chem04 paper I 唔知答案點解係咁??

我諗係因為: at first slow
一開始, CaO係包住曬Ca, 令Ca唔可以接觸到水, 同唔到水react,
但係 CaO可以同水react form 左slightly soluble Ca(OH)2,
因為佢係slightly soluble, 點都會有d Ca(OH)2 溶返係水,
係哩個時候開始, Ca先可以接觸到水, react with water,
而阻住Ca react既CaO 溶得係水係因為佢可以同水react,
由於唔係reversible reaction, 佢可以react曬都得,
佢react完再form d slightly soluble 既Ca(OH)2 出黎,
所以會越黎越快...

不過, 再之後reaction應該會慢返, 因為當越黎越多既Ca(OH)2 溶左係水後, 再form出黎既Ca(OH)2已經再溶唔到係水, 哩個時候Ca(OH)2就會完全阻住Ca既reaction..(視乎有幾多水)

[問題只係問你快既時候既原因, 所以會慢返o個d係唔使講既]


點解Ca+H2O係exothermic?
當一個reaction要拆bond, 拆bond要energy, 所以個reaction就要absorb 周圍energy 黎, 令temperature 低左, 就係endothermic.

相反, 當一個reaction要make bond, 就會放energy出黎, 就係exothermic.

CaO+H2O----->Ca(OH)2 只係牽涉 make bond, 所以係exothermic reaction.


愈熱reaction愈快, 係因為reaction係發生係粒子接觸到後,
當temperature 越高, K.E of reactants 既粒子就會越大, 佢地會collide 多d, 接觸都會易d, 因此reaction 就會快d了。