Identify the law for the statement "Overall the enthalpy change for a reaction is equal to the sum of enthalpy changes of individual steps in the reaction".

Calculate the enthalpy change for the reaction
$H_2 + F_2 \longrightarrow 2HF$
given that
Bond energy of $H-H$ bond $= 434 \ kJ/mol$
Bond energy of $F-F$ bond $= 158 \ kJ/mol$
Bond energy of $H-F$ bond $= 565 \ kJ/mol$
Result in $kJ$.

Calculate the amount of methane formed by the liberation of $149.6 \ kJ$ of heat using the following equation:
$C_{(s)} + 2H_{2(g)} \longrightarrow CH_{4(g)} \quad \Delta H = -74.8 \ kJ/mol$ (in $g$)

The enthalpy of combustion of carbon disulfide $(CS_2)$ is $-110.2 \, kJ \, mol^{-1}$. If the enthalpies of formation of $SO_2$ and $CO_2$ are $-297.4 \, kJ \, mol^{-1}$ and $-394.5 \, kJ \, mol^{-1}$ respectively,the enthalpy of formation of carbon disulfide is:

If the heat of combustion of $C$ is $-x \, kJ$,the heat of formation of $H_2O$ is $-y \, kJ$,and the heat of combustion of $CH_4$ is $-z \, kJ$,what is the heat of formation of $CH_4$?

In order to decompose $9 \ g$ of water,$142.5 \ kJ$ of heat is required. Hence,the enthalpy of formation of water is ...... $kJ/mol$.