Section outline

  • General

    Collapse all Expand all

  • 蒸汽压力曲线

    Two pots on a stove, one boiling uncovered and the other covered, producing steam.


    What is the fastest way to boil water?
    ::沸水最快的方法是什么?

    One of the first lessons in cooking is how to boil water. Yes, it sounds simple, but there are a couple of hints that speed things up. One hint is to put a lid on the pot. The picture above has water uncovered with the steam escaping to the atmosphere. If the lid is on the pot, less water will be boiled off and the water will boil faster. The buildup of pressure inside the pot helps speed up the boiling process.
    ::烹饪的第一课是如何煮水。 是的, 听起来很简单, 但有一些提示可以加快事情的速度。 其中一个提示是把锅盖盖上。 上面的图片显示, 蒸汽渗入大气后, 水会渗出。 如果锅盖在锅上, 水会少点煮, 水会更快地沸腾。 锅内的压力增加有助于加快沸腾过程 。

    Vapor Pressure Curves 
    ::蒸汽压力曲线

    The boiling points of various can be illustrated in a curve ( Figure ). A vapor pressure curve is a graph of vapor pressure as a function of temperature . To find the normal boiling point of a liquid, a horizontal line is drawn from the left at a pressure equal to standard pressure. At whatever temperature that line intersects the vapor pressure curve of a liquid is the boiling point of that liquid.
    ::各种沸点的沸点可以在曲线中显示(图 ) 。 蒸汽压力曲线是蒸汽压力的图形,视温度的函数而定。 要找到液体的正常沸点, 从左边画一条水平线, 压力等于标准压力。 无论该线在什么温度下交叉, 液体的蒸汽压力曲线就是该液体的沸点 。

    Graph showing vapor pressure curves of various liquids and their normal boiling points.

    Vapor pressure curves.
    ::蒸气压曲线

    The boiling points of liquid also correlate to the strength of the intermolecular forces . Recall that diethyl ether has weak dispersion forces, which meant that the liquid has a high vapor pressure. The weak forces also mean that it does not require a large an input of energy to make diethyl ether boil and so it has a relatively low normal boiling point of 34.6°C. Water, with its much stronger , has a low vapor pressure and a higher normal boiling point of 100°C.
    ::液体的沸点也与中间分子力量的强度相关。 回顾二乙醚的分散力较弱,这意味着液体蒸气压力高。 弱力还意味着它不需要大量能量来煮二乙醚,因此它正常的沸点相对较低,为34.6°C。 水的蒸气压力较弱,正常沸点较高,为100°C。

    As stated earlier, boiling points are affected by external pressure. At higher altitudes, the is lower. With less pressure pushing down on the surface of the liquid, it boils at a lower temperature. This can also be seen from the vapor pressure curves. If one draws a horizontal line at a lower vapor pressure, it intersects each curve at a lower temperature. The boiling point of water is 100°C at sea level, where the atmospheric pressure is standard. In Denver, Colorado at 1600 m above sea level, the atmospheric pressure is about 640 mmHg and water boils at about 95°C. On the summit of Mt. Everest the atmospheric pressure is about 255 mmHg and water boils at only 70°C. On the other hand, water boils at greater than 100°C if the external pressure is higher than standard. Pressure cookers do not allow the vapor to escape and the vapor pressure increases. Since water now boils at a temperature above 100°C, the food cooks more quickly.
    ::如前所述,沸点会受到外部压力的影响。 在高空,沸点会受到外部压力的影响。 在高空, 温度会较低。 当液体表面的压力降低时, 它会在较低的温度下沸点。 这也可以从蒸气压曲线中看出。 如果在较低的蒸气压下绘制一条水平线, 它会在较低的温度下交叉每个曲线。 在海平面, 沸水点是100°C, 大气压力是标准水平的。 在丹佛, 科罗拉多, 大气压力是640毫米Hg, 水是大约95°C。 在山顶, 大气压力是255毫米Hg, 水是仅仅在70°C。 另一方面, 如果外部压力高于标准, 水会在100°C以上。 压力炉不允许蒸气逃逸逸, 蒸气压力会增加。 由于水在100°C以上温度下沸腾, 食物煮得更快。

    A pressure cooker on a stove next to a bottle of wine.

    Pressure cooker.
    ::压力锅

    The effect of decreased air pressure can be demonstrated by placing a beaker of water in a vacuum chamber. At a low enough pressure, about 20 mmHg, water will boil at room temperature.
    ::降低空气压力的效果可以通过在真空室中放瓶装水来证明。 在足够低的压力下,大约20毫米Hg,水会在室温下沸腾。

     

     

    Summary
    ::摘要

    • A vapor pressure curve is a graph of vapor pressure as a function of temperature.
      ::蒸气压力曲线是蒸气压力的图表,视温度而定。
    • Boiling points are affected by external pressure.
      ::沸点受到外部压力的影响。

    Review
    ::回顾

    1. What does a vapor pressure curve show?
      ::蒸气压曲线显示什么?
    2. Why does diethyl ether have a low boiling point?
      ::为什么二乙醚有一个低沸点?
    3. What intermolecular forces hold water molecules together?
      ::哪些分子间联力量将水分子凝聚在一起?
    4. Why does water boil at a lower temperature when at a high altitude?
      ::为什么水在高海拔时会在低温下沸腾?

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

     

     

     

     

     

    1. What does a vacuum pump do?
      ::真空泵是做什么的?
    2. What is the role of the O-ring?
      ::O -ring的作用是什么?
    3. What happens when the vacuum pump is turned on?
      ::当真空泵开关时会怎样?
    4. What happened when the vacuum pump was turned on?
      ::当真空泵开关时发生了什么?
    5. What was the temperature of this boiling water?
      ::这沸水的温度是多少?