Third Law Of Thermodynamics MCQ - Practice Questions with Answers

The entropy of any pure crystalline substance approaches zero as the temperature approaches absolute zero. This is called the third law of thermodynamics.

• At any pressure, the entropy of every crystalline solid in thermodynamic equilibrium at absolute zero is zero.

• It is impossible to reduce the temperature of any system to absolute zero by any process. 

• As the absolute temperature approaches zero, increment in entropy for isothermal process in crystalline solids approaches zero, 

i.e. S=0 at T=0

Or

If molar heat capacities of a substance (Cp) are measured at different temperature temperature  and a graph between Cp/T vs T is drawn and it shows this type of behaviour.

Now let be the entropy of the substance  at zero Kelvin and SM is its molar entropy at Kelvin then 

The area under the curve or graph of Cp/T vs T determined from zero Kelvin to any desired temperature would be molar entropy change going from zero to desired T.