The species which by definition has $ZERO$ standard molar enthalpy of formation at $298 \ K$ is

The heat of combustion of benzene determined in a bomb calorimeter is $-870 \ kcal \ mol^{-1}$ at $25 \ ^oC$. The value of $\Delta E$ for the reaction is......$kcal$.

$6$ moles of an ideal gas expand isothermally and reversibly from a volume of $1 \ L$ to a volume of $10 \ L$ at $27 \ ^oC$. What is the maximum work done? (in $kJ$)

What is the value of $\Delta H - \Delta U$ for the following reaction? $2 C_{(s)} + 3 H_{2(g)} \rightarrow C_2H_{6(g)}$

The volume of $100 \ L$ of gas increases to $120 \ L$ at a constant temperature and an external pressure of $10 \ bar$. Calculate the work done by the system. [Given: $1 \ L \ bar = 24.21 \ cal$] (in $cal$)

If the enthalpy of $B$ is greater than that of $A$,the reaction $A \to B$ is