Entropy Calculations- Entropy Calculations for a System, Surrounding and Universe, in Isothermal and Adiabatic Processes, Practice Problems and FAQs

I am staying in a house of say 1000sq.foot and You stay in a house of 2000 square feet. Let us add one room extra of 100 square feet Who will feel of having more space, You or me?
I have added 100 square feet to the existing 1000 square feet an increase of 10%
You have added 100 square feet to the existing 2000sq.ft- an increase of only 5%.
So, I will feel more freedom of movement than you.

increase in living space

Similarly, the increase in freedom (entropy) of the system depends on the relative increase in enthalpy with temperature
The overall change in entropy is given as
You shall understand the change in entropy under different conditions:

Table of Contents

Entropy Change for a System for an Ideal Gas
Entropy Change for a Surrounding
Change in entropy of universe for Reversible isothermal Process
Change in entropy of universe for Irreversible isothermal Process
Change in entropy of universe for Reversible Adiabatic Process
Change in entropy of universe for Irreversible Adiabatic Process
Entropy Change for Phase Transformation
Practice Problems
Frequently Asked Questions

Entropy Change for a System for an Ideal Gas

The entropy change of a system is given as follows: dsvsdvsd

We assumed that the process is reversible while deriving the equation; however, because entropy is a state function, the equation is valid for both reversible and irreversible processes given the same change in circumstances.
Using the ideal gas equation

ascca

Entropy Change for a Surrounding

csdcds

xzv

Change in entropy of universe for Reversible isothermal Process

cacsaa dsvvs

Change in entropy of universe for Irreversible isothermal Process

dfvdf

Total entropy change:

vsdvds vdfvd

Change in entropy of universe for Reversible Adiabatic Process

fvsdvs

vsdvds

Change in entropy of universe for Irreversible Adiabatic Process

vsvsf

csdcsd

Entropy Change for Phase Transformation

All phase transitions are reversible and occur at constant pressure and temperature.
Since heat is exchanged at constant pressure, qP= ΔH dvssdv

disorderliness and entropy change during melting of ice

fdss

disorderliness and entropy change during vaporization of water

Practice Problems

Q1. When 1.00 mole of H₂O(l) is generated under standard conditions, calculate the entropy change (JK^-1) in the surroundings (at 300 K). (Assume that △_rH^o = –300 kJmol^-1).

1 JK^-1
1000 JK^-1
969 JK^-1
887 JK^-1

regrg

Q2. Because the direct translation from A to B is difficult, the following path is followed:

guigi

ΔS(A ⟶ C) = 50 JK^-1
ΔS(C ⟶ D) = 30 JK^-1
ΔS(B ⟶ D) = 20 JK^-1
Find the entropy change for the process A ⟶ B.

Solution: Since entropy is a state function,

ΔS(A ⟶B) = ΔS(A⟶C) + ΔS(C⟶D) + ΔS(D⟶B)

= ΔS(A⟶C) + ΔS(C⟶D) − ΔS(B⟶D) (since ΔS(D⟶B) = − ΔS(B⟶D))

= (50 + 30 − 20) JK^-1 = 60 JK^-1

Hence the entropy change for the process A ⟶ B is 60 JK^-1.

Q3. Calculate the entropy change (JK^-1) that occurs when 3 mol of an ideal gas expands from a volume of 100 dm3 to a volume of 1000 dm3 at 300K in an isothermal reversible expansion.

38.3 JK^-1
574.4 JK^-1
57.44 JK^-1
383 JK^-1

Solution: The entropy change of a system is given as cdsdv

Q4. At 250 K, one mole of an ideal gas in thermal contact with the environment expands isothermally from 1 L to 3 L under the constant pressure of 5 atm. Find the change in the entropy of the surroundings (△S_surr) in JK^-1 during this phase.
(1 L atm = 101.3 J)

5.763 JK^-1
0.405 JK^-1
−1.013 JK^-1
−5.763 JK^-1

Solution: Change in entropy of the surrounding is given by, dsvsv

Frequently Asked Questions

Question 1. What does entropy mean in everyday life?
Answer. The amount of thermal energy or heat per temperature is measured by entropy. Some entropy examples in your kitchen include a campfire, ice melting, salt or sugar dissolving, popcorn cooking, and boiling water.

Question 2. Is it possible to have a negative value of entropy?
Answer. The measure of disorder in a system is entropy. Entropy is always rising as everything in the universe strives toward a more chaotic state. The entropy of the cosmos for spontaneous events is always rising, according to the second rule of thermodynamics. As a result, the total entropy can never be negative.

Question 3. Is it possible to eliminate entropy?
Answer. Entropy is created everywhere and constantly, at every scale, and it can't be removed by any means at any scale. The Second Law of Thermodynamics states that "entropy of an isolated, closed system (or cosmos) is always rising." This is a required but not sufficient condition.

Question 4. Is entropy increased by freezing?
Answer. Entropy favours melting because water has higher entropy than ice. Freezing is an exothermic process, which means that energy is lost from the water and dissipated in the environment. As a result, as the environment becomes hotter, it gains more energy, increasing the entropy of the environment.

Related Topics

Enthalpy of Neutralization

Enthalpy of Combustion

Enthalpy of solvation

Thermodynamic Processes

Enthalpy of formation