Heat produced in calories by the combustion of one gram of carbon is called

Comment on the thermodynamic stability of $NO_{(g)}$,given:
$\frac{1}{2} N_{2(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{(g)}; \Delta_r H^{\ominus} = 90 \, kJ \, mol^{-1}$
$NO_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow NO_{2(g)}; \Delta_r H^{\ominus} = -74 \, kJ \, mol^{-1}$

When $2 \ mol$ of $C_2H_{6(g)}$ is completely combusted,it releases $3129 \ kJ$ of heat. What is the enthalpy of formation of $C_2H_{6(g)}$? The $\Delta H_f$ values for $CO_{2(g)}$ and $H_2O_{(l)}$ are $-395 \ kJ \ mol^{-1}$ and $-286 \ kJ \ mol^{-1}$ respectively.

Standard molar enthalpy of formation of $CO_2$ is equal to

If the ratio of the enthalpy of formation of $CO_2$ and $SO_2$ is $4:3$ and the enthalpy of formation of $CS_2$ is $26 \ kcal/mol$,then what will be the enthalpy of formation of $SO_2(g)$ based on the following reaction?
$CS_2(l) + 3O_2(g) \to CO_2(g) + 2SO_2(g)$

When it is not possible to calculate the enthalpy of a reaction experimentally,it can be calculated by .....