The standard heats of formation in $kcal \ mol^{-1}$ of $NO_{2(g)}$ and $N_2O_{4(g)}$ are $8.0$ and $2.0$ respectively. The heat of dimerization of $NO_2$ in $kcal$ for the reaction $2NO_{2(g)} \rightarrow N_2O_{4(g)}$ is:

The value of the enthalpy of neutralization of an acid and a base is significant only when $......$

At $1 \ bar$ and $298 \ K$,the standard molar enthalpy of formation of which substance is zero?

Calculate the heat required to convert $9 \ g$ of liquid water to water vapor using the following equations:
$H_{2(g)} + 1/2 O_{2(g)} \longrightarrow H_2O_{(g)} \quad \Delta H = -57 \ kCal$
$H_{2(g)} + 1/2 O_{2(g)} \longrightarrow H_2O_{(l)} \quad \Delta H = -68.3 \ kCal$ (in $kCal$)

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

In an exothermic reaction,$\Delta H$ is