首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
"Physical and Chemical Properties and Changes" → Sugar, water, and aluminum are different substances. Each substance has spe
"Physical and Chemical Properties and Changes" → Sugar, water, and aluminum are different substances. Each substance has spe
admin
2012-01-14
63
问题
"Physical and Chemical Properties and Changes"
→ Sugar, water, and aluminum are different substances. Each substance has specific properties that do not depend on the quantity of the substance. Properties that can be used to identify or characterize a substance—and distinguish that substance from other substances--are called characteristic properties. They are subdivided into two categories: physical properties and chemical properties.
The characteristic physical properties of a substance are those that identify the substance without causing a change in the composition of the substance. They do not depend on the quantity of substance.A Color, odor, density, melting point, boiling point, hardness, metallic luster or shininess, ductility, malleability, and viscosity are all characteristic physical properties. For exam pie, aluminum is a metal that is both ductile and malleable.B Another example of a physical property is water. Whether a small pan of water is raised to its boiling point or a very large kettle of water is raised to its boiling point, the tem- perature at which the water boils is the same value, 100 degrees C or 212 degrees F.C Similarly, the freezing point of water is 0 degrees C or 32 degrees F. These values are independent of quantity. D
Characteristic properties that relate to changes in the composition of a substance or to how it reacts with other substances are called chemical properties. The following questions
pertain
to the chemical properties of a substance.
1. Does it burn in air?
2. Does it decompose (break up into smaller substances) when heated?
3. What happens when it is placed in an acid?
4. What other chemicals will it react with, and what substances are obtained from the reaction?
Characteristic physical and chemical properties—also called intensive properties—are used to identify a substance. In addition to the characteristic physical properties already mentioned, some intensive physical properties include the tendency to dissolve in water, electrical conductivity, and density,
which
is the ratio of mass to volume.
Additional intensive chemical properties include the tendency of a sub stance to react with another substance, to tarnish, to corrode, to explode, or to act as a poison or carcinogen (cancer-causing agent).
Extensive properties of substances are those that depend on the quantity of the sample, including measurements of mass, volume, and length.
Whereas intensive:properties help identify or characterize a particular kind of matter, extensive properties relate to the amount present.
If a lump of candle wax is cut or broken into smaller pieces, or if it is melted (a change of state), the sample remaining is still candle wax. When cooled, the molten wax returns to a solid. In these examples, only a physical change has taken place; that is, the composition of the substance was not affected.
→ When a candle is burned, there are both physical and chemical changes. After the candle is lighted, the solid wax near the burning wick melts. This is a physical change; the composition of the wax does not change as it goes from solid to liquid. Some of the wax is drawn into the burning wick where a chemical change occurs. Here, wax in the candle flame reacts chemically with oxygen in the air to form carbon dioxide gas and water vapor. In any chemical change, one or more substances are used up while one or more new substances are formed. The new substances produced have their own
unique
physical and chemical properties.
The apparent disappearance of something, like the candle wax, however, is not necessarily a sign that we are observing a chemical change. For example, when water evaporates from a glass and disappears, it has changed from a liquid to a gas (called water vapor), but in both forms it is water. This is a phase change (liquid to gas), which is a physical change. When attempting to determine whether a change is physical or chemical, one should ask the
Critical
question: Has the fundamental composition of the substance changed? In a chemical change (a reaction), it has, but in a physical change, it has not.
Glossary
ductility: can be drawn into wire
malleability: can be shaped
viscosity: thick, resistant to flow
Look at the four squares [■] that show where the following sentence could be inserted in the passage. It can be made into wire or thin, flexible sheets. Where could the sentence best be added? Click on a square [■] to insert the sentence in the passage.
选项
A、Square A.
B、Square B.
C、Square C.
D、Square D.
答案
B
解析
Pronoun reference is a transitional device that connects the insert sentence with the previous sentence. The pronoun "It" in the insert sentence refers to "aluminum" in the previous sentence. The description of aluminum as "ductile" and "malleable" in the previous sentence means that this metal can be made into wire or shaped into flexible sheets as stated in the insert sentence.
转载请注明原文地址:https://kaotiyun.com/show/PQyO777K
0
托福(TOEFL)
相关试题推荐
DothefollowingstatementsagreewiththeinformationgiveninReadingPassage1?Inboxes5-8onyouranswersheetwriteTRUE
BIRDMIGRATIONABirdshavemanyuniquedesignfeaturesthatenablethemtoperformsuchamazingfeatsofendurance.Theyareeq
BIRDMIGRATIONABirdshavemanyuniquedesignfeaturesthatenablethemtoperformsuchamazingfeatsofendurance.Theyareeq
LivingDunesWhenyouthinkofasanddune,youprobablypictureabarrenpileoflifelesssand.Butsanddunesareactuallydyn
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
AccordingtoMrSingh,onwhichthingdomanypeoplemakesuperficialobservations?MrSinghbelievesthatthebestwaytobes
Thievesoftentargetstudents’homesbecausestudents______.Theinsurancecompanyhasa24______.
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.SperrinHalls
WriteNOMORETHANTWOWORDSforeachanswer.BeWellOnlineProgramme=interactivewebsitewithresourcestohelpreach
WriteNOMORETHANTWOWORDSforeachanswer.BeWellOnlineProgramme=interactivewebsitewithresourcestohelpreach
随机试题
对于微分电路,当输入为矩形波时,在电阻端取得输出的波形为()波。
关于顺磁性对比剂的概念,错误的是
某乡政府为发展本地经济,便作出一项决定,要求本乡所有居民每户种植芦笋五亩,凡不按规定种植芦笋者,每亩罚款300元,罚款并入本乡芦笋基金,并强制种植,如有抗拒者,则由芦笋执法大队予以拘留15日以下处罚。该乡居民王某因拒绝执行该决定,而被迫当场交纳罚款1500
处理工程质量事故的依据有()。
“四大菜系”中以昧型多样、变化巧妙而著称的是()。
南水北调工程通过三条调水线路与()的联系,以利于实现中国水资源南北调配、东西互济的合理配置格局。
公安政策对调整有关国家安全和社会治安秩序的社会关系具有重要意义,体现在()
下列关于联营的说法中,正确的是()。
Johnturnedadeafeartohismother’ssuggestion,______heknewittobevaluable.
A、Sherecommendedanewstyle.B、Sheofferedsomegifttotheman.C、Sheapologizedtothemanoncemore.D、Shecheckedallthe
最新回复
(
0
)