有關放熱反應的問題

Question

我想請問有咩因素決定一個化學反應是否放熱反應?

Answer 1

Exothermic refers to a transformation in which a system releases heat to the surroundings:

Q < 0
When the transformation occurs at constant pressure:

∆H < 0
and constant volume:

∆U < 0
In an adiabatic system (i.e. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.


Some examples of exothermic processes are:

Freezing of water
Combustion
Respiration

In a thermochemical reaction that is exothermic, the heat is placed as a product on the product's side (heat is a product of the reaction).

Answer 2

其實冇咩rule好講...
organic/simple molecular 既話可以睇bonding既強度:
拆bond要energy, 造bond放energy;
好似N2 + O2 ------> 2NO
要拆強既N三N 同 O=O, 改造兩個弱既N=O,
咪要吸熱LOR...
但係其他就冇咩好講,
一般記住: 燃燒/中和/沉澱都係放熱.