The $H_2O_{(g)}$ molecule dissociates as:
$(i)$ $H_2O_{(g)} \to H_{(g)} + OH_{(g)}; \Delta H = 490 \ kJ$
$(ii)$ $OH_{(g)} \to H_{(g)} + O_{(g)}; \Delta H = 424 \ kJ$
The average bond energy (in $kJ$) for water is

Based on Hess's law calculations,what is the average $S-O$ bond energy in $SO_3$ if $\Delta H_f^o$ of $SO_3$ is $-270 \ kJ \ mol^{-1}$. Given: Bond energy of $O=O$ is $495 \ kJ \ mol^{-1}$,heat of sublimation for $S_{(s)}$ is $277 \ kJ \ mol^{-1}$,and bond energy of $S=O$ is not provided,but we assume the formation reaction: $S_{(s)} + \frac{3}{2} O_{2(g)} \rightarrow SO_{3(g)}$. Use the atomization energy of $S_{(s)} = 277 \ kJ \ mol^{-1}$ and $O=O = 495 \ kJ \ mol^{-1}$. Calculate the average $S-O$ bond energy in $SO_3$.

Which of the following has standard enthalpy of formation equal to zero?

When $50 \ cm^3$ of a strong acid is added to $50 \ cm^3$ of an alkali,the temperature rises by $5 \ ^oC$. If $250 \ cm^3$ of each liquid are mixed,the temperature rise would be $... \ ^oC$.

One mole of $C_2H_5OH_{(l)}$ was completely burnt in oxygen to form $CO_{2(g)}$ and $H_2O_{(l)}$. The standard enthalpy of formation $\Delta_fH^{\ominus}$ of $C_2H_5OH_{(l)}, CO_{2(g)}$ and $H_2O_{(l)}$ is $x, y, z \ kJ \ mol^{-1}$ respectively. What is $\Delta_rH^{\ominus}$ (in $kJ \ mol^{-1}$) for this reaction?

Given: $2Zn + O_2 \rightarrow 2ZnO, \Delta G^o = -616 \, J$; $2Zn + S_2 \rightarrow 2ZnS, \Delta G^o = -293 \, J$; $S_2 + 2O_2 \rightarrow 2SO_2, \Delta G^o = -408 \, J$. The value of $\Delta G^o$ for the reaction $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$ is ....... $J$.