Section outline

  • General

    Collapse all Expand all

  • 在化学反应中保护质量

    Vibrantly colored maple leaves showing red, orange, and yellow hues in autumn.

    These vividly colored maple leaves were all bright green during the summer. Every fall, leaves of maple trees change to brilliant red, orange, and yellow colors. A change of color is a sign that a has taken place. Maple leaves change color because of .
    ::这些彩色鲜艳的红树叶在夏天都是绿色的。每秋天,红树叶都变成鲜艳的红色、橙色和黄色。颜色的改变就是发生了某种变化的标志。红树叶之所以会改变颜色,是因为 。

    Chemical Reactions and Balanced Equations
    ::化学反应和平衡等量

    A chemical reaction occurs when some substances change chemically to other substances. Chemical reactions are represented by chemical equations . Consider a simple chemical reaction, the burning of methane. In this reaction, methane (CH 4 ) combines with oxygen (O 2 ) in the air and produces carbon dioxide (CO 2 ) and water vapor (H 2 O). The reaction is represented by the following chemical equation:
    ::化学反应由化学方程式代表。 化学反应由化学方程式代表。 考虑简单的化学反应, 燃烧甲烷。 在这种反应中,甲烷(CH4)与空气中的氧(O2)结合,产生二氧化碳(CO2)和水蒸气(H2O)。 反应由以下化学方程式表示:

    CH 4 + 2O 2 → CO 2 + 2H 2 O

    This equation shows that one molecule of methane combines with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water vapor. All chemical equations must be balanced. This means that the same number of each type of must appear on both sides of the arrow.
    ::这个方程式显示一个甲烷分子与两个氧分子结合产生一个二氧化碳分子和两个水蒸气分子。 所有化学方程式必须平衡。 这意味着箭头两侧必须出现相同数量的每种类型。

    Q: Is the chemical equation for the burning of methane balanced? Count the atoms of each type on both sides of the arrow to find out.
    ::问题 : 甲烷燃烧的化学方程式是否平衡? 计算箭头两侧每种原子的原子以找出答案 。

    A: Yes, the equation is balanced. There is one carbon atom on both sides of the arrow. There are also four hydrogen atoms and four oxygen atoms on both sides of the arrow.
    ::A:是的,方程式是平衡的。箭头两侧有一个碳原子。箭头两侧还有四个氢原子和四个氧原子。

    Following the Law
    ::遵循法律

    Why must chemical equations be balanced? It’s the law! Matter cannot be created or destroyed in chemical reactions. This is the . In every chemical reaction, the same mass of matter must end up in the products as started in the reactants . Balanced chemical equations show that mass is conserved in chemical reactions.
    ::为何化学方程式必须平衡? 这是法律! 物质不能在化学反应中产生或销毁。 这就是 。 在每次化学反应中,物质质量必须像反应器中开始的那样出现在产品中。 平衡化学方程式显示质量在化学反应中得到了保护。

    Lavoisier and Conservation of Mass
    ::垃圾收集和保护

    How do scientists know that mass is always conserved in chemical reactions? Careful in the 1700s by a French chemist named Antoine Lavoisier led to this conclusion. Lavoisier carefully measured the mass of in many different chemical reactions. He carried out the reactions inside a sealed jar, like the one in the Figure . In every case, the total mass of the jar and its contents was the same after the reaction as it was before the reaction took place. This showed that matter was neither created nor destroyed in the reactions. Another outcome of Lavoisier’s research was the discovery of oxygen. 
    ::科学家如何知道质量总是在化学反应中受到保护?1700年代,一位法国化学家安托万·拉沃伊西尔小心地得出了这一结论。拉沃伊西尔仔细测量了许多不同化学反应的质量。他在一个密封的罐子里进行了反应,就像图中的罐子一样。在每一种情况下,罐子及其内装物的总质量与反应发生之前相同。这说明在反应中并没有产生或摧毁物质。拉沃伊西尔研究的另一个结果是氧气的发现。

    Portrait of Antoine Lavoisier with a glass apparatus, illustrating his experiments on mass.

    Antoine Lavoisier.
    ::安托万·拉沃耶尔

    Q: Lavoisier carried out his experiments inside a sealed glass jar. Why was sealing the jar important for his results? What might his results have been if he hadn’t sealed the jar?
    ::问:Lavoisier在密封的玻璃罐内进行了实验。 为什么密封罐子对他的结果很重要? 如果他没有封住罐子,他的结果会是什么?

    A: Sealing the jar was important so that any produced in the reactions were captured and could be measured. If he hadn’t sealed the jar, gases might have escaped detection. Then his results would have shown that there was less mass after the reactions than before. In other words, he would not have been able to conclude that mass is conserved in chemical reactions.
    ::甲:密封罐子很重要,这样就可以捕捉和测量反应中产生的任何物质。 如果他没有封住罐子,气体可能已经逃脱检测。 然后,他的检测结果就会显示反应后质量比以前少。 换句话说,他无法得出质量在化学反应中被保护的结论。

    Summary
    ::摘要

    • A chemical reaction occurs when some substances change chemically to other substances. Chemical reactions are represented by chemical equations.
      ::当某些物质以化学方式改变为其他物质时,就会发生化学反应,化学反应由化学方程式表示。
    • All chemical equations must be balanced because matter cannot be created or destroyed in chemical reactions.
      ::所有化学方程式必须平衡,因为化学反应不能产生或销毁物质。
    • Antoine Lavoisier did careful experiments to discover the law of conservation of mass in chemical reactions.
      ::安托万·拉沃伊瑟进行了认真的实验,以发现在化学反应中保护质量的法律。

    Review
    ::回顾

    1. Why must all chemical equations be balanced?
      ::为什么所有化学方程式都必须平衡?
    2. How did Lavoisier demonstrate that mass is conserved in chemical reactions?
      ::Lavoisier如何证明质量在化学反应中得到了保护?

    Explore More
    ::探索更多

    Watch the lab demonstration below , and then answer the questions that follow .
    ::看下面的实验室演示 然后回答接下来的问题

    1. What reaction is demonstrated in the video?
      ::影片中有什么反应?
    2. How can you tell that oxygen is used up in the reaction?
      ::你怎么知道氧气在反应中耗尽了?
    3. How can you tell that the product of the reaction is different from the iron that began the reaction?
      ::如何分辨反应的产物 与开始反应的铁不同?
    4. What evidence shows that mass is conserved in the reaction?
      ::哪些证据表明在反应中保留了质量?