蒸发
在炎热的夏天,你有没有把湿衣服擦干?你知道水从布上去哪里了吗?那么,由于太阳,水被转化为水蒸气,这被称为蒸发。因此,蒸发是指物质的液态变为气态(蒸汽)的过程。此外,蒸发需要热量。
什么是蒸发?
蒸发是在热量存在下将液态物质转化为气态物质的过程。许多人对蒸发和沸腾感到困惑,因为在沸腾中,液体也会变成气态。但是,有一个区别,首先是液体在特定温度下发生沸腾,而蒸发可以在低于沸点的任何温度下发生。沸腾也是一种整体现象,而蒸发是一种表面现象,这意味着蒸发只能发生在液体的表面。在蒸发过程中,具有较高动能的分子仅从液体的最顶层消散。蒸发还有一个独特的特性,即蒸发会产生冷却效果。夏天用来储存凉水的土锅,因为水从锅的小孔中渗出,导致蒸发,导致锅内的水变凉。沙漠冷却器也根据蒸发原理工作。
蒸发也取决于一些因素,如温度、液体表面积、风速和湿度。我们将在本文中详细讨论这一点。
蒸发的例子
蒸发的例子有很多,但这里我们只讨论其中的几个:
- 在阳光下晒干衣服:我们都在阳光下晒干了我们的衣服,湿衣服因为蒸发而变干,水变成水蒸气。
- 水体干涸:我们看到在夏季,池塘和湖泊中的水会因蒸发而减少或有时干涸。
- 水循环:这是蒸发的一个很好的例子,在上面两个中我们讨论了蒸发如何将水变成水蒸气。这种水蒸气进一步上升到天空并凝结成云,然后沉淀下来。因此,蒸发对于调节水循环非常重要。
- 盐的形成:自然或工业盐的形成是由于蒸发,水被蒸发留下盐。
- 拖地的干燥
- 夏季沙漠冷却器的工作。
影响蒸发的因素
到目前为止,我们讨论了什么是蒸发以及它对我们有何用处。蒸发在许多方面使我们的生活变得轻松,甚至它也有助于水循环。但是蒸发取决于一些将控制蒸发速率的因素。还有一点需要注意的是蒸发是一个缓慢的过程,但有一些外部因素会增加或减慢蒸发速度。让我们讨论所有这些蒸发因素:
温度
第一个因素是温度,因为我们知道蒸发可以在沸点之前的任何温度下发生,但温度对蒸发也有影响。它会决定蒸发的速度,温度越高蒸发的速度就越快。现在的问题是如何?我们都知道温度会增加动能,作为用来破坏结合液体分子的分子间作用力的能量。因此,当我们施加更多温度时,分子会迅速破坏其分子间作用力并蒸发。
所以我们可以写:
Temperature ∝ Evaporation
例:我们都见过在炎热的夏天衣服比平时干得快。这是由于温度因素。
液体的表面积
前面我们已经讨论过,蒸发是一种表面现象,而表面对蒸发的速度有一定的影响。表面积越大,蒸发速率越大。因此,如果有更多的表面积,那么更多的液体分子将出现在表面上,这意味着更多的分子会破坏它们的分子间键,这将增加蒸发速率。所以我们可以把它写成;
Surface area of liquid ∝ Evaporation
示例:与浅杯中的水相比,盘子中的水蒸发得更快,这是因为盘子比浅杯提供了更大的液体表面积。
湿度
湿度是指空气中的湿度或水蒸气量。我们会说空气中的水蒸气越多就是湿度。随着湿度的增加,蒸发速率会降低。
Humidity ∝ 1/Evaporation
示例:在雨季,我们的周围比我们的衣服更潮湿,很难把我们的衣服擦干。
风速
风速与蒸发量成正比,意味着随着风速的增加,蒸发量也会增加。
Wind Speed ∝ Evaporation
示例:在刮风的日子里,衣服比正常日子更快地干燥。这是因为风降低了湿度,从而增加了蒸发率。
示例问题
问题 1:用一个例子来定义蒸发。
回答:
Evaporation is a process where the liquid state of matter converted into a gaseous state of matter in the presence of heat.
For example, We all dried up our clothes in the sun, the wet clothes get dries up because of evaporation where the water turns into water vapour.
问题二:为什么在潮湿的季节衣服很难晾干?
回答:
Since we know that humidity refers to the amount of wetness or water vapour in the air. The more water vapour in the air we will say more is humidity. With more humidity the rate of evaporation gets decrease Thus, it will become very hard to dry up the clothes in the humid season.
问题 3:写出四个蒸发的例子。
回答:
Examples of evaporation are as follows:
1. Drying of water bodies: We have seen in summer water in the ponds and lake get decrease or sometimes dried up due to evaporation.
2. Water cycle: This is a very good example of evaporation, in the above two we discussed how evaporation turns water into water vapour this water vapour further go to the sky and get condensed to form a cloud, and later it got precipitated. So, evaporation is very important to regulate the water cycle.
3. Salt formation: Naturally or industrially salt form due to evaporation where the water gets evaporated to leave us salt.
4. Drying of a Mopped Floor
问题 4:温度升高如何影响蒸发速率?
回答:
Since we know evaporation can happen at any temperature before the boiling point, but the temperature has a role in evaporation too. It will determine the rate of evaporation, the more the temperature more is the rate of evaporation. Now the question is how? We all know that the temperature will increase the kinetic energy, and the energy used to break intermolecular forces that bind the liquid molecule. So, when we apply more temperature the molecule fastly break their intermolecular forces and fastly get evaporated.
问题 5:写出任何 3 个影响蒸发的因素。
回答:
Following are some factors that determine the rate of evaporation:
1. Surface area of the liquid: More is a surface area more will be the rate of evaporation. Thus, the Surface area of liquid ∝ Evaporation. For example, the same amount of water gets evaporated quickly in a plate than the water in a shallow cup, this is because the plate offers a greater surface area for the liquid than the shallow cup.
2. Humidity: With more humidity, the rate of evaporation gets decrease, means Humidity ∝ 1/Evaporation. For example in the rainy season when our surrounding is more humid than it is very difficult to dry up our clothes.
3. Wind Speed: Wind speed is directly proportional to evaporation means with the increase of wind speed there would be an increase in the rate of evaporation, which means Wind Speed ∝ Evaporation. For example, on a windy day, clothes get quickly dried up than the normal days. This is because the wind decreased the humidity which will increase the rate of evaporation.