Calculate the enthalpy change for the following reaction:
$H_2C=CH_{2(g)} + H_{2(g)} \longrightarrow H_3C-CH_{3(g)}$
[The bond energies of $C-H, C-C, C=C$ and $H-H$ are $414, 347, 615$ and $435 \ kJ/mol$ respectively.] (in $kJ$)

$H^{+}_{(aq)} + OH^{-}_{(aq)} \rightarrow H_2O_{(l)} + 56 \text{ kJ/mol}$. The heat of neutralization for the complete neutralization of $1 \text{ mole}$ of $H_2SO_4$ will be ...... $\text{kJ}$.

The reaction $CH_{4(g)} + Cl_{2(g)} \to CH_3Cl_{(g)} + HCl_{(g)}$ has $\Delta H = -25 \, kcal$. Given bond energies $BE(C-H) = 84 \, kcal$,$BE(H-Cl) = 103 \, kcal$,$BE(C-Cl) = x$,and $BE(Cl-Cl) = y$. If $\frac{x}{y} = \frac{9}{5}$,then find the value of $y$. (in $, kcal$)

Fill in the blanks:
$(i)$ The enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states is called the ....... of that compound.
$(ii)$ The total heat change in a chemical reaction is equal to the algebraic sum of the heat changes of the individual steps of the reaction. This law was given by .......... .
$(iii)$ $A$ process during which there is no exchange of heat between the system and the surroundings is called an ........... process.

The absolute enthalpy of neutralisation of the reaction $MgO_{(s)} + 2HCl_{(aq)} \to MgCl_{2(aq)} + H_2O_{(l)}$ will be

For the reaction $H_{2(g)} + C_{2}H_{4(g)} \rightarrow C_{2}H_{6(g)}$,the enthalpy change is ....... $Kcal \, mol^{-1}$. Given bond energies: $H-H = 103$,$C-H = 99$,$C-C = 80$,and $C=C = 145 \, Kcal \, mol^{-1}$.