求救!!!chemical/physical change?

咩叫chemical/physical changes???????????

我老師話:

chemical change=
1) 一樣野轉左做第2樣野，但係轉唔番做原本果樣野.(e.g. burning a wood.--->can't change back to a log)

2)果樣野既成份變左

3)果樣野轉完之後變左第2樣野，冇再有佢既成份

(但我發覺好多疑點，而已佢講既野好自相矛盾。1)同2)根本行唔通。)

e.g [1]:
Breaking a glass cup(ans = physical)
按照佢講既野:
1)一樣野轉左做第2樣野，但係轉唔番做原本果樣野:::glass cup打爛左之後根本變唔番做個glass cup(=chemical)

2)果樣野既成份變左:::冇變到,一樣都係made of glass(=physical)

3)果樣野轉完之後變左第2樣野，冇再有佢既成份:::冇轉到，都係有glass既成份(=physical)

點解Breaking a glass cup係physical change????

｛究竟我應該話佢係physical定chemical??
考試邊有咁多時間慢慢諗!?????３樣野既結果有１個唔同．．．咁點算!!!!!!!!!!!!!!??????｝

e.g[2]
Frying an egg(ans= chemical)

1)一樣野轉左做第2樣野，但係轉唔番做原本果樣野:::轉唔番喇，煎左隻蛋點變番1個蛋???(=chemical)

2)果樣野既成份變左:::冇變到,一樣都係蛋(=physical)

3)果樣野轉完之後變左第2樣野，冇再有佢既成份:::都有佢既成份wor，一樣都係蛋白同蛋黃(=physical)

點解frying an egg係chemical change!!!!!?????
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Dry ice subliming點解係chemical????
照道理佢轉states姐..
點解係chemical change?????
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A SOLID WITH A LOW MELTING PT點解係ICE???????
咁METAL算唔算???????
我唔明


求下你地幫下我!!!!!!!!!!!!!!!!!!

THX!!!!!!!