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  • 化学反应

    A chemist is mixing chemicals in a lab using a pipette on a glass dish.

    Does the term chemical reaction bring to mind an image like this one? In the picture, a chemist is mixing chemicals in a lab. Many chemical reactions take place in labs. However, most chemical reactions do not. Where do they occur? They happen in the world all around you. They even happen inside your own body. In fact, you are alive only because of the many chemical reactions that constantly take place inside your cells.
    ::化学反应一词是否给人以这样的印象? 图片中, 化学家在实验室中混合化学物质。 许多化学反应在实验室中发生。 但是, 大多数化学反应不会发生。 它们在哪里发生? 它们发生在你周围的世界中。 它们甚至发生在你的身体里。 事实上, 你之所以活着, 是因为细胞里不断发生许多化学反应。

    What Is a Chemical Reaction?
    ::什么是化学反应?

    A chemical reaction is a process in which some substances change into different substances. Substances that start a chemical reaction are called reactants . Substances that are produced in the reaction are called products. can be or compounds. Chemical reactions are represented by chemical equations , like the one below, in which reactants (on the left) are connected by an arrow to products (on the right).
    ::化学反应是一种过程,在这一过程里,一些物质会变成不同的物质。开始化学反应的物质被称为反应物质。反应中产生的物质可以被称为产品。也可以被称为化合物。化学反应是由化学方程式代表的,例如下面的方程式,在这种方程式中,(左边的)反应物质通过箭头与产品(右边的)相连。

    Reactants → Products

    Chemical reactions may occur quickly or slowly. Look at the two pictures in the Figure . Both represent chemical reactions. In the picture on the left, a reaction inside a fire extinguisher causes foam to shoot out of the extinguisher. This reaction occurs almost instantly. In the picture on the right, a reaction causes the iron tool to turn to rust. This reaction occurs very slowly. In fact, it might take many years for all of the iron in the tool to turn to rust.
    ::化学反应可能很快或缓慢发生。 看看图中的两张图片。 两者代表化学反应。 在左边的图片中, 灭火器中的一种反应导致泡沫从灭火器中射出。 这种反应几乎立即发生。 在右边的图片中, 一种反应导致铁工具变成生锈。 这种反应非常缓慢。 事实上, 工具中的所有铁都可能需要许多年才能变成生锈 。

    A fire extinguisher releasing foam and a rusted screw demonstrating two types of chemical reactions.

    Q: What happens during a chemical reaction? Where do the reactants go, and where do the products come from?
    ::问题:化学反应过程中会发生什么?反应者去向何方,产品来自何方?

    A: During a chemical reaction, chemical changes take place. Some break and new chemical bonds form.
    ::A:在化学反应过程中,化学变化发生。一些断裂和新的化学结层形式。

    Same Atoms, New Bonds
    ::同一原子,新债券

    The reactants and products in a chemical reaction contain the same atoms, but they are rearranged during the reaction. As a result, the atoms are in different combinations in the products than they were in the reactants. This happens because chemical bonds break in the reactants and new chemical bonds form in the products.
    ::化学反应中的反应物和产品含有相同的原子,但在反应期间会重新排列,因此,原子在产品中的组合与在反应物中的组合不同,这是因为化学反应物中的化学结存破裂,产品中出现新的化学结存。

    Consider the chemical reaction in which water forms from oxygen and hydrogen . The Figure represents this reaction. Bonds break in molecules of hydrogen and oxygen, and then new bonds form in molecules of water. In both reactants and products there are four hydrogen atoms and two oxygen atoms, but the atoms are combined differently in water. 
    ::考虑一下氧气和氢水的化学反应。图中代表了这种反应。债券分解了氢和氧分子,然后又分解了水分子中的新的联结。在反应器和产品中,有4个氢原子和2个氧原子,但在水中,原子的组合不同。

    Chemical reaction depicting hydrogen and oxygen forming water, showing bond breaking and formation.

     

    Types of Chemical Reactions
    ::化学反应类型

    The chemical reaction in the Figure , in which water forms from hydrogen and oxygen, is an example of a . In this type of reaction, two or more reactants combine to synthesize a single product. There are several other types of chemical reactions, including decomposition, replacement, and combustion reactions. The Table compares these four types of chemical reactions.
    ::图中的化学反应,即氢和氧的水形式就是一个例子。在这种反应中,两个或两个以上的反应器合在一起合成单一产品。还有其他几种化学反应,包括分解、替换和燃烧反应。表比较了这四种化学反应。

    Type of Reaction General Equation Example
    Synthesis A+B → C 2Na + Cl 2 → 2NaCl
    Decomposition AB → A + B 2H 2 O →2H 2 + O 2
    Single Replacement A+BC → B+ AC 2K + 2H 2 O → 2KOH + H 2
    Double Replacement AB+ CD → AD + CB NaCl+ AgF → NaF + AgCl
    Combustion fuel + oxygen → carbon dioxide + water CH 4 + 2O 2 → CO 2 + 2H 2 O

    Q: The burning of wood is a chemical reaction. Which type of reaction is it?
    ::问题:木柴燃烧是一种化学反应。是哪种反应?

    A: The burning of wood—or of anything else—is a . In the combustion example in the table, the fuel is methane gas (CH 4 ).
    ::A:烧柴——或其他任何东西——是一个例子。 在表中的燃烧例子中,燃料是甲烷气(CH4)。

     

     

    Energy In and Energy Out
    ::能源投入和能源输出

    All chemical reactions involve . Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In terms of energy, there are two types of chemical reactions: endothermic reactions and .
    ::化学反应涉及所有化学反应。能源被用来打破反应器的联结,当产品出现新的联结时,能源就会释放出来。在能源方面,化学反应有两种类型:热反应和热反应。

    • In exothermic reactions, more energy is released when bonds form in products than is used to break bonds in reactants. These reactions release energy to , often in the form of or light.
      ::在异热反应中,当债券形成于产品中时,释放的能量比用来打破反应器中连接的能量要多。 这些反应释放出能量,通常以形式或光的形式,或以光的形式。
    • In endothermic reactions, more energy is used to break bonds in reactants than is released when bonds form in products. These reactions absorb energy from the environment.
      ::在局部热反应中,利用更多的能量打破反应器的联结,而不是当债券形成产品时释放出来。 这些反应吸收了来自环境的能源。

    Q: When it comes to energy, which type of reaction is the burning of wood? Is it an or an exothermic reaction? How can you tell?
    ::问题:当涉及到能源时,哪一种反应是烧柴?是热反应还是热反应?你怎么知道呢?

    A: The burning of wood is an exothermic reaction. You can tell by the heat and light energy given off by a wood fire.
    ::A:木柴的燃烧是一种过热反应。从木柴火所释放的热能和光能中可以看出。

    Summary
    ::摘要

    • A chemical reaction is a process in which some substances, called reactants, change into different substances, called products. During the reaction, chemical bonds break in the reactants and new chemical bonds form in the products.
      ::化学反应是一种过程,在这一过程中,一些物质,即所谓的反应剂,变成不同的物质,即所谓的产品,在反应过程中,化学链条断裂了反应剂,产品中出现了新的化学链条。
    • Types of chemical reactions include synthesis, decomposition, replacement, and combustion reactions.
      ::化学反应的类型包括合成、分解、替换和燃烧反应。
    • All chemical reactions involve energy. Exothermic reactions release more energy than they use. Endothermic reactions use more energy than they release.
      ::所有化学反应都涉及能量。 异热反应释放的能量比它们使用的要多。 异热反应使用能量比它们释放的能量要多。

    Review
    ::回顾

    1. What is a chemical reaction?
      ::什么是化学反应?
    2. Write a general chemical equation that shows the relationship of products to reactants in a chemical reaction.
      ::撰写一个一般化学方程式,显示产品与化学反应反应反应反应反应物之间的关系。
    3. Contrast exothermic and endothermic chemical reactions. 
      ::异热和异热化学反应。