要进行物质从固体到液体的转变。物质的相发生变化,温度保持不变。因此,众所周知,熔化是一个等温过程,因为物质保持在相同的未改变温度。
融化
熔化或融合是固体物质在加热时变成液体的过程。在加热物质时,粒子以更大的强度振动并且更剧烈地移动。产生热能。粒子获得足够的动能来克服强大的吸引力。它们获得能量以突破以形成小的粒子群。因此,固体熔化形成液态。
物质的熔化发生在规定的环境压力条件下。熔化系统所提供的能量称为融合焓或融合熵。然而,一些物质对这个过程构成了一个例外,必须从这些系统中去除热量才能熔化它们。例如氦气。
什么是熔点?
The temperature at which a solid substance melts and transforms into a liquid at atmospheric pressure is termed the melting point of a substance.
不同的固体表现出不同的熔点。例如,蜡的熔点为 63 °C。物质的熔点越高,结合粒子的粒子内吸引力就越大。例如,在水的固态形式中,冰在 0°C 的温度下融化形成液态水。因此,大气压下冰的熔点为0°C。
在熔点处,物质的固态和液态共存。物质的熔点是其受施加压力影响的特性。
Applications of Melting Point
The application can be observed during the process of snow skating. The weight of the skater gets concentrated on a thin line, there is considerable pressure applied on the ice slab. This results in the melting of ice beneath the shoe of the skater. This melting ice lubricates the undersides of his skating shoes. This makes it possible to skate on the ice.
固体转化为液体的加热曲线
加热曲线分别表示 y 轴上的温度和 x 轴上已提供的热量。让我们假设一个恒定的加热速率,因此 x 轴可以显示为物质被加热时显示的时间量。曲线主要显示两个要点:
- 图表的一部分,当向系统提供热量时温度升高,以及
- 图表中温度保持在恒定水平的平台部分。相位变化发生在这个高原。
示例问题
问题1:是什么导致相变?
回答:
When the temperature or pressure change of a system occurs, the phase changes. Upon increasing the temperature or pressure of the system, the intramolecular forces of attraction increase. Upon decreasing the temperature, the molecules or atoms turn into a rigid structure.
问题2:加热冰的过程中温度会发生变化吗?
回答:
As we constantly supply heat energy to transform ice into water, the temperature of the system doesn’t change. The heat energy is absorbed by the ice changing slowing into the liquid state. Both the states of matter coexist together during this process.
问题 3:在无定形固体的情况下如何发生熔化?
回答:
The non-crystalline solids, such as glass or pitch undergo melting by slowly decreasing viscosity with the simultaneous increase in the temperature. However, there is no sharp transformation from solid to liquid state.
问题 4:定义熔化热。
回答:
The amount of energy required by a pure substance to change from the solid to a liquid state is termed as the enthalpy of fusion (or heat of fusion) of the substance. It is denoted by ΔHfus.
问题5:区分沸腾或熔化。
回答:
Boiling is the process of melting of liquid to gas state whereas melting is the transformation of solid to liquid state.
问题6:熔化过程中如何发生能量变化?
回答:
Heat must be supplied to the enclosed system in order to simulate the melting of the substance. When energy is supplied the atoms composing the substance break away and are pulled apart farther.
问题7:哪种元素的熔点最高?
回答:
Tungsten is the element posing the highest melting point, 3,687 K which makes it suitable for making electrical filaments in incandescent lamps.