Chemical Engineering Thermodynamics - Study Mode

[#231] In case of steady flow compression polytropic process (PV n = constant), the work done on air is the lowest, when
Correct Answer

(C) N = 1

Explanation

Solution: Area under $$p-v$$ xa0diagram is minimum when work is done on a system under isothermal conditions hence $$n=1.$$

[#232] Change of heat content when one mole of compound is burnt in oxygen at constant pressure is called the
Correct Answer

(C) Heat of combustion

Explanation

Solution: Heat of combustion is the change in heat content of the compound when one mole of that compound is burnt in the presence of oxygen. This type of reaction is where common in petroleum refinery where coke is combusted and removed.

[#233] Pick out the correct statement:
Correct Answer

(B) Under reversible conditions, the adiabatic work is less than isothermal work

Explanation

Solution: Under reversible conditions if we see the area under $$P-V$$ xa0plot the area is maximum in case of isothermal conditions hence the adiabatic work is less than isothermal work.

[#234] For a spontaneous process, free energy
Correct Answer

(C) Decreases whereas the entropy increases

Explanation

Solution: From second law of thermodynamics $$eqalign{
& TdS geqslant delta Q cr
& Rightarrow TdS geqslant dU + delta W cr} $$ For an irreversible process $$TdS - dU - delta W > 0$$ And for a reversible process $$TdS - dU - delta W = 0$$ For any spontaneous process there should be finite changes so, we can consider it as an irreversible process and we know for irreversible process from second law of thermodynamics by above discussion: $$TdS - dU - PdV > 0$$ Under constant temperature and volume process $$ - dF > 0 Rightarrow dF < 0$$ Similarly for an constant temperature and pressure process $$dleft( {TS - U - PV}
ight) > 0 Rightarrow dG < 0$$

[#235] A large iceberg melts at the base, but not at the top, because of the reason that
Correct Answer

(B) Due to the high pressure at the base, its melting point reduces

Explanation

Solution: We can say by Le Chatelier's principle on increasing the pressure the system will react in an way to minimize the effect( the volume decreases) so, generally substances tend to form solid but in case of water the as the liquid occupies less volume than solid the high pressure tends to form liquid (melting).