Chemical Engineering Thermodynamics MCQ Questions & Answers

41

dW and d_q are not the exact differential, because q and W are

A) State functions B) Path functions C) Intensive properties D) Extensive properties

Discuss

Answer & Solution

Answer: Option B

Solution:

As heat and work are path functions we can’t determine the amounts involved simply by connecting the end points.

42

For a constant volume process

A) dE = C_pdT B) dE = C_vdT C) dQ = dE + pdV D) dW = pdV

Discuss

Answer & Solution

Answer: Option B

Solution:

Since, under constant volume process the expansion work is zero, and by the definition of $${C_V}$$ we can write $${C_V} = \mathop {\lim }\limits_{\delta T \to 0} {\left( {\frac{{\delta Q}}{{\delta T}}} \right)_V}$$
By first law of thermodynamics
$$\eqalign{ & \delta Q = dU \cr & \Rightarrow dU = CvdT. \cr} $$

43

Pick out the correct statement.

A) Like internal energy and enthalphy, the absolute value of standard entropy for elementary substances is zero B) Melting of ice involves increase in enthalpy and a decrease in randomness C) The internal energy of an ideal gas depends only on its pressure D) Maximum work is done under reversible conditions

Discuss

Answer & Solution

Answer: Option D

Solution:

Since in case of reversible processes no losses are involved we can obtain maximum work from the system or maximum work Is done by the system.

44

Which of the following equations is obtained on combining 1^st and 2^nd law of thermodynamics, for a system of constant mass?

A) dE = Tds - PdV B) dQ = C_vdT + PdV C) dQ = C_pdT + Vdp D) Tds = dE - PdV

Discuss

Answer & Solution

Answer: Option A

Solution:

By second law of thermodynamics we can write $$TdS = \delta Q$$
Which is valid only for reversiable process but once it is connected to state variable by using first law of thermodynamics we can say it is valid for both reversible and irreversible process and the relation is: $$dU=TdS-PdV.$$

45

For an exothremic reaction

A) Only enthalpy change (ΔH) is negative B) Only internal energy change (ΔE) is negative C) Both ΔH and ΔE are negative D) Enthalpy change is zero

Discuss

Answer & Solution

Answer: Option C

Solution:

During exothermic reaction since the heat is given out by the system the thermal energy decreases and therefore the internal energy decreases leading to a decrease in enthalpy.

46

For an ideal gas, the enthalpy

A) Increases with rise in pressure B) Decreases with rise in pressure C) Is independent of pressure D) Is a path function

Discuss

Answer & Solution

Answer: Option C

Solution:

The enthalpy of a substance is given by $$dH = {C_P}dT + \left[ {V - T{{\left( {\frac{{\partial V}}{{\partial T}}} \right)}_P}} \right]dP$$
For ideal gas $$T{\left( {\frac{{\partial V}}{{\partial T}}} \right)_P} = V$$
So, $$dH = {C_P}dT$$
So, it is dependent on temperature only.

47

Refrigerants commonly used for domestic refrigerators are

A) Ethyl chloride or methyle chloride B) Freon-12 C) Propane D) NH₃ or CO₂

Discuss

Answer & Solution

Answer: Option A

Solution:

Domestic refrigerants are ethyl chloride or methyl chloride.

48

Which of the following is true for Virial equation of state?

A) Virial co-efficients are universal constants B) Virial co-efficients C) Virial co-efficients are function of temperature only D) For some gases, Virial equations and ideal gas equations are the same

Discuss

Answer & Solution

Answer: Option C

Solution:

Virial co-efficients are functions of temperature only.

49

A reasonably general expression for vapour-liquid phase equilibrium at low to moderate pressure is Φ_i y_i P = Y_i x_i f_i° where, Φ is a vapor fugacity component, Y_i is the liquid activity co-efficient and f_i° is the fugacity of the pure component i. the K_i value (Y_i = K_i x_i) is therefore, in general a function of

A) Temperature only B) Temperature and pressure only C) Temperature, pressure and liquid composition x_i only D) Temperature, pressure, liquid composition x_i and vapour composition y_i

Discuss

Answer & Solution

Answer: Option C

No explanation is given for this question. Let's Discuss on Board

50

Pick out the wrong statement.

A) The net change in entropy in any reversible cycle is always zero B) The entropy of the system as a whole in an irreversible process increases C) The entropy of the universe tends to a maximum D) The entropy of a substance does not remain constant during a reversible adiabatie change

Discuss

Answer & Solution

Answer: Option D

Solution:

We know for reversible process $$TdS = \delta Q$$ and since in adiabatic process $$\delta Q = 0 \Rightarrow TdS = 0$$
So reversible adiabatic process is an isentropic process.

Chemical Engineering Thermodynamics MCQ Questions & Answers | Chemical Engineering