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

The values of heat of formation of $SO_2$ and $SO_3$ are $-298.2 \ kJ$ and $-395.2 \ kJ$ respectively. The heat of reaction for the following reaction will be $... \ kJ$
$SO_2 + \frac{1}{2}O_2 \to SO_3$

The enthalpy change for the reaction,$C_{2}H_{6(g)} \to 2C_{(g)} + 6H_{(g)}$ is $X \ kJ$. The bond energy of $C-H$ bond is :-

The $H-H$ bond energy is $430 \ kJ \ mol^{-1}$ and $Cl-Cl$ bond energy is $240 \ kJ \ mol^{-1}$. $\Delta H$ for the formation of $HCl$ is $-90 \ kJ \ mol^{-1}$. The $H-Cl$ bond energy is about:

Calculate the enthalpy change of vaporisation of benzene if $13 \ g$ of benzene vaporised by supplying $5.1 \ kJ$ of heat.

The enthalpy of $1 \ mol$ of a compound is equal to its ...... (when it is formed from its constituent elements).