The enthalpy change at $298 \ K$ for the decomposition of water is given in the following two steps:
Step $I$: $H_2O_{(g)} \to H_{(g)} + OH_{(g)}$; $\Delta H = 498 \ kJ \ mol^{-1}$
Step $II$: $OH_{(g)} \to H_{(g)} + O_{(g)}$; $\Delta H = 428 \ kJ \ mol^{-1}$
The average bond enthalpy of the $O-H$ bond is $.... \ kJ \ mol^{-1}$

The heats of combustion of rhombic and monoclinic sulphur are respectively $70960 \ cal$ and $71030 \ cal$. What will be the heat of conversion of rhombic sulphur to monoclinic? $(cal)$

Which of the following compounds has a standard molar enthalpy of formation equal to zero at $298 \ K$?

Which of the following reactions is endothermic?

Given the following thermochemical equations:
$(i) \ H_{2(g)} + \frac{1}{2}O_{2(g)} \rightarrow H_2O_{(l)} ; \Delta H = -68.39 \, kcal$
$(ii) \ K_{(s)} + H_2O_{(l)} + aq \rightarrow KOH_{(aq)} + \frac{1}{2}H_{2(g)} ; \Delta H = -48.0 \, kcal$
$(iii) \ KOH_{(s)} + aq \rightarrow KOH_{(aq)} ; \Delta H = -14.0 \, kcal$
Calculate the heat of formation of $KOH_{(s)}$.

Which of the following is an exothermic reaction?