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dustbus 2013-10-8 09:35 PM

catalyst

How catalyst can increase the rate of reaction without itself comsumption:smile_41:

咁姐係我有一個catalyst可以無限次使用:smile_41::smile_41:

jmlo 2013-10-9 09:22 AM

回覆 1# 的帖子

[quote] How catalyst can increase the rate of reaction without itself consumption [/quote]
The key thing that a catalyst does is to offer an alternative way in which reactants can be transformed into the desired products. Simply speaking, if a compound A is converted to a compound B through a pathway X, then when a catalyst is added, A can be converted to B through another pathway, say Y, whose activation energy is lower.

Of course, there are several working principles behind catalysis. In general, a catalyst may make certain chemical bonds of the reactants easier to be broken and certain chemical bonds of the products to be formed more readily, plus make the transition state(s) more stable.

Since catalysts only serve as substrates (or interfaces) on which chemical reactions could occur, they are not consumed, or, in other words, they do not participate genuinely in the reactions. At the end of the catalytic reactions, they are released in their original forms.

[quote] 咁姐係我有一個catalyst可以無限次使用 [/quote]
No. Either homogeneous or heterogeneous catalysts have their own lifetime, which is called turnover number. It is actually the number of cycles a catalyst molecule can function before losing its activity or even falling apart.

dustbus 2013-10-9 04:09 PM

why usually Rhodium or other transitional metal is used as catalyst:smile_41:

↗亢龍無悔↙ 2013-10-9 06:19 PM

因為佢地可以以多個oxidation state出現



[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

dustbus 2013-10-9 09:09 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-10-9 06:19 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=373352346&ptid=22534421][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
因為佢地可以以多個oxidation state出現



[img]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img] [/quote]
:funk::funk:所以唔同既oxide就可以同係唔同既reaction到用:smile_41::smile_41:

[[i] 本帖最後由 dustbus 於 2013-10-9 09:12 PM 編輯 [/i]]

↗亢龍無悔↙ 2013-10-9 10:26 PM

[quote]原帖由 [i]dustbus[/i] 於 9-10-2013 09:09 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=373362912&ptid=22534421][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]:funk::funk:所以唔同既oxide就可以同係唔同既reaction到用:smile_41::smile_41: [/quote]你學左redox 先啦:smile_04:



[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

jmlo 2013-10-9 11:44 PM

回覆 3#, 5# 的帖子

[quote] why usually Rhodium or other transitional metal is used as catalyst [/quote]
They have many accessible oxidation states. This is an important condition for a metal to be a catalyst. A catalytic process usually involves a number of electron transfer steps (i.e., redox); it is therefore necessary for the catalyst to be able to hold/release electrons readily.  

[quote] 所以唔同既oxide就可以同係唔同既reaction到用 [/quote]
Yes. Different transition metal oxides catalyze different chemical reactions (e.g. polymerization, steam reforming, hydrogenation, ...)

dustbus 2013-10-9 11:55 PM

thx for all ching:smile_40: :smile_40:
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