For the complete combustion of ethanol,$C_2H_5OH_{(l)} + 3O_{2(g)} \rightarrow 2CO_{2(g)} + 3H_2O_{(l)}$,the amount of heat produced as measured in a bomb calorimeter is $1364.47 \ kJ \ mol^{-1}$ at $25 \ ^oC$. Assuming ideality,the enthalpy of combustion,$\Delta_cH$,for the reaction will be: $(R = 8.314 \ J \ K^{-1} \ mol^{-1})$ .....$kJ \ mol^{-1}$

For the reaction:
$CH_{4(g)} + 2O_{2(g)} \to CO_{2(g)} + 2H_2O_{(l)}$;
$\Delta_r H_{300} = -212.7 \ Kcal/mol$.
The absolute value of $\Delta_r U_{300}^o$ for this reaction is ....... $Kcal/mol$ $(R = 2 \ cal/mol-K)$.

For a reaction $2 CO_{(g)} + O_{2(g)} \rightleftharpoons 2 CO_{2(g)}$,$\Delta_{r} G^0 = -128 \ kJ$ at $300 \ K$. If $\Delta_{r} S^0$ of the reaction is $-40 \ J \ K^{-1}$,calculate $\Delta_{r} U$ of the reaction. (in $kJ$)

$C_{(graphite)} + O_{2(g)} \to CO_{2(g)}; \Delta H = - 94.05 \ k \ cal \ mol^{-1}$
$C_{(diamond)} + O_{2(g)} \to CO_{2(g)}; \Delta H = - 94.50 \ k \ cal \ mol^{-1}$
Therefore:

An ideal gas is expanded from $(p_1, V_1, T_1)$ to $(p_2, V_2, T_2)$ under different conditions. The correct statement$(s)$ among the following is(are):
[$A$] The work done on the gas is maximum when it is compressed irreversibly from $(p_2, V_2)$ to $(p_1, V_1)$ against constant pressure $p_1$.
[$B$] The work done by the gas is less when it is expanded reversibly from $V_1$ to $V_2$ under adiabatic conditions as compared to that when expanded reversibly from $V_1$ to $V_2$ under isothermal conditions.
[$C$] The change in internal energy of the gas is $(i)$ zero,if it is expanded reversibly with $T_1=T_2$,and $(ii)$ positive,if it is expanded reversibly under adiabatic conditions with $T_1 \neq T_2$.
[$D$] If the expansion is carried out freely,it is simultaneously both isothermal as well as adiabatic.

The heats of combustion of $CH_4, C_2H_6, C_2H_4$,and $C_2H_2$ at the same temperature are $-212.8, -373.0, -337.0$,and $-310.5 \, Kcal$ respectively. Which of these gases is the best fuel?