✔ 最佳答案
yeah, they're chemical reactions. the products are different from the reactants -- new substances are formed.
for example, anhydrous CuSO4 is colorless, has density of 3.6g/cm^3, and can be heated to 650 degree before decomposition.
however, the pentahydrate is blue, has density of 2.3g/cm^3, and decompose at 110 degree.
the two species have different properties (especially chemical properties), so they're different compounds.
the reaction converts a substance into another new substance, so it's chemical reaction.
2011-01-01 04:15:54 補充:
... 唉, 說到那個層面的話, 就很難把反應分類的了...
問題像雞與雞蛋:
水合物是否新的物質?
如果水合的過程算是化學反應, 那水合物就是新的物質; 如果水合物是新的物質, 那水合的過程就算是化學反應.
我的看法是, 算化學反應, 因為兩者間最少有一個分別: 無水化合物能與水作水合反應, 而水合物則不會與水作水合反應.
離子/分子間的鏈結方式確是有本質上的改變;
以copper(II) sulphate 為例, 銅離子本來是被硫酸根離子包圍, 水合後改由水分子包圍.
很令人頭痛耶... 不過要考慮到這些的話, 其實是不是化學反應, 本身也不太重要了. (笑
2011-01-06 22:19:42 補充:
i'd say, Neither.
first, water molecules are NOT decomposed. they just escape from the crystal.
second, is that simple vaporization? i don't think so.
vaporization refers to change of state of free substance...
2011-01-06 22:24:51 補充:
對了, 我想起很重要的事!!
這些水合物的化學式是恆定的, 原子比例是恆定的,
即CuSO4 定會且只會有5個水 (且不論其他少見的水合物), 不會多也不會少.
如果水合作用是物理變化, 沒有新物質形成, 那即是造成混合物 ---- 而混合物的各物質比例是隨意的, 是不會有恆定的化學式或原子數比!
既然現在有恆定的化學式, 意味著不是物理過程生成的混合物,
而是由化學反應生成的"化合物" !!