章节大纲

  • A hot spring emitting steam, showing boiling water and surrounding rocky terrain.

    Why is steam rising from the spring in this picture? It’s because the water is boiling hot. The bubbles in the water show that it is boiling. The water in the spring is hot enough to boil because it comes from an underground source near hot molten rock.
    ::这张照片中为什么蒸汽从泉水中涌出? 这是因为水是沸腾的。 水中的泡沫显示它是沸腾的。 泉水足够热,足以沸腾,因为它来自靠近热熔岩的地下来源。

    All Steamed Up
    ::全部蒸汽起来

    Steam actually consists of tiny droplets of water. What you can’t see in the picture is the water vapor that is also present in the air above the spring. Water vapor is water in the gaseous state. It constantly rises up from the surface of boiling hot water. Why? At high temperatures, particles of a liquid gain enough to completely overcome the force of attraction between them, so they change to a . The gas forms bubbles that rise to the surface of the liquid because gas is less dense than liquid. The bubbling up of the liquid is called boiling. When the bubbles reach the surface, the gas escapes into the air. The entire process in which a liquid boils and changes to a gas that escapes into the air is called vaporization . 
    ::蒸气实际上由微小的水滴组成。 在图片中,你看不到的水蒸气也存在于春天上空的空气中。 水蒸气是气体状态中的水。 它不断从沸腾的热水表面上升。 为什么? 在高温下, 液体的微粒足以完全克服它们之间的吸引力, 从而变成一个。 气泡会形成气泡, 因为气体密度小于液体而升至液体表面。 液体的泡泡被称作沸腾。 当气泡到达地表时, 气体会渗入空气中。 液体沸腾和改变气体进入空气的整个过程被称为蒸气化过程。

    Q: Why does steam form over the hot spring pictured above?
    ::问:为什么上面的温泉里 蒸汽会形成?

    A: Steam forms when some of the water vapor from the boiling water cools in the air and condenses to form droplets of liquid water.
    ::A:当沸水中的某些水蒸气在空气中冷却,凝结成液态水滴时,蒸气形成蒸气。

    Vaporization vs. Evaporation
    ::蒸发与蒸发

    Vaporization is easily confused with , but the two processes are not the same. Evaporation also changes a liquid to a gas, but it doesn’t involve boiling. Instead, evaporation occurs when particles at the surface of a liquid gain enough energy to escape into the air. This happens without the liquid becoming hot enough to boil.
    ::蒸发很容易与蒸发混为一谈,但这两种过程并不一样。 蒸发也会将液体变成气体,但并不涉及沸腾。 相反,当液体表面的颗粒获得足够的能量逃入空气时,就会发生蒸发。 发生这种情况时,液体不会变得热到可以沸腾的地步。

     

     

    Boiling Point
    ::沸点

    The at which a substance boils and changes to a gas is called its boiling point. Boiling point is a physical property of matter. The boiling point of pure water is 100°C. Other substances may have higher or lower boiling points. Several examples are listed in the Table . Pure water is included in the table for comparison.
    ::物质沸腾和气体变化时称为沸点。沸点是物质的物理属性。纯水的沸点为100°C。其他物质可能具有更高或更低的沸点。表格中列出了几个例子。表格中列出了纯水,供比较。

    Substance Boiling Point (°C)
    Hydrogen -253
    Nitrogen -196
    Carbon dioxide -79
    Ammonia -36
    Pure water 100
    Salty ocean water 101
    Petroleum 210
    Olive oil 300
    Sodium chloride 1413

    Q: Assume you want to get the salt (sodium chloride) out of salt water. Based on information in the table, how could you do it?
    ::问题:假设你想将盐(氯化钠)从盐水中取出。根据表格中的信息,你如何做到这一点?

    A: You could the salt water to 101°C. The water would boil and vaporize but the salt would not. Instead, the salt would be left behind as particles.
    ::A:你可以将盐水降到101°C。水会沸腾和蒸发,但盐不会。相反,盐会作为颗粒留在后面。

    Q: Oxygen is a gas at room temperature (20°C). What does this tell you about its boiling point?
    ::问题:氧是室温(20°C)下的一种气体。这告诉您它的沸点是什么?

    A: The boiling point of oxygen must be lower than 20°C. Otherwise, it would be a liquid at room temperature.
    ::A: 氧的沸点必须低于20°C。 否则,它就是室温下的液体。

    Summary
    ::摘要

    • Vaporization is the process in which a liquid boils and changes to a gas.
      ::蒸发是液体沸腾和气体改变的过程。
    • Vaporization is easily confused with evaporation, but evaporation doesn’t involve boiling.
      ::蒸发很容易与蒸发混为一谈,
    • The temperature at which a liquid boils and starts changing to a gas is called its boiling point. The boiling point of pure water is 100°C.
      ::液体沸腾并开始变成气体的温度被称为沸点。 净水的沸点为100°C。

    Review
    ::回顾

    1. What is vaporization?
      ::什么是蒸发?
    2. Outline how vaporization occurs.
      ::外观是如何蒸发的 。
    3. Make a table comparing and contrasting vaporization and evaporation.
      ::做一个比较和对比蒸发和蒸发的表格。
    4. Define boiling point. What is the boiling point of pure water?
      ::确定沸点。清水的沸点是什么?
    5. Suppose you place an aluminum pot containing water over the flame on a stovetop. Before long, the water starts boiling and turning to water vapor. The pot becomes very hot but otherwise appears to be unchanged by the increase in temperature. Based on these observations, what can you conclude about the boiling point of aluminum?
      ::假设你把含水的铝锅放在火炉顶上。不久,水就开始沸腾,变成水蒸气。锅变得非常热,但温度上升时似乎没有变化。根据这些观察,你对铝的沸点能得出什么结论?

    Resources
    ::资源