Chemical Engineering Thermodynamics - Study Mode

[#301] Fugacity and pressure are numerically equal, when the gas is
Correct Answer

(D) In ideal state

Explanation

Solution: We know the concept of fugacity is originated from the equation $$d{mu _i} = pdv - sdT$$ xa0 xa0for an pure gas. Under constant temperature and assuming an ideal gas we can write this as $$dmu = RTdlnP$$ xa0 xa0and for an real gas the same equation is assumed keeping all the non-ideality in the term fugacity and written as $$dmu = RTdlnf$$ So, we can say for an ideal gas $$f = p.$$

[#302] Lenz's law results from the law of conservation of
Correct Answer

(C) Energy

Explanation

Solution: Lenz’s law is derived from law of conservation of energy.

[#303] Entropy change for an irreversible isolated system is
Correct Answer

(D) > 0

Explanation

Solution: From second law of thermodynamics $$eqalign{
& TdS geqslant delta Q cr
& Rightarrow TdS geqslant dU + delta W cr} $$ For an irreversible process $$S - dU - delta W > 0.$$ xa0 xa0So, system undergoing irreversible change under constant internal energy and constant volume will have entropy change greater than zero $$dS>0.$$ And for an reversible process $$TdS - dU - delta W = 0.$$

[#304] What happens in a reversible adiabatic compression?
Correct Answer

(A) Heating occurs

Explanation

Solution: Here if we see the situation with respect to a throttling process where reversible adiabatic expansion takes place there the heating or cooling takes place depending upon the initial conditions because there we have two contravening effects. I. Increase in temperature due to viscous dissipation. II. Decrease in temperature as the pressure energy of the gas is decreased. But in case of reversible adiabatic compression we have same effect that means both the effects leads to increase in temperature only. Hence there will be heating.

[#305] The equation, PV = nRT, is best obeyed by gases at
Correct Answer

(A) Low pressure & high temperature

Explanation

Solution: The ideal behavior is usually shown at low pressures and high temperatures. One of the conclusion from this statement is that fugacity coefficient is one at low pressures.