首页
登录
职称英语
"Physical and Chemical Properties and Changes" → Sugar, water
"Physical and Chemical Properties and Changes" → Sugar, water
游客
2024-01-04
28
管理
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 [br] The word unique in the passage is closest in meaning to
选项
A、distinctive
B、idealized
C、primary
D、significant
答案
A
解析
In this passage, distinctive is a synonym for "unique."
转载请注明原文地址:https://tihaiku.com/zcyy/3334226.html
相关试题推荐
ChooseTWOletters,A-E.WhatTWOchangeswillbemadetothecompetitionnexty
Choosethecorrectanswer,A,BorC.[br]Whatchangecausedchangesincrocodi
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactiv
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactiv
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactiv
Choosethecorrectletter,A,BorC.TrafficChangesinGranford[br]According
ChooseTWOlettersA-E.WhichTWOchangestotheorganisationofthisyear’sfes
ChooseTWOlettersA-E.WhichTWOchangestotheorganisationofthisyear’sfes
ChooseTWOlettersA-E.WhichTWOchangestotheorganisationofthisyear’sfes
ChooseTWOlettersA-E.WhichTWOchangestotheorganisationofthisyear’sfes
随机试题
TheBritishoriginatedordevelopedthemodernformsandrulesofanumberofsp
Thehumannoseisanunderratedtool.Humansareoftenthoughttobeinsensi
MemoTo:AllEmployeesFrom:BerryE.Silver,PresidentDate:Oc
下列影响广告受众授传因素的有()。A.制约时间、必须时间、闲暇时间的分配 B
下列对天癸认识的叙述,错误的是A.天癸之源在肾 B.随肾气的盛衰而变化 C.
下列叙述正确的是A.梅毒螺旋体具有内毒素B.梅毒螺旋体抵抗力强C.梅毒螺旋体属于
Thechangeinthatvillagewasmiraculou
新生儿生理性体重下降是指平均比出生时下降了A.2% B.3%~9% C.10
110kV及以上电压等级的过程层SV网络、过程层GOOSE网络、站控层MMS网络
孕妇感染梅毒的治疗,首选( )。A.甲硝唑 B.第三代头孢菌素 C.青霉素
最新回复
(
0
)