章节大纲

  • 常规

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  • 化学反应迹象

    A girl with curly hair shows a noticeable color change from brown to red.

    Look at the girl’s hair in the photo above. It has obviously changed color. The process in which this occurred involved . How do you know that chemical reactions have occurred? The change in color is the most obvious clue.
    ::看看上面照片中女孩的头发。 它显然改变了颜色。 发生这种情况的过程。 你怎么知道发生了化学反应? 颜色的变化是最明显的线索。

    Signs of Chemical  Reactions
    ::化学反应迹象

    A change in color is just one of several potential signs that a chemical reaction has occurred. Other potential signs include:
    ::颜色的改变只是几种潜在迹象之一,表明发生了化学反应。其他潜在迹象包括:

    • Change in .  is released or absorbed during the reaction.
      ::.的变化在反应中释放或吸收。
    • Formation  of a . Gas bubbles are released during the reaction.
      ::气体泡沫在反应中释放出来
    • Formation  of a .  A solid settles out of a solution. The solid is called a precipitate.
      ::固态的溶液 固态的溶液 固态的溶液 叫做缓冲剂

     

    Examples of Chemical Reactions
    ::化学反应实例

    Look carefully at the Figures , , and . All of the photos demonstrate chemical reactions. For each photo, identify a sign that one or more chemical reactions have taken place. 
    ::仔细查看数字 、 和 。 所有的照片都显示化学反应。 对于每张照片, 都指出发生了一种或多种化学反应的迹象 。

    A campfire with burning logs, indicating a chemical reaction through combustion.

    A burning campfire can warm you up on a cold day.
    ::烧着的营火可以在寒冷的一天温暖你

    An antacid tablet dissolving in water, creating bubbles and fizz.

    Dissolving an antacid tablet in water produces a fizzy drink.
    ::在水中分解抗酸片片可产生浓烈的饮料。

    Bowl of cottage cheese, representing a product of acid added to milk.

    Adding acid to milk produces solid curds of cottage cheese.
    ::将酸添加到牛奶中,可生产出坚固的干酪。

    Q: Did you ever make a “volcano” by pouring vinegar over a “mountain” of baking soda? If you did, you probably saw the bubble up and foam over. Did a chemical reaction occur? How do you know?
    ::问:你有没有通过将醋倒在苏打水的“山上”来制造“火山”?如果你做了,你可能会看到泡沫上升和泡沫结束。是否发生了化学反应?你怎么知道?

    A: Yes, a chemical reaction occurred. You know because the bubbles are evidence that a gas has been produced and production of a gas is a sign of a chemical reaction.
    ::A:是的,发生了化学反应。你知道,因为气泡是天然气已经生产的证据,而气体的生产是化学反应的标志。

    Summary
    ::摘要

    • Potential signs that chemical reactions have occurred include a change in color, change in temperature,  formation of a gas, and  formation of a precipitate.
      ::出现化学反应的潜在迹象包括颜色变化、温度变化、气体形成和沉淀物形成。

    Review
    ::回顾

    1. How can you tell whether a change in matter is caused by a chemical reaction?
      ::您如何判断物质变化是否是由化学反应引起的?
    2. When water freezes, it changes to ice. Is this a chemical reaction? Why or why not?
      ::当水冷时,它会变成冰。这是化学反应吗?为什么或为什么?

    Resources
    ::资源