Polymerisation of ethene to poly - ethene is represented by the equation
n(CH2=CH2)→(−CH2−CH2−)n
Given that average enthalpies of C = C and C - C bonds at 298 K are 590 and 331 kJ mol−1 respectively, predict the enthalpy change when 56g of ethene changes to polyethylene.
-144 kJ
In the polymerisation of CH2=CH2 into (−CH2−CH2−)n, one C = C double bond is changed into 2C - C bonds.
Hence, ΔH=ΔHC=C−2ΔHC−C=590−2×331
=−72 kJ mol−1
Number of moles of C2H4 polymerised =5628=2
Enthalpy change =2×(−72)=−144kJ