Standard molar enthalpies of formation of $ {CaCO_{3(s)} CaO_{(s)}}$ and $ {CO_{2(g)}}$ are $ {-1206.92\, kJ \, mol^{-1}, -635.09\, kJ\, mol^{-1}}$ and $ {-393.51\, kJ\, mol^{-1}}$ respectively. The $\Delta H_r$ for decomposition of $ {CaCO_{3(s)}}$ is