For the reaction $NH_4Cl_{(s)} \rightarrow NH_{3(g)} + HCl_{(g)}$,the entropy change is ...... .

At the boiling point of water,$900 \ J/g$ of heat is exchanged. What is the increase in entropy in $J \ K^{-1} \ mol^{-1}$?

Standard entropy of $X_2, Y_2$ and $XY_3$ are $60, 40$ and $50 \ J \ K^{-1} \ mol^{-1},$ respectively. For the reaction,$\frac{1}{2}X_2 + \frac{3}{2}Y_2 \to XY_3, \ \Delta H = -30 \ kJ,$ to be at equilibrium,the temperature will be ............... $K$.

Calculate $\Delta S_{total}$ for a certain reaction at $298 \ K$ if $\Delta H^{\circ} = -208.6 \ kJ$ and $\Delta S^{\circ} = -36 \ J \ K^{-1}$. (in $J \ K^{-1}$)

At $10\, ^oC$,$1\, mol$ of an ideal gas is allowed to expand reversibly and adiabatically from $10\, L$ to $200\, L$. Calculate the change in entropy in $cal/K$.

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 $-1648 \times 10^3 \ J \ mol^{-1}$)