There are two kinds of changes—chemical change and physical change.

In a chemical change, there is always a new substance(物質(zhì)) formed. Breaking up water into hydrogen(氫氣) and oxygen(氧氣) is a chemical change. In each of the chemical change at least one new substance is formed. A change is not a chemical change if it doesn’t form a new substance.

Physical changes are very common, too. There are many examples. You can make a physical change by tearing(撕開)a piece of paper in two, or by cutting a piece of iron with lathe(車床). Here paper is still paper, and the iron is still iron.

Another way of making physical change is dissolving(融化) something in water. When you dissolve salt in water, the salt disappears. You may think that a new substance has been formed. But really there is no new substance. The salt is still salt. You can still taste it. So the dissolving of anything is a physical change.

When water freezes, the change is also a physical one. The water changes from liquid(液體) to solid(固體). But it is still the same substance. That is why the freezing of anything is a physical change.

1．It is not ______ if a new substance is not formed in the change.

A．a(chǎn) physical change                  B．a(chǎn) chemical change

C．change of state(狀態(tài))            D．a(chǎn) change

2．The dissolving of salt in water is _________.

A．a(chǎn) physical change                  B．a(chǎn) chemical change

C．hydrogen and oxygen             D．breaking up

3．Which is wrong according to the passage?

A．A new substance is always formed in a physical change.

B．Two kinds of changes are talked about in this passage.

C．If a change forms a new substance, it’s a chemical change.

D．The physical changes include the freezing of anything.

練習(xí)冊系列答案
相關(guān)習(xí)題

科目：初中英語 來源： 題型：


The taxis in this city ________ in the same color. You can see them everywhere.

A. are  B. has  C. is  D. have

查看答案和解析>>

科目：初中英語 來源： 題型：


.  The door is not ______ for the elephant to pass.

     A. wide enough    B. widely enough    C. enough wide   D. enough widely

查看答案和解析>>

科目：初中英語 來源： 題型：


— Shall I tell Tina about it?

— No, you_________. I’ve told her.

A．won’t              B．mustn’t            C．didn’t have to          D．needn’t

查看答案和解析>>

科目：初中英語 來源： 題型：


— John, could you come and help me in the kitchen, please?

— Sorry, Mum. I_________ Tom search for information on the net.

A．help              B．helped                 C．have helped        D．a(chǎn)m helping

查看答案和解析>>

科目：初中英語 來源： 題型：


補全對話

Son: Hey, Dad?

Dad: What’s the matter?

Son: 1．_________________________________

Dad: What movie are you going to see?

Son: The Palace. It’s really an interesting movie.

Dad: OK. 2．_______________________________

Son: I am going to see the movie with Tony.

Dad: 3．______________________________.

Son: I’ll come back at 9 o’clock. The movie is a little long.

Dad: Don’t stay out late. You must get back home before 9:30.

Son: All right. 4．__________________________

Dad: No, I need it. And you are too young to drive a car. But 5．__________________________

Son: It’s kind of you to do that. Thank you, Dad.

查看答案和解析>>

科目：初中英語 來源： 題型：


My friend Jack is from _____European country.We all think he is____

honest boy.

        A. a, a       B. a, an         C. an, an       D. an, a

查看答案和解析>>

科目：初中英語 來源： 題型：


Many people go to school for education. School education is very important and useful, but no one can learn everything from school. A teacher, no matter how much he knows, can't teach his student everything. His work is to show his students how to learn .He teaches them how to read and how to think. So much more is to be learned outside school by students themselves.

successful. They invented so many things. The reason for their success is that they knew how to study. They read many books outside school. They worked hard all their lives, wasting not a single moment. The most important thing is that they know how to use their brains（大腦）.

(  )1. Students can’t learn everything in school because _____________.

A.     the teacher doesn’t know much

B.     the teacher can only teach them how to read and write

C.     the teacher would not like to teach

D.     there are still many things for the students to learn outside

(  )2.A teacher’s work is _________________

A.     to teach all subjects                       B. to teach everything

C. to teach the students how to read and think     D. to work hard

(  )3.To know how to____is much more important than facts or formulas by heart.

A.     work out maths problems          B. remember all the facts

C. study science                    D. studyx k  b  1 .c o  m

(  )4.Why did the famous scientists become successful ? Because__________

A.     they knew how to study

B.     they remembered all the formulas

C.     they didn’t get everything from school

D.     they didn’t know how to use their brains

(  )5.Which is WRONG according  to the passage?

A.     Outside school study is as important as school study

B.     It’s more important to know how to learn than only remember some facts

 and formulas.

C.     It’s very easy to use a formula in working out a maths problem.

D.     It’s helpful to read more books outside school.

查看答案和解析>>

科目：初中英語 來源： 題型：


 Battery-operated slippers are used ______ seeing in the dark.

A. to              B. as              C. by             D. for

查看答案和解析>>

同步練習(xí)冊答案