Why are bond enthalpies different for different molecules?
Jenkin writes The essential point is that the energy needed to break a particular bond depends on its molecular environment, specifically on what other bonds are present in the molecule. The thing to bear in mind is that the bond enthalpy is a measure of bond strength: the stronger the bond, the greater the value of the bond enthalpy. As an example, let us look at the C-F bond. The average bond enthalpy is quoted as 467 kJ mol-1, but in CF4 it is 485 and in CH3F 452 kJ mol-1. In CF4 there are four identical bonds; all will have the same bond enthalpy. In CH3F, the C-F bond is highly polar whilst the three C-H bonds are not. The bonding electrons are therefore drawn towards the F atom and this bond is more easily broken. In CF4 the individual bonds are, of course, also polar but are identical and their individual dipole moments add vectorially to zero. Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Ide
