F4 Chemistry Cracking

2012-05-20 2:25 am

1. Why a catalyst is needed in cracking? And why it should be hot?

2. Why alkanes are cracked in the absence of air? In my book, it said if there were air,
alkanes would burn, but what is the meaning of "burn"? And what is the problem that
the alkanes "burn"?

3. Can we use cracking to produce alkyne from alkane?

回答 (1)

[匿名]

2012-05-21 1:59 pm

✔ 最佳答案

1) cracking process need high energy and pressure ( high activation energy needed). catalyst is lower down the activation energy, causing more molecule to pass the activation energy level to start the reaction. Cracking is exothermic reaction, release energy when breaking bonds

2) the shorter the alkanes, the less intermolecular forces between neighing molecules which lead to form of gas. Burn mean being combustion reaction and form to water and CO2.

3) No because cracking can only break bonds, cannot form bonds

2012-05-21 06:02:27 補充：
3) cracking can form alkene and alkane.

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