Chem

emmacherry

Diamond is a crystalline form of carbon.
我想問下咩叫crystalline form.

Zend

amorphous and crystalline
crystalline = crystal般的
a regular lattice in which particles are packed orderly and in repetitive manner...

emmacherry

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?

Zend

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

emmacherry

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

Zend

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 ?

emmacherry

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 ]

Zend

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...

emmacherry

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

Zend

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.