What is the change in entropy when an ideal gas expands into a vacuum?

The entropy change for the expansion of $2 \, \text{mol}$ of an ideal gas from $2 \, \text{L}$ to $20 \, \text{L}$ at a temperature of $27 \, ^oC$ is ...... $(R = 2 \, \text{cal/mol K})$

For the oxidation of iron:
$4 Fe_{(s)} + 3 O_{2(g)} \rightarrow 2 Fe_2O_{3(s)}$
The entropy change is $-549.4 \ J \ K^{-1} \ mol^{-1}$ at $298 \ K$. Despite the negative entropy change of this reaction,why is the reaction spontaneous?
($\Delta_r H^\Theta$ for this reaction is $-1648 \times 10^3 \ J \ mol^{-1}$)

When a liquid boils,there is

$18 \ g$ of ice is converted into water at $0 \ ^\circ C$ and $1 \ atm$. The entropies of $H_2O_{(s)}$ and $H_2O_{(l)}$ are $38.2$ and $60 \ J/mol \ K$ respectively. The enthalpy change for this conversion is ..... $J/mol$.

If the standard molar entropies $(S^o)$ for $H_2$,$Cl_2$,and $HCl$ are $0.13$,$0.22$,and $0.19 \, kJ \, K^{-1} \, mol^{-1}$ respectively,what is the total change in standard entropy $(\Delta S^o)$ for the reaction $H_2 + Cl_2 \rightarrow 2HCl$ in $J \, K^{-1} \, mol^{-1}$?