點知reaction係exothermic定endothermic-－航空百大

標題:

點知reaction係exothermic定endothermic?

發問:

點知reaction係exothermic定endothermic?? 可唔可以舉多dd例子解釋下點睇~

最佳解答:

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Actually , i think the best method to distinguish them is by remembering!! There are 6 cases that the reactions must be exothermic ( gives out heat): (1) All compustion reaction ((including your example C + O2 ---> CO2 )) (2) All precipitation reaction (3) All displacement reaction (4) All acid-alkali neutralization (5) Addition of a little water to an ahydrous salt (6) Reaction between calcium oxide and water There are 2 cases that the reactions must be endothermic (takes in heat) : (1) Cracking of oil fractions (2) Thermal decomposition of calcium carbonate Besides, usually near the reaction, there will be a symbol Delta H which represents heat change. If the Delta H is positive, it is an endothermic reaction. If the Delta H is negative, it is an exothermic reaction. p.s. i have answered similar question before

其他解答:

我諗你應該係cert level, 暫時你只係需要好似001咁靠記到你學咗計enthalpy changes ( delta H ) 之後就由個signs睇出嚟: delta H -VE => exothermic delta H +VE => endothermic