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 specif
"Physical and Chemical Properties and Changes" Sugar, water, and aluminum are different substances. Each substance has specif
admin
2018-07-24
33
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 the substance. A Color, odor, density, melting point, boiling point, hardness, metallic luster or shininess,
ductility
,
malleability
, and
viscosity
are all characteristic physical properties. For example, 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 temperature 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 degree 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 substance 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/H3fO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.HowtokillbadinsectsChemicalmethodsThesesolutions
Completethesentencesbelow.WriteNOMORETHANTWOWORDSforeachanswer.Thedreamtimecanbeexperiencedbeneaththe______
Completethesentencesbelow.WriteONEWORDAND/ORANUMBERforeachanswer.Atthebeginningofthereport,thehypothesisan
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrom
Completethenotesbelow.WriteONEWORDONLYforeachanswer.DevelopmentStudiesDevelopmentStudiesattemptstounderstand-
077876345提示句为“…mayIhaveyourcontactnumberthatwecanusetoreachyouduringtheweek?”,当这一句出现之后就应该通过这个问题预测到接下来回答者的回答内容,当提示
A、Therightsofprivatebusinessownersshouldbeprotected.B、Thegovernmentshouldn’tinterfereinprivatebusiness.C、Politic
PatentsandInventionsWhenaninventionismade,theinventorhasthreepossiblecoursesofactionopentohim:first,hec
PatentsandInventionsWhenaninventionismade,theinventorhasthreepossiblecoursesofactionopentohim:first,hec
"ConquestbyPatents"→Patentsareaformofintellectualpropertyrightsoftentoutedasameanstogive’incentiveandrew
随机试题
小倩回想起上次期末考试没考好所体验的挫败感,这种记忆属于()
我国从()开始实行的申论考试科目,既考察了应试者多方面的知识,又考察了应试者的文字表达、分析与解决问题的能力、创新能力和思维的深度。
吸入性肺脓肿的致病菌多为厌氧菌,治疗时应首选
衡量组织兴奋性高低的指标是
根据我国法律规定,关于法人,下列哪一表述是正确的?(2010年卷三4题,单选)
(2005年)已知点作直线运动,其运动方程为x=12一t3(x以cm计,t以s计)。则点在前3s内走过的路程为()cm。
按目前规定,资产评估明细表样表包括以下几个层次()。
与对纸质出版物编辑人员的要求相比,对电子出版物编辑。人员的独特要求有()等。
一个年级所有五个平行班级的数学平均成绩分别为60,62,62,68,70,那么整个年级的数学平均分为()。
Takingthenation-stateasourpointofspatialreference,wecandifferentiatenotonlybetweenhistoriographiesonasu
最新回复
(
0
)