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  • 物质的物理和化学变化

    Lesson Objectives
    ::经验教训目标

    • Define and give examples of physical changes in matter.
      ::定义物质物理变化并举实例。
    • Define and give examples of chemical changes in matter.
      ::界定并举例说明物质中的化学变化。
    • State the law of conservation of mass.
      ::国家保护质量法。

    Lesson Vocabulary
    ::词汇表课程

    • chemical change
      ::化学化学变化
    • law of conservation of mass
      ::保护质量法
    • physical change
      ::物理变化

    Introduction
    ::导言

    You hit a baseball out of the park and head for first base. You're excited. The score is now tied. Your team has a chance of getting a winning home run. Then, you hear a crash. Oh no! The baseball hit a window in a neighboring house. The glass has a big hole in it, surrounded by a web of cracks (see  Figure   ). The glass has changed. It has been broken into jagged pieces. But the glass is still glass. Breaking the window is an example of a physical change in matter. It may also be bad news when the owner of the house finds out. 
    ::你从公园里打到一垒。你很兴奋。 分数现在被打定了。 你的球队有机会赢得全垒打。 然后, 你听到一个崩溃。 哦 不! 棒球击中了附近房子的窗户。 玻璃里有一个大洞, 周围是一块裂缝( 见图 ) 。 玻璃已经变了。 玻璃已经破碎成碎片。 但是玻璃还是玻璃。 打破窗户是物质变化的一个例子。 当房子主人发现时, 也可能是坏消息 。

    Physical Changes in Matter
    ::物质物理变化

    In each of these changes, only the physical properties of matter change. The chemical properties remain the same. It didn't turn into a different type of matter. Because the type of matter remains the same with physical changes, the changes are often easy to undo. For example, braided hair can be unbraided again. Melted chocolate can be put in a fridge to re-harden. Dissolving salt in water is also a physical change. How do you think you could undo it? 
    ::在这些变化中,只有物质的物理属性会变化。化学特性保持不变。它不会变成不同类型的物质。由于物质类型与物理变化相同,这些变化往往很容易消除。例如,编织的头发可以再次脱色。熔化的巧克力可以放在冰箱里重新硬化。在水中分解盐也是物理变化。你认为怎样才能解开它?

    lesson content
     
    When glass breaks, its physical properties change. Instead of one solid sheet of glass, it now has holes and cracks.

    Physical Changes in Matter
    ::物质物理变化

    A physical change in matter is a change in one or more of matter's physical properties. Glass breaking is just one example of a physical change. Some other examples are shown in  Figure   . In each example, matter may look different after the change occurs, but it's still the same. It is still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do.
    ::物质的物理变化是物质物理特性的一个或多个变化。 玻璃碎裂只是物理变化的一个例子。 图中显示了其他一些例子。 在每一个例子中, 物质在变化发生后可能不同, 但还是一样。 它仍然是同一物质, 具有相同的化学特性。 例如, 小木块可以像大木头一样燃烧。

    lesson content
     
    In each of these changes, only the physical properties of matter change. The chemical properties remain the same.

     

     

     

     

    Chemical Changes in Matter
    ::物质的化学变化

    Did you ever make a "volcano," like the one in  Figure   . It's easy, just mix baking soda with vinegar. What happens when they combine? They produce an eruption of foamy bubbles. This happens because of a chemical change. A chemical change occurs when matter changes into an entirely different substance. The new substance has different properties. When vinegar and baking soda combine, they form carbon dioxide. Carbon dioxide is a gas. It is this gas that causes the bubbles. It is the same gas that gives soft drinks their fizz.
    ::你曾经做过“火山”吗?像图中的“火山”那样。它很简单,只是把烤汽水和醋混合起来。当它们结合时会发生什么?它们会产生泡沫泡沫的喷发。它之所以发生,是因为化学变化。当物质变成完全不同的物质时,化学变化就会发生。新的物质有不同的特性。当醋和烘烤汽水结合时,它们会形成二氧化碳。二氧化碳是一种气体。正是这种气体导致了气泡。同样的气体能给它们带来软饮料。

    lesson content
     
    This girl is pouring vinegar on baking soda. This causes a bubbling "volcano."

    Not all chemical changes are as dramatic as this "volcano." Some are slower and less obvious.  Figure    and the video below show other examples of chemical changes.
    ::并非所有化学变化都和这个“火山”一样戏剧化。有些变异速度慢,不那么明显。下图和视频显示了其他化学变化的例子。

     

     

     

     

    lesson content
     
    These chemical changes all result in the formation of new substances with different chemical properties. Do you think any of these changes could be undone?

    Signs of Chemical Change
    ::化学变化迹象

    How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in  Figures    and   and in the video below.
    ::您如何判断是否发生了化学变化? 通常有线索。 数字和下面的视频中展示了几条线索。

     

     

     

     

    These chemical changes all result in the formation of new substances. These new substances have different chemical properties. Do you think any of these changes could be undone?
    ::这些化学变化都导致新物质的形成。 这些新物质具有不同的化学特性。 您认为这些变化中的任何变化都可以撤销吗 ?

    Signs of Chemical Change
    ::化学变化迹象

    How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in Figures above.
    ::您如何判断是否发生了化学变化? 通常有线索, 上面的数字中有几条。

    To decide whether a chemical change has occurred, look for these signs:
    ::为了确定是否发生了化学品变化,请寻找这些标志:

    • Gas bubbles are released. (Example: Baking soda and vinegar mix and produce bubbles.)
      ::气泡会释放出来。 (例如:烤汽水和醋混合和产生气泡。 )
    • Something changes color. (Example: Leaves turn from green to other colors.)
      ::某些东西会改变颜色 。 (例如: 叶子会从绿色转向其他颜色 。)
    • An odor is produced. (Example: Logs burn and smell smoky.)
      ::产生一种气味。 (例如:木头燃烧,闻闻烟味。 )
    • A solid comes out of a solution. (Example: Eggs cook and a white solid comes out of the clear liquid part of the egg.)
      ::固体从溶液中流出。 (例如:鸡蛋和白色固体从蛋的清液部分中流出。 )

    Reversing Chemical Changes
    ::扭转化学变化

    Chemical changes produce new substances. For this reason, they often cannot be undone. Some chemical changes can be reversed, sort of. To do so requires another chemical change to take place. For example, you can undo the tarnish on copper pennies by placing them in vinegar. The acid in the vinegar reacts with the tarnish. This is a chemical change that makes the pennies bright and shiny again. You can try this yourself at home to see how well it works. Other chemical changes cannot be reversed at all or may be difficult to do. Rusting is a chemical change. If metal rusts, the best you can do is to sand off the rust to get down to the shiny metal. Although the metal may now be shiny, the rust was removed. The rust was not changed back into the original metal.  
    ::化学变化产生新的物质。 基于这个原因, 它们往往无法撤销。 有些化学变化可以倒转, 有点可以倒转 。 这样做需要进行另一种化学变化。 例如, 您可以通过将铜小便放在醋中来消除铜小便上的污点。 醋中的酸会与污点发生反应 。 这是一个化学变化, 使便便便再次亮亮和闪亮。 您可以在家中尝试这个变化, 看看它是如何工作的 。 其他化学变化是完全无法倒转的, 或者可能很难做到的 。 其他化学变化是化学变化。 腐蚀是一种化学变化。 如果金属生锈, 你所能做的就是把生锈的沙子丢到闪亮的金属上。 尽管金属现在可能发光, 锈迹已被除去 。 锈迹并没有被重新变成原始金属 。

    Some chemical reactions occur in only one direction. These reactions are called irreversible reactions. For example, you cannot change a fried egg back into a raw egg. Can you think of some other irreversible reactions related to cooking? Would you like a piece of cake? To make a cake you mix items such as such as eggs and flour. They are mixed together and baked to form the cake. The cake can’t be “unbaked” and “unmixed.”  So making a cake is irreversible change. Therefore, baking is a form of chemical change. 
    ::某些化学反应只出现一个方向。 这些反应被称为不可逆反应。 比如, 您不能将煎蛋变回生鸡蛋。 您能想到一些与烹饪相关的不可逆反应吗? 您想要一块蛋糕吗? 您想要做蛋糕吗? 将蛋和面粉等物品混合成一个蛋糕。 它们混合在一起,烤成蛋糕。 蛋糕不能“ 不烤”和“不混合 ” 。 因此蛋糕是不可逆的改变。 因此,烘烤是一种化学变化的形式。

    Baking a cake is an irreversible reaction

     

    How Temperature Affects Changes in Matter
    ::温度影响如何变化物质

    Have you are burned something on the stove or in the oven? Do you know why things burn? It all has to do with temperature. Changes in matter are affected by temperature. For example, what if you place a cake in the oven and you leave it in too long? What do you think will happen? That's right, it will probably burn. The same thing will happen if the oven setting is too high and you apply too much heat. In either case, heat has affected the rate of change in matter. It's probably obvious that when the temperature is increased a chemical change, like cooking, will occur faster. What about a physical change? Are physical changes affected by temperature? 
    ::炉子上还是烤箱里有烧焦的东西? 你知道烧焦的原因吗? 它都与温度有关。 物质的变化会受到温度的影响。 比如, 如果你在烤箱里放一个蛋糕, 留下的时间会太长呢? 你认为会发生什么? 是的, 它可能会燃烧。 同样的事情也会发生, 如果烤箱设置太高, 你施用过多的热。 无论哪种情况, 热都会影响物质变化的速度。 很明显, 当温度升高时, 化学变化, 比如烹饪, 会更快发生。 关于物理变化呢? 物理变化会受到温度的影响吗?

    Most of us have seen steam rising off a wet road after a summer rainstorm. This happens because the road surface is very warm. The warm road and warm air temperature causes the water to evaporate quickly. The liquid water is turning into water vapor, but it is still water. The evaporation of water is a physical change.  So yes, temperature affects the rate that physical change occurs.
    ::我们大多数人都看到夏季暴风雨后潮湿的公路上的蒸汽在上升。 这是因为公路表面非常温暖。 温暖的公路和温暖的空气温度导致水迅速蒸发。 液态水正在变成水蒸发,但它仍然是水。 水的蒸发是一种物理变化。 因此,温度会影响物理变化发生的速度。

    Are there other examples you can think of? What about how fast something melts? Have you ever left a candy bar outside in the sun? Just like how temperature increases the rate a substance dissolves, temperature affects the rate of change in many other ways. As temperature increases, changes in matter happen more quickly. For example, do you think an ice cube will melt faster in warm temperatures? Of course they will, which is why we keep ice in the freezer. If not, they would melt and eventually evaporate. When temperatures are lower, change happens more slowly. Think about your refrigerator. What happens if you leave the door open? Items in the refrigerator may thaw, but they may also spoil more quickly. 
    ::你还能想到其他例子吗?关于什么东西融化的速度如何?你有没有把糖果棒留在太阳外面?就像温度如何提高物质溶解的速度一样,温度会以其他方式影响变化速度。随着温度的上升,物质的变化会更快发生。例如,你认为冰块会在温暖的温度下更快地融化?当然,这就是为什么我们在冷冻室中保留冰块的原因。如果不是,它们会融化并最终蒸发。当温度降低时,变化会更缓慢。想想冰箱会怎样?如果你把门打开,会怎样?冰箱里的东西会融化得更快,但它们也会破坏得更快。

    We use refrigerators to slow down the natural rate of change in the foods we eat. Food left out can spoil quickly. That is why it is really important to keep foods cool. The next time your mother tells you to close the refrigerator door, don't just do it because she told you so. Do it because you know a lot about physics and rates of change of matter. 
    ::我们用冰箱来减慢我们吃的食物的自然变化速度。 食物被漏掉会很快变质。 这就是为什么保持食物冷却非常重要。 下次你妈妈叫你关冰箱门的时候, 不要因为她告诉你了就这么做。 这样做是因为你知道很多物理和物质变化率。

    Conservation of Mass
    ::保护质量

    If you build a campfire, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all that is left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way. What do you think happened? The truth is that the same amount of matter still exists. The wood changed not only to ashes, but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Although matter was changed, it was not created or destroyed. Because the same amount of matter still exists, we can say that matter is conserved. You may wonder how it can be conserved if something is now missing?
    ::如果你建造了一座营火,你就从一大堆木柴和木头开始。当火烧焦的时候,堆积逐渐缩小。到了傍晚,只剩下一小堆灰烬。当你们从火堆开始的时候,发生了什么事情呢?它被火焰摧毁了吗?它看起来是这样吗?你以为事情是这样吗?事实是这样的:同样数量的事情仍然存在。木柴不仅变成灰烬,还变成二氧化碳、水蒸气和其他气体。气体漂浮在空气中,留下的只是灰烬。虽然物质已经改变,但没有创造或摧毁。由于同样数量的事情仍然存在,我们可以说物质是保存的。你不知道如果现在缺少什么东西,它会如何保存呢?

    lesson content
     
    Burning is a chemical process. Is mass destroyed when wood burns?

    Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with.
    ::假设你在烧木头之前已经测量了木头的质量。假设你把烧木头释放的气体封住,然后测量其质量和骨灰的质量。你会发现什么?灰烬和气体加在一起,其质量与最初的木头相同。

    This example illustrates the  law of conservation of mass.  The law states that matter cannot be created or destroyed. Even when matter goes through physical or chemical changes, the total mass of matter always remains the same. 
    ::这个例子说明了保护质量的法律,法律规定不能创造或销毁物质,即使物质经过物理或化学变化,物质的总质量始终保持不变。

    Lesson Summary
    ::经验教训摘要

    • Physical changes are changes in the physical properties of matter. They do not affect the makeup of matter. An example of a physical change is glass breaking.
      ::物理变化是指物质物理特性的变化,不影响物质的构成。物理变化的一个例子是玻璃碎裂。
    • Chemical changes are changes in the makeup and chemical properties of matter. An example of a chemical change is wood burning.
      ::化学变化是指物质构成和化学特性的变化,化学变化的一个例子是木材燃烧。
    • Matter cannot be created or destroyed even when it changes. This is the law of conservation of mass.
      ::物质即使改变也不能创造或销毁。这是保护质量法则。

    Lesson Review Questions
    ::经验回顾问题

    Recall
    ::回顾

    1. What is a physical change in matter?
      ::什么是物质上的改变?
    1. What happens during a chemical change in matter?
      ::化学物质变化时会发生什么?
    1. State the law of conservation of mass.
      ::国家保护质量法。

    Apply Concepts
    ::应用概念

    1. When a plant grows, its mass increases over time. Does this mean that new matter is created? Why or why not?
      ::当植物生长的时候,其质量会随时间而增加。这是否意味着新物质会被创造出来?为什么或为什么没有呢?
    1. Butter melts when you heat it in a pan on the stove. Is this a chemical change or a physical change? How can you tell?
      ::黄油在炉子上加热时会融化。 这是化学变化还是物理变化? 你怎么知道?
    1. Is popping popcorn a physical or chemical change? How can you tell?
      ::爆米花是物理变化还是化学变化?

    Think Critically
    ::仔细仔细思考

    1. Compare and contrast physical and chemical changes in matter. Give an example of each type of change.
      ::比较和对比物质的物理变化和化学变化。请举例说明每一种变化。

    Points to Consider
    ::需要考虑的要点

    Some physical changes in matter are changes of state.
    ::物质的某些物理变化是状态的变化。

    • What are the states of matter?
      ::事态如何?
    • What might cause matter to change state?
      ::是什么原因导致改变状态?