For the reaction $MgCO_3(s) \rightarrow MgO(s) + CO_2(g)$,the value of $\Delta S$ is:

For a $Carnot$ engine,the source is at $500 \ K$ and the sink at $300 \ K$. What is the efficiency of this engine?

In which of the following processes is $\Delta S$ positive?

Two blocks of the same metal having same mass and at temperatures $T_1$ and $T_2$ respectively,are brought in contact with each other and allowed to attain thermal equilibrium at constant pressure. The change in entropy,$\Delta S,$ for this process is

State the limitation of the second law of thermodynamics.

Which one of the following has $\Delta S^o$ greater than zero?