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
29
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
The word critical in the passage is closest in meaning to
选项
A、last
B、important
C、difficult
D、simple
答案
B
解析
In this passage, important is a synonym for"critical."
转载请注明原文地址:https://kaotiyun.com/show/xQyO777K
0
托福(TOEFL)
相关试题推荐
Completeeachsentencewiththecorrectending,A-I,below.Writethecorrectletter,A-I,inboxes18-22onyouranswersheet.
DothefollowingstatementsagreewiththeinformationgiveninReadingPassage1?Inboxes5-8onyouranswersheetwriteTRUE
AccidentalScientistsAAparadoxliesclosetotheheartofscientificdiscovery.Ifyouknowjustwhatyouarelookingfor,fi
TheStudyofChimpanzeeCultureA.Afterstudyingthesimilaritiesbetweenchimpanzeesandhumansforyears,researchershav
Theprofessorsaysthatsuperhighways______.【29】
Atenancyagreementisa______betweenthetenantandthelandlord.Tenantsshouldkeepa______ofthetenancyagreement.
WhatisthepurposeofJaneandRick’smeetingwiththetutor?
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
A、She’swritingresearchpapersB、She’sworkingonaconservationprojectC、She’sstudyingforexamsD、She’sdoingherbiologyh
随机试题
某市环保局应当地居民的举报对排放烟尘超标的某化工厂作出了处罚5万元的行政处罚,并责令其限期整改。化工厂对环保局的行政处罚决定不服,向法院提起诉讼。诉讼期间,原告找到被告要求协商解决,被告同意,遂变更了原来的处罚决定,对原告只加收两倍的排污费。原告向法院申请
神经递质的信息传递方式A.突触分泌B.旁分泌C.内分泌D.自分泌E.外分泌
企业的加权平均资本成本指的是
甲公司2015年发现2013年有笔实际资产损失10万元在当年未扣除,已知甲公司2013年应纳税所得额为8万元,2014年应纳税所得额为3万元,2015年应纳税所得额为12万元,甲公司将上述损失在2015年进行资产损失申报,该公司2015年实际应缴纳的企业所
现有关系表:学生(宿舍编号,宿舍地址,学号,姓名,性别,专业,出生日期),它的主键是()。
不仅人上了年纪会难以集中注意力,就连蜘蛛也有类似的情况。年轻蜘蛛结的网整齐均匀,角度完美;年老蜘蛛结的网可能出现缺口,形状怪异。蜘蛛越老,结的网就越没有章法。科学家由此认为,随着时间的流逝,这种动物的大脑也会像人脑一样退化。以下哪项如果为真,最能质疑科学家
Inmostcultures,whenyoumeetacquaintancesforthefirsttimeduringaday,itisnormaltogreetthem.Themainpurposeoft
WhatdidHelenrecentlypass?
Somefindingsareissuedrecentlyaboutattendingacommunitycollege.Mostworkerswhohavea【C1】______fromacommunitycollege
A--trafficregulationB--guidepostC--trafficlightD--trafficpoliceE--safet
最新回复
(
0
)