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  • 确认化学反应

    A prepared pizza on a wooden surface topped with shredded cheese and other ingredients.

    Have you ever cooked a pizza?
    ::你做过比萨饼吗?

    Making a pizza can be as easy as buying a “take and bake” from a store and putting it in the oven to mixing up the dough and loading it up with your favorite toppings before baking it. How do you know when it is done? The most obvious sign is that the crust turns light brown. The dough is no longer flexible, but much more solid. Maybe the cheese has melted. You want the pizza to be cooked, not half-raw.
    ::做比萨饼可以像从商店里买一个“吃烤”一样容易, 放在烤箱里混合面团, 在烘烤前加上你最喜欢的面条。 你怎么知道什么时候做? 最明显的迹象是地壳变浅褐色。 面团不再灵活, 但更坚固了。 也许奶酪已经融化了。 您希望披萨被煮熟, 不是半毛的。

    Recognizing Chemical Reactions
    ::确认化学反应

    How can you tell if a is taking place? There are four visual clues that indicate that a chemical reaction is likely occurring.
    ::您如何辨别是否发生了某种反应?有四条直观线索显示可能发生了一种化学反应。

    1. A change of color occurs during the reaction.
      ::反应时会发生颜色变化 。
    2. A is produced during the reaction.
      ::A是在反应过程中产生的。
    3. A solid product called a precipitate is produced in the reaction.
      ::反应中产生一种固体产品,称为急促剂。
    4. A transfer of energy occurs as a result of the reaction.
      ::能源的转移是反应的结果。

    Mercury(II) oxide is a red solid. When it is heated to a temperature above 500°C, it easily decomposes into mercury and oxygen gas. The red color of the mercury oxide reactant becomes the silver color of mercury. The color change is the sign that the reaction is occurring.
    ::氧化汞是一种红固体。 当温度超过500°C时, 它很容易分解成汞和氧气。 氧化汞反应器的红色变成汞的银色。 颜色变化是反应发生的迹象。

    A person adding mercury(II) oxide from a jar into a test tube.
    Mercuric oxide.
    A beaker containing a shiny metallic substance, possibly mercury, illustrating a chemical reaction.
    Mercury metal.

    When zinc reacts with hydrochloric , the reaction bubbles vigorously as hydrogen gas is produced. The production of a gas is also an indication that a chemical reaction is occurring.
    ::当锌与盐酸发生反应时,随着氢气的产生,反应泡沫会非常强劲。 气体的生产也表明正在发生化学反应。

    A hand holding a test tube containing a clear solution, illustrating a chemical reaction.
    Zinc reacting with hydrochloric acid produces bubbles of hydrogen gas.

    When a colorless solution of lead(II) nitrate is added to a colorless solution of potassium iodide, a yellow solid called a precipitate is instantly produced. A precipitate is a solid product that forms from a reaction and settles out of a . The formation of a precipitate is an indication of a chemical reaction.
    ::当铅(II)硝酸盐的无色溶液添加到碘化钾的无色溶液中时,立即生产出一种被称为沉淀物的黄色固态。沉淀物是一种来自反应的固态产品,并且从一种反应中沉淀下来。加速剂的形成表明一种化学反应。

    A yellow precipitate forms in a flask during a chemical reaction.
    A yellow precipitate of solid lead(II) iodide forms immediately when solutions of lead(II) nitrate and potassium iodide are mixed.

    All chemical changes involve a transfer of energy. When zinc reacts with hydrochloric acid, the test tube becomes very warm as energy is released during the reaction. Some other reactions absorb energy. While energy changes are a potential sign of a chemical reaction, care must be taken to ensure that a chemical reaction is indeed taking place. Physical changes also involve a transfer of energy. of a solid absorbs energy, while the of a gas releases energy. The only way to be certain that a chemical reaction has taken place is to test the composition of the substances after the change has taken place to see if they are different from the starting substances.
    ::所有化学变化都涉及能量的转移。当锌与盐酸发生反应时,试验管会随着能量在反应过程中的释放而变得非常温暖。其他一些反应吸收了能量。虽然能源变化是化学反应的一种潜在迹象,但必须注意确保确实发生化学反应。物理变化还涉及固体吸收能量的转移,而气体释放能量。唯一能够确定是否发生了化学反应的方法是在变化发生后测试物质的构成,以确定它们是否与最初的物质不同。

     

     

     

     

     

     

     

    Summary
    ::摘要

    • There are four visual clues that indicate that a chemical reaction is likely occurring.
      • A change of color occurs during the reaction.
        ::反应时会发生颜色变化 。
      • A gas is produced during the reaction.
        ::反应过程中会产生气体。
      • A solid product called a precipitate is produced in the reaction.
        ::反应中产生一种固体产品,称为急促剂。
      • A transfer of energy occurs as a result of the reaction.
        ::能源的转移是反应的结果。

      ::有四种直观线索表明可能发生化学反应。 在反应过程中,颜色会发生变化。 反应过程中会产生气体。 反应过程中会产生一种固体产品,叫做沉淀剂。 反应中会发生能量转移。 反应后会发生能量转移。

    Review
    ::回顾

    1. What was the color change when mercury (II) oxide was heated?
      ::当氧化汞(II)被加热时,颜色变化是什么?
    2. What happened when zinc metal was mixed with hydrochloric acid?
      ::当锌金属与盐酸混合时发生了什么?
    3. What happens when lead nitrate and potassium iodide are mixed?
      ::当铅硝酸盐和碘化钾混杂在一起时会怎么样?