$CH_4 + \frac{1}{2}O_2 \to CH_3OH$ is an exothermic reaction $(\Delta H < 0)$. If the enthalpies of combustion of $CH_4$ and $CH_3OH$ are $x$ and $y$ respectively,which of the following relations is correct?

If $38.55 \ kJ$ of heat is absorbed when $6.0 \ g$ of $O_2$ reacts with $ClF$ according to the reaction $2ClF_{(g)} + O_{2(g)} \longrightarrow Cl_2O_{(g)} + OF_{2(g)}$. What is the standard enthalpy of reaction (in $kJ$)?

Using the given reaction enthalpies,find the enthalpy of formation of $H_2O_2(l)$ in $kJ/mol$.
$(i) N_2H_4(l) + 2H_2O_2(l) \rightarrow N_2(g) + 4H_2O(l); \Delta_r H_1^\circ = -818 \, kJ/mol$
$(ii) N_2H_4(l) + O_2(g) \rightarrow N_2(g) + 2H_2O(l); \Delta_r H_2^\circ = -622 \, kJ/mol$
$(iii) H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l); \Delta_r H_3^\circ = -285 \, kJ/mol$

What will be the amount of heat evolved by burning $0.4 \ mol$ of methane? (Given heats of formation of $CH_4$,$CO_2$,and $H_2O$ are $-75$,$-400$,and $-240 \ kJ \ mol^{-1}$ respectively) ..... $kJ$

$2.1 \ g$ of $Fe$ combines with $S$ evolving $3.77 \ kJ$. The heat of formation of $FeS$ in $kJ/mol$ is

The enthalpy change for the reaction $C(s) + O_2(g) \to CO_2(g)$ is: