To calculate the enthalpy change for HCL, we need to calculate the bond-breaking energy.
(H-H)=436
(CL-CL)=242
Total = 436+242 = 678Kj

Now, for bond-making…
2(H-CL)=2x431 = 862Kj

Delta H (Enthaply change) = 678 - 862 = -184Kj/mol