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標題: Chem [打印本頁]

作者: emmacherry 時間: 20-4-2008 14:25
標題: Chem
Diamond is a crystalline form of carbon.
我想問下咩叫crystalline form.

作者: Zend 時間: 20-4-2008 16:08
amorphous and crystalline
crystalline = crystal般的
a regular lattice in which particles are packed orderly and in repetitive manner...

作者: emmacherry 時間: 20-4-2008 16:48

原帖由 Zend 於 20-4-2008 16:08 發表
amorphous and crystalline
crystalline = crystal般的
a regular lattice in which particles are packed orderly and in repetitive manner...

thanks
I want to ask also
when water is added to copper(II) sulphate,
copper (II) sulphate 係唔係變左copper(II) sulphate crystal?

作者: Zend 時間: 20-4-2008 17:08

原帖由 emmacherry 於 20-4-2008 08:48 發表

thanks
I want to ask also
when water is added to copper(II) sulphate,
copper (II) sulphate 係唔係變左copper(II) sulphate crystal?

well, it should be CuSO4(aq)...[[tk_32]]

when it is crystallized , water of crystallization of that salt is formed .
CuSO4.5H2O
when it is heated =>it finally becomes anhydrous copper(II) sulphate
CuSO4.5H2O is a blue crystal(solid form)
anhydrous CuSO4 CuSO4 is a white powder/solid

作者: emmacherry 時間: 20-4-2008 18:03

原帖由 Zend 於 20-4-2008 17:08 發表

well, it should be CuSO4(aq)...[[tk_32]]

when it is crystallized , water of crystallization of that salt is formed .
CuSO4.5H2O
when it is heated =>it finally becomes anhydrous copper(II) sulp ...

i have juz done a mc question
which states that heat would be liberated if water is added to copper(II) sulphate..
i dunno y

作者: Zend 時間: 20-4-2008 18:21

原帖由 emmacherry 於 20-4-2008 10:03 發表

i have juz done a mc question
which states that heat would be liberated if water is added to copper(II) sulphate..
i dunno y

That should be a question of "exothermic"/"endothermic" reaction ?

作者: emmacherry 時間: 20-4-2008 18:28

原帖由 Zend 於 20-4-2008 18:21 發表

That should be a question of "exothermic"/"endothermic" reaction ?

This is the question.
On heating, blue copper(II) sulphate crystals gradually change to a white powder. Which of the following statements are correct?
(1) Heat would be liberated if water is added to the white powder.
(2) On further heating, the white powder would turn reddish-brown.
(3) A chemical chagne occurs during the heating of the blue crystals.

It is obvious that (2) is wrong and (3) is correct
but i juz dun understand y (1) is correct too.
i think that the white solid left after heating is copper(II) sulphate.
and when water is added, the white solid will dissolved.
i think heat will not be evolved during the dissociation of copper(II) sulphate.

[ 本帖最後由 emmacherry 於 20-4-2008 18:29 編輯 ]

作者: Zend 時間: 20-4-2008 18:51

原帖由 emmacherry 於 20-4-2008 10:28 發表

This is the question.
On heating, blue copper(II) sulphate crystals gradually change to a white powder. Which of the following statements are correct?
(1) Heat would be liberated if water is added ...

Umm. first, simply speaking, according to conservation of energy, when u added water to anhydrous CuSO4, heat should be released.
and. (because u does supply energy to decompose it )

there is a term, although it is out-c, is called standard enthalpy change of solution

http://en.wikipedia.org/wiki/Enthalpy_change_of_solution
http://www.chemicalforums.com/index.php?topic=20358.0
from the site above, it shows that even it is dissolved to form a solution, the overall reaction is still exothermic and drawing a Born Harber Cycle...

作者: emmacherry 時間: 20-4-2008 19:15

原帖由 Zend 於 20-4-2008 18:51 發表
Umm. first, simply speaking, according to conservation of energy, when u added water to anhydrous CuSO4, heat should be released.
and. (because u does supply energy to decompose it )

there is a term, although it is out-c, is called standard enthalpy change of solution

http://en.wikipedia.org/wiki/Enthalpy_change_of_solution
http://www.chemicalforums.com/index.php?topic=20358.0
from the site above, it shows that even it is dissolved to form a solution, the overall reaction is still exothermic and drawing a Born Harber Cycle...

sry....
i dun understand the part that is bolded

作者: Zend 時間: 20-4-2008 19:22

原帖由 emmacherry 於 20-4-2008 11:15 發表

sry....
i dun understand the part that is bolded

你可以當成CuSO4.5H2O 有某個chemical energy
CuSO4 有另一個

CuSO4.5H2O->CuSO4 唔會自己發生, 要energy 去做decomposition
所以CuSO4 同佢product 的total 能量係多左

當你加番水, 做番form water of crystallization的時候
佢好自然會release 番heat.

作者: emmacherry 時間: 20-4-2008 19:26

原帖由 Zend 於 20-4-2008 19:22 發表

你可以當成CuSO4.5H2O 有某個chemical energy
CuSO4 有另一個

CuSO4.5H2O->CuSO4 唔會自己發生, 要energy 去做decomposition
所以CuSO4 同佢product 的total 能量係多左

當你加番水, 做番form water of cr ...

但係加左水
CuSO4會form water of crystallization 咩?
佢唔係會dissovle咩??

作者: Zend 時間: 20-4-2008 19:45

原帖由 emmacherry 於 20-4-2008 11:26 發表

但係加左水
CuSO4會form water of crystallization 咩?
佢唔係會dissovle咩??

以CaCl2(吸濕elephant) 為例
佢吸左水係先變water of crystallization, 過多先會溶埋成CaCl2(aq)
其實water of crystallization 只不過係water molecules 同個crystal 入面d cation, anion 有attraction ja ma.

你再加熱, 整走哂d 水就anhydrous

dissolve, 我解釋左, 即使佢係發生, 佢overall 都係exothermic

作者: octopus001 時間: 20-4-2008 19:47

原帖由 emmacherry 於 20-4-2008 11:26 發表

但係加左水
CuSO4會form water of crystallization 咩?
佢唔係會dissovle咩??

照你咁講 ...
你會點做crystallization?

作者: Zend 時間: 20-4-2008 19:49
Compound: CuSO4(s)
dH0solution/kj/mol: -66.5

Compound: CuSO4.5H2O(s)
dH0solution/kj/mol: +11.7"

如果1 mol 的CuSO4 溶係infinitely amount of water(唔好問點解, 定義)
佢會release 66.5KJ mol^-1 的能量(-ve = exothermic)
如果係個water of crystallization溶, 佢係吸+11.7 KJ mol^-1 的熱
因此, overall, 我唔理你係變CuSO4.5H2O 又好, 溶左係水變成CuSO4(aq)(真係看water 多定少)... 都係exothermic

anyway, 此等題目應該唔會係new syllabus 出現

作者: octopus001 時間: 20-4-2008 19:57

原帖由 Zend 於 20-4-2008 11:49 發表
Compound: CuSO4(s)
dH0solution/kj/mol: -66.5

Compound: CuSO4.5H2O(s)
dH0solution/kj/mol: +11.7"

如果1 mol 的CuSO4 溶係infinitely amount of water(唔好問點解, 定義)
佢會release 66.5KJ mol^-1 的 ...

我想問...
如果考果d ... 佢比d我唔識的reaction..
咁點知佢點先係exo 定 endo ....reaction?

作者: piyopiyo 時間: 20-4-2008 19:59
是否這樣...
CuSO4 . 5H2O,,,要decompose就要加熱,個hydrated salt就吸左d energy去爆個bond,,,this is an endothermic reaction [[tk_02]]
調番轉將CuSO4 變番hydrated salt要放熱[[tk_02]] by conservation of energy[[tk_21]]

作者: emmacherry 時間: 20-4-2008 20:00

原帖由 Zend 於 20-4-2008 19:49 發表
Compound: CuSO4(s)
dH0solution/kj/mol: -66.5

Compound: CuSO4.5H2O(s)
dH0solution/kj/mol: +11.7"

如果1 mol 的CuSO4 溶係infinitely amount of water(唔好問點解, 定義)
佢會release 66.5KJ mol^-1 的 ...

ok thanks
但係我最後都想問
到底我地加水落copper(II) sulphate
佢係會溶定form water of crystallization ??
因為我睇書
要form water of crystallization 係要經過一個crystallization o既程序
唔係直接dissolve 就有的

作者: Zend 時間: 20-4-2008 20:01

原帖由 octopus001 於 20-4-2008 11:57 發表

我想問...
如果考果d ... 佢比d我唔識的reaction..
咁點知佢點先係exo 定 endo ....reaction?

第一佢唔會考
第二, 放得熱主要有四類

neutralization
precipitation
combustion (usually 係, 包括用oxidizing agent 好似O2, Cl2,F2 )
Redox, 可行果d 一般直接mix 都會放熱, cell 只係將佢(chemical energy)變成electrical energy的東西..

仲有幾隻我都唔記得 XD

作者: Zend 時間: 20-4-2008 20:04

原帖由 emmacherry 於 20-4-2008 12:00 發表

ok thanks
但係我最後都想問
到底我地加水落copper(II) sulphate
佢係會溶定form water of crystallization ??
因為我睇書
要form water of crystallization 係要經過一個crystallization o既程序
唔係直接d ...

你可以這樣想, 就算佢form左solution,你加熱番佢都會出到water of crystallization
比個counter-example你

http://en.wikipedia.org/wiki/CaCl2

一般water of crystallization都係crystallization of solution出, 但我唔可以generalized 所有都係
特別係Na2CO3, MgSO4, CaCl2 這些吸水常客

作者: emmacherry 時間: 20-4-2008 20:05

原帖由 Zend 於 20-4-2008 20:01 發表

第一佢唔會考
第二, 放得熱主要有四類

neutralization
precipitation
combustion (usually 係, 包括用oxidizing agent 好似O2, Cl2,F2 )
Redox, 可行果d 一般直接mix 都會放熱, cell 只係將佢(chemical ene ...

仲有係
CuSO4+ 5H2O-----> CuSO4.5H2O
同埋
CaO + H2O----->Ca(OH)2

作者: octopus001 時間: 20-4-2008 20:06

原帖由 piyopiyo 於 20-4-2008 11:59 發表
是否這樣...
CuSO4 . 5H2O,,,要decompose就要加熱,個hydrated salt就吸左d energy去爆個bond,,,this is an endothermic reaction [[tk_02]]
調番轉將CuSO4 變番hydrated salt要放熱[[tk_02]] by conservation of ...

但係我phy果到 ..
好似nuclear fission 果課到講過...[[bao_45]]
爆bound 要energy...
但爆完bound...佢都會放energy...

[ 本帖最後由 octopus001 於 20-4-2008 12:09 編輯 ]

作者: Zend 時間: 20-4-2008 20:08

原帖由 emmacherry 於 20-4-2008 12:05 發表

仲有係
CuSO4+ 5H2O-----> CuSO4.5H2O
同埋
CaO + H2O----->Ca(OH)2

係.
但CaCl2 最特別係佢吸好多水, 連自己都溶埋- - ~

作者: Zend 時間: 20-4-2008 20:09

原帖由 octopus001 於 20-4-2008 12:06 發表

但係我phy果d ..
好似nuclear fission 果到講過...
爆bound 要energy...
但爆完bound...佢都會放energy...

nuclear fission 係mass 的"conservation of energy"
用Albert Einstein 的 Relativity, mass is a form of energy .
佢只係利用mass defect =>creat 好大的能量

作者: emmacherry 時間: 20-4-2008 20:10

原帖由 Zend 於 20-4-2008 20:08 發表

係.
但CaCl2 最特別係佢吸好多水, 連自己都溶埋- - ~

唔該晒你
真係明左好多

我想問除左conc. H2SO4 同CaCl2
仲有乜野chemical可以用黎吸水

作者: Zend 時間: 20-4-2008 20:12

原帖由 emmacherry 於 20-4-2008 12:10 發表

唔該晒你
真係明左好多

我想問除左conc. H2SO4 同CaCl2
仲有乜野chemical可以用黎吸水

P2O5, Na2SO4, MgSO4,silicon gel, conc NaOH等

係A-level (以前=.=) 係會細分佢地的用途
CaCl2 唔會用係organic substance 的drying 方面

作者: emmacherry 時間: 20-4-2008 20:14

原帖由 Zend 於 20-4-2008 20:12 發表

P2O5, Na2SO4, MgSO4,silicon gel, conc NaOH等

係A-level (以前=.=) 係會細分佢地的用途
CaCl2 唔會用係organic substance 的drying 方面

想問你對chem 攞a 有咩心得
paper 1 &2 要幾多分到

作者: Zend 時間: 20-4-2008 20:18

原帖由 emmacherry 於 20-4-2008 12:14 發表

想問你對chem 攞a 有咩心得
paper 1 &2 要幾多分到

A , 大部分人都有, 我果d 唔算係咩,...而且我其他科都唔係A
不過都係果句, 明concept, 你唔止chem A, 其實都A到
要記著每年有千四人有A, 而你有>70%的人幫你拉curve (真的, 7 萬幾考生, 得2萬8千有14分, 仲要係文理商加埋)

作者: piyopiyo 時間: 20-4-2008 20:27

原帖由 emmacherry 於 20-4-2008 20:14 發表

想問你對chem 攞a 有咩心得
paper 1 &2 要幾多分到

mc 錯 2題,LQ 90%應該差唔多 [[tk_11]]

作者: Zend 時間: 20-4-2008 20:50

原帖由 piyopiyo 於 20-4-2008 12:27 發表

mc 錯 2題,LQ 90%應該差唔多 [[tk_11]]

我好似LQ 唔夠9成, MC 錯2 題都A到 wor= =~

Physics 可能會高少少~

作者: piyopiyo 時間: 21-4-2008 09:02

原帖由 Zend 於 20-4-2008 20:18 發表

A , 大部分人都有, 我果d 唔算係咩,...而且我其他科都唔係A
不過都係果句, 明concept, 你唔止chem A, 其實都A到
要記著每年有千四人有A, 而你有>70%的人幫你拉curve (真的, 7 萬幾考生, 得2萬8千有14分, 仲要係 ...

但聽聞有5千人超過25分[[tk_02]]

作者: Zend 時間: 21-4-2008 13:40

原帖由 piyopiyo 於 21-4-2008 01:02 發表

但聽聞有5千人超過25分[[tk_02]]

4500 左右only
8千人有20 up ...

作者: piyopiyo 時間: 21-4-2008 13:56

原帖由 Zend 於 21-4-2008 13:40 發表

4500 左右only
8千人有20 up ...

4500人都好多下[[tk_02]]
如果1間學校F.1-F.7 有1000人
拎唔到25分就即係有成4,5間學校咁多ge人勁過你 [[tk_02]]
都幾恐怖

[ 本帖最後由 piyopiyo 於 21-4-2008 13:58 編輯 ]

作者: Zend 時間: 21-4-2008 16:30

原帖由 piyopiyo 於 21-4-2008 05:56 發表

4500人都好多下[[tk_02]]
如果1間學校F.1-F.7 有1000人
拎唔到25分就即係有成4,5間學校咁多ge人勁過你 [[tk_02]]
都幾恐怖

都係ga .=.=
所以你真係要考好d, 唔好學我...
不過A-level , 有大約600人會無左lor (EAS /外國讀)

所以那些BBA, PAC, Med, AC 己經唔係我可以選的野=.=
只能係餘下的Science, Engineering 到選擇x_x"

作者: piyopiyo 時間: 21-4-2008 16:49

原帖由 Zend 於 21-4-2008 16:30 發表

都係ga .=.=
所以你真係要考好d, 唔好學我...
不過A-level , 有大約600人會無左lor (EAS /外國讀)

所以那些BBA, PAC, Med, AC 己經唔係我可以選的野=.=
只能係餘下的Science, Engineering 到選擇x_x"

so 果d 得果23分入恆商果d連eng,science都無得揀咪要讀歷史[[tk_02]]
聽人說BBA無前途,點解仲咁多人揀[[tk_02]]

[ 本帖最後由 piyopiyo 於 21-4-2008 16:53 編輯 ]

作者: Zend 時間: 21-4-2008 16:55

原帖由 piyopiyo 於 21-4-2008 08:49 發表

so 果d 得果23分入恆商果d連eng,science都無得揀咪要讀歷史[[tk_02]]
聽人說BBA無前途,點解仲咁多人揀[[tk_02]]

我同你溝通唔到, 算啦...

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