Thermodynamics Chapter: Second Law of Thermodynamics

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Questions and Answers

What is the primary focus of the second law of thermodynamics?

The directionality of irreversible processes (correct)

The capacity to do work

The transfer of energy by force

The conservation of energy

What is an example of an irreversible process?

A plant growing in the direction of sunlight

A glass bottle shattering on the ground (correct)

A rubber ball bouncing back up

A car moving forward on a flat road

What is the definition of work in the context of thermodynamics?

The capacity to do work

The measure of disorder in a system

The transfer of energy by a force acting on an object as it is displaced (correct)

The transfer of energy by heat

What is the ultimate consequence of the second law of thermodynamics stated in terms of entropy?

Entropy cannot decrease (A) Signup and view all the answers

What is a characteristic of entropy in a system?

A measure of the disorder or disorganization of a system (B) Signup and view all the answers

What happens to entropy during an irreversible process, such as heat transfer from a hot to a cold object?

Entropy increases (D) Signup and view all the answers

What is the relationship between the temperature of objects and the direction of heat transfer?

Heat transfers from objects with higher temperature to objects with lower temperature (B) Signup and view all the answers

What is the consequence of increasing entropy in a system?

The amount of usable energy in the system must decrease. (C) Signup and view all the answers

What is the principle of a Carnot engine?

It only uses reversible processes to achieve maximum efficiency. (D) Signup and view all the answers

What is the statement of Clausius' theorem?

Heat transfer must occur from a higher-temperature body to a lower-temperature body. (A) Signup and view all the answers

What is the Kelvin-Planck statement?

It is impossible to construct a device that operates on a cycle and produces the net equivalent of work to the heat transferred to the device. (D) Signup and view all the answers

What is the change in entropy in a reversible process?

<ol start="0"> <li>(C)</li> </ol> Signup and view all the answers

What is the direction of heat flow in a refrigerator?

From cold to hot. (B) Signup and view all the answers

What is the result of burning fuel to drive an engine?

The entropy of the system increases. (C) Signup and view all the answers

Why is it impossible to construct a device that operates on a cycle and produces the net equivalent of work to the heat transferred to the device?

Because heat cannot be converted completely into useful work. (C) Signup and view all the answers

Study Notes

Second Law of Thermodynamics

Describes the directionality of processes that can be described by the first law of thermodynamics.
Stems from the fact that some processes are irreversible, meaning they only occur in one direction.

Irreversible Processes

Examples: aging, a glass bottle shattering on the ground, and heat transfer from a hot to a cold object.
Work is the transfer of energy by a force acting on an object as it is displaced.
Energy is the capacity to do work.

Entropy

A measure of the disorder or disorganization of a system.
The second law of thermodynamics states that the total entropy of a system either remains constant or increases.
The entropy cannot decrease during a process of some system.
Entropy increases during heat transfer from a hot to a cold object.

Consequences of Entropy

As entropy increases, a certain amount of energy becomes permanently unavailable to do work.
The amount of usable energy in a system over time must decrease.

Carnot Cycle

Named after 19th-century French engineer Nicolas Sadi Carnot.
The greatest possible efficiency of a heat engine occurs in one that only uses reversible processes (entropy = 0).
A Carnot engine operates at the highest possible efficiency at any heat engine operating between two given temperatures.

Clausius' Theorem

Heat transfer must occur from a higher-temperature body to a lower-temperature body.
An obvious consequence of entropy and the second law of thermodynamics.

Kelvin-Planck Statement

It is impossible to construct a device that operates on a cycle and produces the net equivalent of work to the heat transferred to the device.
Heat cannot be converted completely into useful work.

Derivation of the Second Law of Thermodynamics

Carnot determined the efficiency of the Carnot engine to be: η = 1 - (Tc / Th).
The change in entropy (S) can be defined as the ratio of heat over temperature, for reversible processes.
For real, irreversible processes, the total change in entropy can be calculated as ΔS = Qc / Tc - Qh / Th.

Applications of the Second Law of Thermodynamics

Heat flow can be leveraged in applications such as refrigerators and heat engines to either cool or heat a space.
Examples: refrigerators, heat engines, and burning of fuel to drive an engine.

Examples of the Second Law of Thermodynamics

Burning of fuel to drive an engine, such as the gasoline that fuels an automobile.
Aging is another spontaneous, irreversible process that cannot be undone and moves in one direction.

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Description

Learn about the Second Law of Thermodynamics, which describes the directionality of irreversible processes, such as aging and heat transfer. Understand how it builds upon the First Law of Thermodynamics.