古时候煤炭炉只能达到1200℃左右，因为孙悟空是石猴，其主要成分是二氧化硅(Silicondioxide)，熔点（melting point-Physical property）在1650℃左右，不溶于水也不溶于酸，但溶于氢氟酸，能和熔融碱类起作用。所以温度达不到，的确炼不掉！所以懂点chemistry多么重要！

原来石猴的组成没那么简单，它不仅只含有Silicon dioxide，还有含有碳酸钙(Calcium carbonate)，在八卦炉里煅烧，Calcium carbonate发生thermal decomposition反应：CaCO3 ⇌ CaO+CO2。Carbon dioxide使得八卦炉气压增大，最终导致爆炸，孙悟空就可以趁机逃出！破炉而出之后变得狂暴，这是因为他身上的Calcium carbonate变成了氧化钙(calcium oxide)，吸收空气中的水分发生放热(exothermic)反应，以致N多年不能冷静。

后来孙悟空跟唐僧一起去西天取经怎么变得温和了呢？原来如来把孙悟空压在五行山下，五百年的日晒雨淋，孙悟空身上的calcium oxide又吸收了雨水，随后变成了氢氧化钙（calciumhydroxide），所以性情也就变的温和了。在西行的路上，孙悟空身上的calcium hydroxide又在不断的吸收Carbondioxide，最终到了西天之后又变成了Calcium carbonate，又变成了坚硬的石身。看来这一切都和一个thermal decomposition反应有关啊！Thermal decomposition (thermolysis)  is  a chemical decomposition (breakdown) caused by heat. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. 

现在来说点正事，AS常考的几个反应机理：

(1) Electrophilic substitution反应机理

In electrophilic substitutionin aromatic compounds, an atom appended tothe aromatic ring, usually hydrogen, is replaced byan electrophile. The most important reactions of this type that take placeare aromatic nitration, aromatic halogenation, aromatic sulfonation and acylation and alkylating Friedel-Crafts reactions. It further consists of alkylation and acylation.

例如：苯的溴代反应，其中Br+作亲电试剂，苯作为富电子中心

(2) nucleophilic substitution反应机理

Nucleophilic substitution is a fundamental class of reactions in which an electronrich nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms to replace a leaving group; the positive or partially positive atom is referred to as an electrophile.The whole molecular entity of which the electrophile and the leaving group arepart is usually called the substrate.

例如：halogenalkane的水解反应中，OH-作为亲核试剂，碳正离子作为缺电子中心，根据溶剂和反应物分为SN1和SN2。

其中旧键（C-Br）的断裂和新键(C-OH)的生成同时发生,整个取代反应速率同时与OH-浓度和halogenalkane的浓度成正比。

SN1：

分两步完成，整个反应速率由慢反应步骤决定，故只与halogenalkane的浓度有关。

(3) electrophilic addition反应机理

实质： in a chemical compound, a π bond is broken and two new σ bonds are formed. The substrate of an electrophilic addition reaction must have a double bond or triple bond.

The driving force for this reaction is the formation of an electrophile X+ that forms a covalent bond with an electron-rich unsaturated C=C bond. The positive chargeon X is transferred to the carbon-carbon bond, forming a carbocation during the formation of the C-X bond.

主要有：卤素加成反应、加卤化氢反应、水合反应、氢化反应、羟汞化反应、硼氢化-氧化反应、Prins反应，以及与硫酸、次卤酸、有机酸、醇和酚的加成反应；

例如alkene的 electrophilic addition反应：

(4) nucleophilic addition反应机理

实质：a nucleophilic addition reaction is an addition reaction where a chemical compound with an electron-deficient or electrophilic double or triple bond,a π bond, reacts with electron-rich reactant, termed a nucleophile,with disappearance of the double bond and creation of two new single,or σ bonds. The reactions are involved in the biological synthesis of compounds in the metabolism of every living organism,and are used by chemists in academia and industries such as pharmaceuticals to prepare most newcomplex organic chemicals, and so are central toorganic chemistry. Addition reactions require the presence of groups with multiplebonds in the electrophile: carbon–hetero atom multiple bonds as in carbonyls, imines, and nitriles, or carbon–carbon double or triple bonds.

例如：

(5) freeradical substitution反应机理

In organic chemistry, a radical-substitution reaction is a substitution reaction involving free radicals as a reactive intermediate.In the first step called initiationa free radical iscreated by homolysis. Homolysis can be brought about byheat or ultraviolet light but also by radical initiators such as organic peroxides or azo compounds.UV Light is used to create two free radicals from one diatomic species. The final step is called termination in which the radical recombines with another radical species. If the reaction is not terminated, but instead the radical group(s) goon to react further, the steps where new radicals are formed and then react is collectively known as propagation because a new radical is created available for secondary reactions.

主要有：烷烃紫外线条件下与halogen发生取代反应、CFC与臭氧分子反应。

以烷烃在紫外线照射下与halogen的反应为例：

第一步（共价键断裂产生自由基是Initiation stage）:

第二步：引发阶段（Initiation stage）产生的自由基与反应体系中的分子作用，产生一个新的分子和一个新的自由基，新产生的自由基再与体系中的分子作用又产生一个新的分子和一个新的自由基，如此周而复始、反复进行的反应过程称为链（式）反应，如下图：