chem about redox reaction

係咪要every element ge oxidation number 都要有changes先可以叫做redox reaction?

唔係..只要個equation入面有一個元素oxidation number有改變就係redox reaction
拎你個example為例( ps: 你個equation寫錯左)
2Na(s)+ 2H2O(l) ---> 2NaOH(aq)+H2(g)

只有Na同H的oxidation number有改變,但O的oxidation number冇改變...
但佢仍然係redox reaction.
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我想問who ge oxidation number decrease 令到佢ge 係一個oxidizing agent?

我以copper as an example (conc.HNO3 or dilute.HNO3都得,I use dilute)
2HNO3(aq) + Cu(s) ---> Cu(NO3)2 (aq) + NO(g) + H2O(l)

Cu的oxidation number 由0 change to +2
而N的oxidation number 由+4 change to +2
N的oxidation number decrease 令到佢ge 係一個oxidizing agent

I just want to point out ==> (this is wrong)
係.只要有O.N.轉變就係redox
但係有些特別例子則不是,如organic的substitution reaction of alkane.
If we work out the oxidation number of carbon, its oxidation number changed.

係.只要有O.N.轉變就係redox
但係有些特別例子則不是,如organic的substitution reaction of alkane.

HNO3 係oxidizing agent.
咁佢同reducing agent react 就得
reducing agent有好多例子:
metal:(eg K------>K+ + e-)
halide:(eg 2Cl- -------> Cl2 + 2e-)