Entropy and Irreversibility MCQ Quiz in मल्याळम - Objective Question with Answer for Entropy and Irreversibility - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept-

• During the process of melting, the solid and liquid phases of a pure substance are in equilibrium with each other. The amount of heat required to convert one unit amount of substance from the solid phase to the liquid phase — leaving the temperature of the system unaltered — is known as the latent heat of fusion.
• If m kg of solid changes to liquid at a constant temperature which is its melting point, the heat absorbed by the substance or the latent heat of fusion formula is given by,  Q = mL

where L = specific latent heat of fusion of substance and m = mass of the solid.

Entropy (S) -

• It measures the degree of randomness or disorder in the system. The greater the disorder in an isolated system, the higher is the entropy.
• ∆S is related to q and T for a reversible reaction as - 

Where, Q_rev = is the heat and T = temperature.

Calculation:

Given 

Latent heat (L) = 318.5 kJ/kg and mass of ice = 90 kg

∴ Total heat (Q) = 90 × 318.5 = 28665 kJ

Entropy, 

Concept:

When the transfer of heat takes place through a finite temperature difference, there is a decrease in the availability of energy so transferred. Consider a reversible heat engine operating
between temperatures T₁ and T₀, Then

Q₁ = T₁ . ∆s

Q2 = T₀ ∆s

and W = A.E. = [T₁ – T₀] ∆s

Given:

The temperature of source, T₁= 1000K

The temperature of system, T2= 500K

The temperature of surroundings , To= 300K

Heat given by source ,Q = (-)7200 kJ/min {Heat given by the source is considered negative(-)}

Heat given to system ,Q =  7200 kJ/min  {Heat given to the source is considered positive(+)}

Entropy change of heat source, 

Entropy change of system, 

Net change of entropy,  

Concept:

Heat is transferred from hot gases to surrounding

using control volume entropy analysis on ABCD

̇Ṡ_in + Ṡ_gen - Ṡ_out = 

For steady state 

Ṡ_gen = Ṡ_out - Ṡ_in 

S_gen = 0.916

Explanation:

• Exergy (or) Available Energy: The maximum portion of energy that could be converted into useful work by ideal processes that reduce the system to a dead state(a state in equilibrium with the earth and its atmosphere).
  • W_max = I + W_act ,where I = Irreversibility (loss of available energy)
• Enthalpy: It is the total amount of energy contained within a system.
• Entropy: It is the degree of randomness of the system.

Explanation:

Entropy changes for a closed system:

Entropy change during the constant pressure process:

Entropy change during the constant volume process:

Entropy change during the constant temperature process:

Concept:

According to Clausius Equation:

Calculation:

Given:

Heat transferred to the surrounding (dQ) = -1 kJ = -1000 J

Temperature of the reservoir (T) = 527°C = 527 + 273 = 800 K

Entropy (dS) = dQ/T

Concept:

The entropy change of the universe or entropy generation is given as

ΔS_universe = ΔS_system + ΔS_surrounding

When heat is rejected to the surrounding then the temperature of the surrounding does not change, therefore,

The temperature of the system changes continuously, therefore, the entropy change of the system is given by

Where m is the mass of the system and T_i is the initial temperature of the system and T_f is the final temperature attained by the system and C is the specific heat of the system.

The heat interaction with the surrounding is given as

dQ = m × C × dT

where dT is the temperature difference between the system and the surrounding

Calculation:

Given, for potato m = 100 g, C = 3.5 kJ/kg.K and T_i = 120°C,

Since the potato attains thermal equilibrium with the surrounding then the final temperature of the potato is equal to the final temperature of the surrounding ∴ T_f = 30°C

dQ = m × C × dT

⇒ dQ = 0.1 × 3.5 × (120 – 30)

∴ Q = 31.5 kJ

ΔS_universe = ΔS_system + ΔS_surrounding

ΔS_universe = - 0.091 + 0.103 = 0.012 kJ/K = 12 J/K

Concept:

Entropy change of the universe is given by

Entropy change of the liquid is given by 

Where C_p is the specific heat of the liquid and the temperature is changed from T₁ to T₂

Entropy change of the surrounding is given by  here T is the ambient temperature which is constant.

Calculation:

Since it is given that the system is insulated therefore it will not exchange heat with the surrounding in that case the entropy change of the surrounding will be Zero, and the liquid temperature is increased from T₁ to T₂ and the specific heat of the liquid is C_p

Explanation:

If a closed system is undergoing an irreversible process, the change in entropy of the system is given by

dS > 0, or dS = 0, or dS

In an irreversible process in which heat is removed from the system then its entropy can decrease. 

The entropy of a closed system is given by

When the process is irreversible then entropy generation in the system (δs)gen is always positive, the heat transfer will decide whether the entropy will increase or decrease.

When heat is added to the system

∴  i.e. entropy increases

When Heat is removed from the system

∴  i.e. entropy increases decreases or remains constant

When the process is adiabatic, dQ = 0,

 i.e. entropy increases

∴ when a closed system is undergoing an irreversible process the entropy may increase, decrease or remain constant.

Concept:
Entropy change of a body is given by

Where dQ is the heat transfer taking place and T is the temperature of the body

Calculation:

Given:

T₁ = 1000 K, T₂ = 500 K, Q = 7200 kJ

Net entropy change = (ds)₂ – (ds)₁