For an isolated system,$\Delta U = 0,$ what will be $\Delta S?$

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

Identify the correct statement regarding a spontaneous process.

According to the second law of thermodynamics,which of the following is true for a spontaneous process?

Explain entropy and spontaneity of reactions.

For a sample of a perfect gas,when its pressure is changed isothermally from $p_i$ to $p_f$,the entropy change is given by: