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    Aerial view of snow-capped mountains, likely including Mount Everest.


    Why is it harder to breathe at the top of Mount Everest than at the bottom?
    ::为什么在珠穆朗玛峰顶部呼吸比在底部呼吸更困难?

    At 29,029 feet (8,848 m), Mount Everest in the Himalayan range on the border between China and Nepal is the highest point on the earth. Its altitude presents many practical problems to climbers. The oxygen content of the air is much lower than at sea level, making it necessary to bring oxygen tanks along (although a few climbers have reached the peak without oxygen). One other problem is that of boiling water for cooking food. Although water boils at 100°C at sea level, the boiling point on top of Mount Everest is only about 70°C. This difference makes it very difficult to get a decent cup of tea (which definitely frustrated some of the British climbers). 
    ::在29,029英尺(8,848米),中国和尼泊尔边界喜马拉雅山脉的珠穆朗玛峰是地球最高点,其高度给登山者带来了许多实际问题。空气中的氧含量比海平面低得多,因此有必要将氧气罐带入水中(尽管有几位登山者没有氧气就达到了峰值 ) 。 另一个问题是烹饪食品的沸腾水问题。 尽管水在海平面100°C处沸腾,但珠穆朗玛峰顶端的沸点只有70°C左右。 这一差异使得很难买到像样的茶杯(这无疑令一些英国登山者感到沮丧 ) 。

    Boiling Point
    ::沸点

    As a is heated, the average of its particles increases. The rate of increases as more and more molecules are able to escape the liquid’s surface into the vapor phase . Eventually a point is reached when the molecules all throughout the liquid have enough kinetic energy to vaporize . At this point the liquid begins to boil. The boiling point is the temperature at which the of a liquid is equal to the external pressure .  Figure illustrates the boiling of liquid.
    ::当 a 被加热时, 其粒子的平均值会增加。 越来越多的分子能够从液体表面逃到蒸气阶段的增速。 当液体中的所有分子都有足够的动能蒸发时, 最终会达到一个点。 此时, 液体开始沸腾。 沸点是液体与外部压力相等的温度。 图显示液体的沸腾情况 。

    Comparison of evaporation and boiling in liquids, showing processes in two beakers.

    Comparison between evaporation and boiling.
    ::蒸发和沸腾之间的比较。

    In the picture on the left, the liquid is below its boiling point, yet some of the liquid evaporates. On the right, the temperature has been increased until bubbles begin to form in the body of the liquid. When the vapor pressure inside the bubble is equal to the external , the bubbles rise to the surface of liquid and burst. The temperature at which this process occurs is the boiling point of the liquid.
    ::在左边的图片中, 液体在沸点以下, 但有些液体蒸发。 在右边, 温度已经升高, 直到气泡开始在液体体内形成。 当气泡内的蒸气压力等于外部时, 气泡会升到液体表面, 并爆炸。 这一过程发生的温度是液体的沸点 。

    The normal boiling point is the temperature at which the vapor pressure of the liquid is equal to standard pressure. Because atmospheric pressure can change based on location, the boiling point of a liquid changes with the external pressure. The normal boiling point is a constant because it is defined relative to the standard atmospheric pressure of 760 mmHg (or 1 atm or 101.3 kPa).
    ::正常的沸点是液体蒸气压力与标准压力相等的温度。 由于大气压力可以随位置变化, 液体变化的沸点随外部压力变化。 正常的沸点是一个常数, 因为它与标准大气压力760毫米Hg( 或1 atm 或 101.3 kPa) 相对定义 。

    Graph showing the relationship between altitude and the boiling point of water in Fahrenheit.

    Influence of altitude on the boiling point of water.
    ::高度对沸水点的影响。

     

    CK-12 Simulation
    ::CK-12 模拟

    Ever try cooking at the top of a mountain or at sea level? Compare how atmospheric pressure, vapor pressure and boiling point relate in this simulation: 
    ::曾经尝试过在山顶或海平面做饭吗? 比较这个模拟中大气压力、蒸气压力和沸点的关联性:

    Summary
    ::摘要

    • The boiling point is the temperature at which the vapor pressure of a liquid is equal to the external pressure.
      ::沸点是液体蒸气压力等于外部压力的温度。
    • As the altitude increases, the boiling point decreases.
      ::随着高度升高 沸点会降低

    Review
    ::回顾

    1. What happens when a liquid is heated?
      ::当液体被加热时会怎样?
    2. What is the boiling point?
      ::沸点是什么?
    3. What is the pressure at which the normal boiling point is determined?
      ::确定正常沸点的压力是什么?
    4. Are the boiling point and normal boiling point always the same value, sometimes the same value, or never the same value? Explain your answer.
      ::沸点和正常沸点是否总是相同值, 有时相同值, 或者永远不相同值? 请解释您的回答 。

    Explore More
    ::探索更多

    Use the video below to answer the following questions:
    ::使用下面的视频回答下列问题:

    1. The boiling point of water is 100°C. What is an example of liquid that boils a temperature higher than the boiling point of water? 
      ::沸水点为100°C。 沸水点比沸水点高的液体是什么样的?
    2. What is an example of liquid that boiling point is below room temperature? 
      ::沸点低于室内温度的液体是什么样的?
    3. What phase change is the opposite of boiling?
      ::沸腾与什么阶段的改变相反?