$C + O_2 \to CO_2; \Delta H = X$
$CO + \frac{1}{2} O_2 \to CO_2; \Delta H = Y$
Then the heat of formation of $CO$ is

Based on Hess's law calculations,what is the average bond energy of $S-O$ in $SO_3$ if $\Delta H_f^o$ of $SO_3$ is $-270 \ kJ \ mol^{-1}$. The bond energy of $O=O$ is $495 \ kJ \ mol^{-1}$ and the heat of sublimation for $S_{(s)}$ is $277 \ kJ \ mol^{-1}$? (Given: Bond energy of $S=O$ is not provided,assume the reaction $S_{(s)} + \frac{3}{2} O_2(g) \rightarrow SO_3(g)$). Note: The provided values in the prompt were inconsistent with standard chemical data; using standard values: $\Delta H_{sub}(S) = 277 \ kJ \ mol^{-1}$,$BE(O=O) = 495 \ kJ \ mol^{-1}$,$BE(S-O) = 330 \ kJ \ mol^{-1}$ is not the goal,we calculate based on the provided logic.

Calculate the enthalpy change for the reaction $H_{2(g)} + Br_{2(g)} \rightarrow 2HBr_{(g)}$ in $kJ$. The bond energies of $H-H$,$Br-Br$,and $H-Br$ are $435$,$192$,and $364 \, kJ \, mol^{-1}$ respectively.

$H_{2(g)} + \frac{1}{2}O_{2(g)} \rightarrow H_2O_{(l)}$; $\Delta H_{298K} = -68.32 \, kcal$. The enthalpy of vaporization of water at $25 \, ^\circ C$ and $1 \, atm$ pressure is $10.52 \, kcal$. Calculate the standard enthalpy of formation of $1 \, mole$ of water vapor at $25 \, ^\circ C$ (in $kcal$).

Equal volumes of methanoic acid and sodium hydroxide are mixed. If $x$ is the heat of formation of water,then the heat evolved on neutralization is

When $4 \ g$ of iron is burnt to ferric oxide at constant pressure,$29.28 \ kJ$ of heat is evolved. What is the enthalpy of formation of ferric oxide in $kJ \ mol^{-1}$? (At. Wt. of $Fe = 56$)