The polymerisation of ethylene to linear polyethylene is represented by the reaction, nCH_(2)= CH_(2) rarr (- CH_(2) - CH_(2) -) where n has a largeintegral value. Given that the average enthalpies of bond dissociation forC=C andC-C at298 K are+590 and+331kJ mol^(-1) respectively, calculate the enthalpy of polymerisation per mole of ethyleneat298 K.

The polymerisation of ethylene to linear polyethylene is represented b

1.	The polymerisation of ethylene to linear polyethylene is represented by the reaction, nCH_(2)= CH_(2) rarr (- CH_(2) - CH_(2) -) where n has a largeintegral value. Given that the average enthalpies of bond dissociation forC=C andC-C at298 K are+590 and+331kJ mol^(-1) respectively, calculate the enthalpy of polymerisation per mole of ethyleneat298 K.
Answer» Solution :In the given polymerisation reaction,ONE molecule of ETHYLENE involves breaking of C`=` C double bond and formation of threeC-C single bonds.However,in the complete polymer chain,the NUMBER of single C-C bondsformedin two per C=C double bond broken Energy required in breaking of one moleofC=C doublebonds `= 590 kJ` Energy released in the formation of two moles of`C-C` single bonds `= 2 xx 331 = 662kJ` `:.`Net energy released per moleof ethylene`= 662 - 590 = 72 kJ , i.e.,DELTAH =- 72kJmol^(-10`