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

Calculate the $\Delta_fH^{\circ}$ of $N_2H_{4(g)}$ given the following bond energies:
$B.E.(N-N) = 159 \ kJ \ mol^{-1}$
$B.E.(H-H) = 436 \ kJ \ mol^{-1}$
$B.E.(N \equiv N) = 941 \ kJ \ mol^{-1}$
$B.E.(N-H) = 398 \ kJ \ mol^{-1}$

The enthalpy change during a reaction does not depend on .......

The heat of combustion of carbon is $-94 \ kcal$ at $1 \ atm$ pressure. The internal energy of $CO_2$ is .... $kcal$.

The enthalpy change for the reaction $C(s) + O_2(g) \to CO_2(g)$ is:

Calculate the heat of formation of $HCl$ gas from the following reaction: $H_{2(g)} + Cl_{2(g)} \rightarrow 2 HCl_{(g)} ; \Delta H = -194 \ kJ$