章节大纲

  • lesson content

    Is It Magic?
    ::是魔法吗?

    This innocuous-looking bottle contains a greenish-yellow, poisonous gas. The gas is chlorine, which is also used as bleach and to keep the in pools and hot tubs free of germs. Chlorine can kill just about anything. Would you breathe in chlorine gas or drink liquid chlorine? Of course not, but you often eat a compound containing chlorine. You probably eat this chlorine compound just about every day. Can you guess what it is? It's table salt.
    ::这个无端的瓶子含有一种绿色的黄黄色有毒气体。 气体是氯, 也被用作漂白剂, 用来保持水池和热水池中没有细菌。 氯可以杀死任何东西。 您会呼吸氯气还是喝液态氯? 当然不会, 但你经常吃含有氯的化合物。 您大概每天都会吃氯化合物。 您猜它是什么? 它是桌盐 。

    lesson content

    Salt in a shaker is sodium chloride.
    ::搅拌器中的盐是氯化钠

    Table salt is actually sodium chloride (NaCl), which forms when chlorine and sodium (Na) combine in certain proportions. How does the toxic green chemical chlorine change into the harmless white compound we know as table salt? It isn't magic — it's chemistry, and it happens in a chemical reaction .
    ::食盐其实是氯化钠(NaCl),当氯和钠(Na)以一定比例结合时,它就形成了氯化钠(NaCl)。有毒的绿色化学氯如何变成我们称之为食盐的无害的白色化合物?它不是魔法,而是化学,它发生在化学反应中。

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

    A chemical reaction is a process that changes some chemical substances into others. A substance that starts a chemical reaction is called a reactant , and a substance that forms as a result of a chemical reaction is called a product. During the reaction, the reactants  are used up to create the products.
    ::化学反应是一种将某些化学物质改变为其他化学物质的过程。 开始化学反应的物质被称为反应剂,因化学反应而形成的物质被称为产品。 在反应过程中,反应剂被用来制造产品。

    The burning of methane gas, as shown in the picture , is a  chemical reaction. In this reaction, the reactants are methane (CH 4 ) and oxygen (O 2 ), and the products are carbon dioxide (CO 2 ) and water (H 2 O). As this example shows, a chemical reaction involves the breaking and forming of chemical bonds , which are forces that hold together the atoms of a molecule. When methane burns, for example, bonds break within the methane and oxygen molecules, and new bonds form in the molecules of carbon dioxide and water. 
    ::如图所示,甲烷气体的燃烧是一种化学反应,在这种反应中,反应物是甲烷(CH4)和氧(O2),产品是二氧化碳(CO2)和水(H2O),如本例子所示,化学反应是化学联系的破碎和形成,化学联系是将分子原子聚集在一起的力量。例如,甲烷燃烧时,甲烷和氧分子内部的联结破裂,二氧化碳和水分子中的新联结形式。

    lesson content

    Flames from methane burning
    ::甲烷燃烧产生的火焰

    Chemical Equations
    ::化学等量

    Chemical reactions can be represented by chemical equations . A chemical equation is a symbolic way of showing what happens during a chemical reaction. The burning of methane, for example, can be represented by the chemical equation:
    ::化学反应可以用化学方程式表示。化学方程式是显示化学反应期间发生情况的象征性方式。例如,甲烷的燃烧可以用化学方程式表示:

    CH 4 + 2O 2 → CO 2 + 2H 2 O
    ::CH4 + 2O2 + 2O2 + CO2 + 2H2O

    The arrow in a chemical equation separates the reactants from the products, and shows the direction in which the reaction proceeds. If the reaction could occur in the opposite direction as well, two arrows pointing in opposite directions would be used. The number 2 in front of O 2 and H 2 O, called the coefficient, shows that two oxygen molecules and two water molecules are involved in the reaction. If just one molecule is involved, no number is placed in front of the chemical symbol.  N ote the subscript of 2 for the oxygen (O) and hydrogen (H) atoms in the oxygen and water molecules, respectively. That tells you that each oxygen molecule is made up of two oxygen atoms. If there is no subscript, then there is a single atom . Thus, one water molecule is made up of two hydrogen atoms and one oxygen atom. In order for th is chemical reaction to take place, one methane molecule reacts with two oxygen molecules to form one carbon dioxide molecule and two water molecules.
    ::化学方程式中的箭头将反应器与产品分离, 并显示反应过程的方向。 如果反应也可能发生在相反的方向上, 就会使用两支反方向的箭头。 在O2和H2O前面的数字2, 称为系数, 显示反应涉及两个氧分子和两个水分子。 如果只涉及一个分子, 化学符号前面没有数字。 注意氧( O) 和氢( H) 原子在氧和水分子中的下标值。 说明每个氧分子由两个氧原子组成。 如果没有下标, 那么就有一个单一原子。 因此, 一个水分子由两个氢原子和一个氧原子组成。 为了发生这种化学反应, 一个甲烷分子与两个氧分子发生反应, 形成一个二氧化碳分子和两个水分子。

    Conservation of Mass
    ::保护质量

    In a chemical reaction, the quantity of each element does not change. There is the same amount of each element in the products as there was in the reactants. Mass is always conserved. According to the law of of mass —   which was first demonstrated convincingly by Fre nch chemist Antoine Lavoisier in 1785 — mass is neither created nor destroyed during a chemical reaction. Therefore, during a chemical reaction, the total mass of products is equal to the total mass of reactants.  The conservation of mass is reflected in a reaction's chemical equation. The same number of atoms of each element appears on each side of the arrow. In the chemical equation above, there are four hydrogen atoms on each side of the arrow. Can you find all four of them on each side of the equation?
    ::在化学反应中,每个元素的数量没有变化。产品中的每个元素的数量与反应器中的每个元素相同。质量总是受到保护的。根据质量法则(法国化学家安托万·拉沃伊瑟于1785年首次令人信服地证明这一点),质量在化学反应中既没有产生,也没有销毁。因此,在化学反应中,产品的总质量与反应器的总质量相等。质量的保护反映在反应的化学方程式中。每个元素的原子数量都出现在箭头的两侧。在以上化学方程式中,箭头的两侧都有四个氢原子。您能否在方程式的两侧找到所有四个氢原子?

    Chemical vs. Physical Changes
    ::化学与物理变化

    Many processes that happen all around us on a daily basis involve chemical reactions. Not every change, however, is a chemical change. Some changes are simply physical and do not involve chemical reactions. If you break an eggshell and pour out the egg into a pan, its chemical makeup and properties do not change. This is just a physical change. No chemical reactions have occurred, and no chemical bonds have broken or formed. Other examples of physical changes are cutting paper into smaller pieces and letting an ice cube melt.
    ::每天发生在我们周围的许多过程都涉及化学反应。 然而,并非所有变化都是化学变化。 有些变化只是物理变化,并不涉及化学反应。 如果您打破蛋壳,把蛋倒入锅里, 其化学构成和特性不会改变。 这只是物理变化而已。 没有发生化学反应, 也没有化学联系破裂或形成。 其他物理变化的例子是将纸切成小块, 让冰块融化。

    What if you put the egg in the pan over a hot flame? The egg turns to a rubbery solid and changes color. The properties of the egg have changed because its chemical makeup has changed. Cooking the egg is a chemical change that involves chemical reactions. Other common examples of chemical changes include a cake baking, metal rusting, and a candle burning. Another example is pictured .
    ::如果把鸡蛋放在锅里放在热火上呢? 鸡蛋变成橡皮固态并改变颜色。 蛋的特性已经改变, 因为它的化学化妆已经改变。 煮鸡蛋是一种化学变化, 涉及化学反应。 化学变化的其他常见例子包括蛋糕烘烤、 金属生锈和蜡烛燃烧。 另一个例子是图片显示的 。

    lesson content

    Rotting oranges are an example of the decomposition of organic matter, which involves chemical reactions.
    ::旋转橙是有机物分解的一个例子,有机物的分解涉及化学反应。

    Summary
    ::摘要

    • A chemical reaction is a process that changes some chemical substances into others. A substance that starts a chemical reaction is called a reactant, and a substance that forms during  a chemical reaction is called a product. During the chemical reaction, bonds break in reactants and new bonds form in products.
      ::化学反应是一种将某些化学物质改变为其他化学物质的过程。 开始化学反应的物质被称为反应剂,在化学反应中形成的一种物质被称为产品。 在化学反应中,债券断裂反应器和产品中的新债券形式。
    • Chemical reactions can be represented by chemical equations. According to the law of conservation of mass, mass is always conserved in a chemical reaction, so a chemical equation must be balanced, with the same number of atoms of each type of element in the products as in the reactants.
      ::化学反应可以用化学方程式来表示。 根据质量保护法,质量总是在化学反应中加以保护,因此化学方程式必须平衡,产品中每种元素的原子数量与反应物中的原子数量相同。
    • Many chemical reactions — such as iron rusting and organic matter rotting — occur all around us each day, but not all changes are chemical processes. Some changes — like  ice melting or paper being torn into smaller pieces — are physical processes that do not involve chemical reactions and the formation of new substances. 
      ::许多化学反应——例如铁锈和有机物腐烂——每天都发生在我们周围,但并非所有变化都是化学过程,有些变化——如冰融化或纸张被撕成小块——是物理过程,不涉及化学反应和新物质的形成。

    Review
    ::回顾

    1. What is a chemical reaction?
    ::1. 什么是化学反应?

    2. Define the  reactants and products in a chemical reaction.
    ::2. 界定化学反应中的反应物和产品。

    3. List three examples of common changes that involve chemical reactions.
    ::3. 列举三个涉及化学反应的常见变化的例子。

    4. Define a chemical bond.
    ::4. 界定化学品联结。

    5. What is a chemical equation? Give an example.
    ::5. 什么是化学方程式?举一个例子。

    6. What does it mean for a chemical equation to be balanced ? Why must a chemical equation be balanced?
    ::6. 化学方程式平衡意味着什么?为什么化学方程式必须平衡?

    7. Our cells use glucose (C 6 H 12 O 6 ) to obtain energy in a chemical reaction called cellular respiration. In this reaction, six oxygen molecules (O 2 ) react with one glucose molecule. Answer the following questions about this reaction:
    ::7. 我们的细胞利用葡萄糖(C6H12O6)获得一种称为细胞呼吸的化学反应的能量。在这一反应中,六个氧分子(O2)与一个葡萄糖分子发生反应。

    a. How many oxygen atoms are in one molecule of glucose?
    ::a. 葡萄糖分子中有多少氧原子?

    b. Write out what the reactant side of this equation would look like.
    ::b. 写出这个等式的反动面是什么样子。

    c. In total, how many oxygen atoms are in the reactants? Explain how you calculated your answer.
    ::c. 反应器中总共有多少氧原子?解释你是如何计算答案的。

    d. In total, how many oxygen atoms are in the products? Is it possible to answer this question without knowing what the products are? Why or why not?
    :伤心d) 产品中总共有多少氧原子?能否回答这个问题而不知道产品是什么?为什么或为什么不是?

     

    8. Answer the following questions about the following equation:  CH 4  + 2O 2  → CO 2  + 2H 2 O
    ::8. 回答下列关于下列公式的问题:CH4+2O2 +2O2 +2H2O

    a. Can carbon dioxide (CO 2 ) transform  into methane (CH 4 ) and oxygen (O 2 ) in this reaction? Why or why not?
    ::a. 在这种反应中,二氧化碳(CO2)能否转化成甲烷(CH4)和氧(O2)?

    b. How many molecules of carbon dioxide (CO 2 ) are produced in this reaction?
    ::b. 在这一反应中产生多少二氧化碳(CO2)分子?

     

    9. Is the evaporation of liquid water into water vapor a chemical reaction? Why or why not?
    ::9. 液态水蒸发到水蒸气中的化学反应是否是一种化学反应?为什么或为什么不是?

     

    10. Why do bonds break in the reactants during  a chemical reaction?
    ::10. 在化学反应期间,为什么债券会断裂反应器?

    Explore More
    ::探索更多

    To learn more about the conservation of mass and how it affects chemical reactions, watch the video below. 
    ::要了解更多关于质量保护及其如何影响化学反应的知识,请观看下面的录像。

     The video below discusses the difference between physical and chemical changes. 
    ::以下影片讨论物理变化与化学变化之间的区别。