Question

Explain why

A) If heat flows from high to low temperatures, the entropy change in any process cannot be negative.

B) The specific heat of any substance is always lowest in the vapor (gas) phase.

Answer 1

A) Let high temperature reservoir be at temperature T_H and lower temperature reservoir be at temperature T_L. So change in entropy is

Now Second law of thermodynamics states that . So heat flows from high to low temperatures.

B)In vapor phase, there are almost no bonds between the constituent particles of the given substance. Hence less heat is required to increase the kinetic energies of the particles and hence raise the temperature of the gas.So the specific heat of any substance is always lowest in the vapor (gas) phase.