bond dissociation enthalpy

katie

2008-02-14 6:20 am

The defination of bond dissociation enthalpy is that when one mole of a particular bond is broken in a particular envirionment under standard conditions.

CH4(g) -> CH3(g) + H(g)

1.H2O(g) -> OH(g) + H(g)
2.H2O(l) -> OH(g) + H(g)

Q1.咁如係under standard conditions的話, 咁1. and 2. 邊條式先啱?
Q2. 咁點解OH 係 in gases state?

回答 (1)

Uncle Michael

2008-02-14 7:41 am

✔ 最佳答案

Bond dissociation enthalpy is the energy needed to break one mole of specific covalent bonds of a specific substance in gaseous state.

Q2.
In the definition, the specific substance must be in gaseous state. This is because there are no interactions (attractions and repulsions) between molecules of idea gases, and thus all enthalpy changes are due to the breaking of the specific covalent bonds.

Q1.
According to the definition of bond dissociation enthalpy, equation 1 is correct.
For equation 2, the enthalpy change is due to the breaking of O-H bonds in water and the breaking hydrogen bonds between H2O molecules.

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