What is entropy?

The entropy change for the conversion of $1 \, \text{mol}$ of liquid water to steam at $373 \, K$ is ...... $J/K$ (Given: $\Delta H_{\text{vap}} = 2.257 \, kJ/g$). (in $0.9$)

One mole of an ideal gas expands adiabatically and reversibly from its initial pressure to half of its initial pressure. What will be the value of $\Delta S$ in $J \ K^{-1} \ mol^{-1}$? $[ln 2 = 0.693$ and $R = 8.314 \ J \ mol^{-1} \ K^{-1}]$

State the limitation of the $2^{nd}$ law of thermodynamics.

For the reactions,
$2 Cl_{(g)} \longrightarrow Cl_{2(g)}$
$CO_{2(g)} \longrightarrow CO_{(g)} + \frac{1}{2} O_{2(g)}$
What are the signs of $\Delta S$,respectively?

For a spontaneous endothermic process at constant pressure,which of the following is true?