What is enthalpy of reaction?

The heat of formation of $SiO_2$ and $MgO$ is respectively $-48.4 \ kJ$ and $-34.7 \ kJ$. The heat of the reaction $2Mg + SiO_2 \to 2MgO + Si$ is $...... \ kJ$.

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.

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 of formation of sucrose $(C_{12}H_{22}O_{11})$ in $kJ \, mol^{-1}$ using the following data:
$(i) \, C_{12}H_{22}O_{11} + 12O_2 \to 12CO_2 + 11H_2O, \, \Delta H = -5200.7 \, kJ \, mol^{-1}$
$(ii) \, C + O_2 \to CO_2, \, \Delta H = -394.5 \, kJ \, mol^{-1}$
$(iii) \, H_2 + \frac{1}{2}O_2 \to H_2O, \, \Delta H = -285.8 \, kJ \, mol^{-1}$

The enthalpy of solution of anhydrous $CuSO_4$ is $-15.9 \, kcal$ and that of $CuSO_4 \cdot 5H_2O$ is $2.8 \, kcal$. The enthalpy of hydration of $CuSO_4$ is ..... $kcal$. (in $.7$)