What is the standard enthalpy of reaction (in $kJ$) when two moles of $Fe_2O_{3(s)}$ react with $H_2$ gas to give $Fe$ metal? $\Delta H_f^{\circ}$ of $Fe_2O_{3(s)}$ and $H_2O_{(l)}$ are $-824.2$ and $-285.83 \ kJ \ mol^{-1}$ respectively.

Under similar conditions,the enthalpy of freezing is exactly opposite to:

Given that:
$2C_{(s)} + 2O_{2(g)} \to 2CO_{2(g)}$; $\Delta H = -787 \ kJ$
$H_{2(g)} + \frac{1}{2} O_{2(g)} \to H_2O_{(l)}$; $\Delta H = -286 \ kJ$
$C_2H_{2(g)} + \frac{5}{2} O_{2(g)} \to 2CO_{2(g)} + H_2O_{(l)}$; $\Delta H = -1301 \ kJ$
Calculate the heat of formation of acetylene $(C_2H_{2(g)})$ in $kJ$.

$C + O_2 \to CO_2; \Delta H = X$
$CO + \frac{1}{2} O_2 \to CO_2; \Delta H = Y$
Then the heat of formation of $CO$ is

For the reaction $\frac{1}{2} X_2O_{(s)} \to X_{(s)} + \frac{1}{4} O_{2(g)}$ with $\Delta H = 90 \ kJ$,the enthalpy change for the reaction of $1 \ mol$ of $O_2$ with metal $X$ is ................ $kJ$.

If the standard enthalpy change $\left(\Delta_{r} H^\theta\right)$ for the reaction $H_{2(g)} + Br_{2(l)} \rightarrow 2 HBr_{(g)}$ is $-72.8 \ kJ$,the standard enthalpy of formation $\left(\Delta_{f} H^\theta\right)$ of $HBr_{(g)}$ (in $kJ \ mol^{-1}$) is