What is standard $N \equiv N$ bond enthalpy from following reaction,

$$\begin{aligned} & \mathrm{N}_2(g)+3 \mathrm{H}_2(g) \longrightarrow 2 \mathrm{NH}_3(g) ; \Delta H^{\circ}=-83 \mathrm{~kJ} \\ & \left(\Delta H^{\circ}(\mathrm{H}-\mathrm{H})=435 \mathrm{~kJ} ; \Delta H^{\circ}(\mathrm{N}-\mathrm{H})=389 \mathrm{~kJ}\right) \\ \end{aligned}$$

For the reaction,

$$\mathrm{N}_2(g)+3 \mathrm{H}_2(g) \longrightarrow 2 \mathrm{NH}_3(g) ; \Delta H$$

is equal to

When 6.0 g of graphite reacts with dihydrogen to give methane gas, 37.4 kJ of heat is liberated. What is standard enthalpy of formation of $\mathrm{CH}_4(\mathrm{~g})$ ?

Work done when 2 mole of an ideal gas is compressed from a volume of $$5 \mathrm{~m}^3$$ to $$2.5 \mathrm{~m}^3$$ at 300 K, under a pressure of 100 kpa is