Chemical Engineering Thermodynamics - Study Mode
[#316] Specific/molar Gibbs free energy for a pure substance does not change during
Correct Answer
(D) Either A, B or C
Explanation
Solution: During the phase change the gibbs free energy doesn’t change since the pressure and temperature are remained constant during phase change. For single component and closed system : $$dG = VdP - SdT$$
[#317] 1 st law of thermodynamics is nothing but the law of conservation of
Correct Answer
(C) Energy
Explanation
Solution: The first law of thermodynamics is an conservation of energy which states that energy cant be destroyed energy can be converted from one from to other but energy is not destroyed during the process and the energy of an isolated system always remans constant. $$delta Q = dU + delta W$$
[#318] Melting of wax is accompanied with __________ in entropy.
Correct Answer
(A) Increase
Explanation
Solution: Since here the solid or semi solid state is converting to liquid state the freedom of molecules is increasing hence randomness increases thereby, entropy which is an measure of randomness also increases.
[#319] Joule-Thomson co-efficient for a perfect gas is
Correct Answer
(A) Zero
Explanation
Solution: For a perfect gas since, the enthalpy depends only on temperature and the joule Thomson coefficient which is ratio of temperature change to pressure change at constant enthalpy. Since for an perfect gas the enthalpy remaining constant leads to temperature constancy the joule Thomson coefficient becomes zero.
[#320] Activity co-efficient is a measure of the
Correct Answer
(A) Departure from ideal solution behaviour
Explanation
Solution: Activity coefficient [{{gamma }_{i}}=frac{{{oversetfrown{{{f}_{l}}}}^{real}}}{oversetfrown{{{f}_{l}}^{ld}}}] For an ideal solution activity coefficient $$= 1$$ And for real solution it tells about the departure from ideal solution by real solution like compressibility factor in case of gases.