The polymerization of propene to cyclic chain polypropane is represented by the reaction nCH3-CH=CH2→−CHCH3|−CH2−nWhere n is integral value, the average enthalpies of bond dissociation for (C=C) and (C-C) at 298 K are +590 and +3.31 kJ  mol-1  respectively. The enthalpy of polymerization is −360 kJ mol−1. Find the value of n.

Energy released = Energy due to breaking of double bond – energy due to formation of two single bonds =2× 331=662 kJ mol−1 of propene ΔH polymerization/mol=590–662                                                                                                  =−72 kJ mol−1ΔH polymerization/mol=−72 n =-360                                                    ∴n=5