MCQ
Hess's law of constant heat summation in based on
- A$E = m{c^2}$
- BConservation of mass
- ✓First law of thermodynamics
- DNone of the above
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

$A + D \rightleftharpoons AD,AD + D \rightleftharpoons A{D_2}$, $A{D_2} + D \rightleftharpoons A{D_3}$. Then equilibrium constant $'K'$ for $A + 3D \rightleftharpoons A{D_3}$ is related as

$O\left( g \right) + {e^ - } \to O_{\left( g \right)}^ - \,\,\,\,;\,\,\,\,{\Delta _f}{H^\Theta } = - 141\,kJ\,mo{l^{ - 1}}$
${O^ - }\left( g \right) + {e^ - } \to O_{\left( g \right)}^{2 - }\,\,\,\,;\,\,\,\,{\Delta _f}{H^\Theta } = + 780\,kJ\,mo{l^{ - 1}}$
Thus process of formation of $O_2^-$ in gas phase is unfavourable even thought $O_2^-$ is isoelectronic with neon. It is due to the fact that,