Unit 4: Second Law of Thermodynamics

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Questions and Answers

What is the process during which the perfect conductor is removed and heat sink is brought in contact with cylinder head?

Reversible Adiabatic compression process

Isothermal compression process (correct)

Isothermal expansion process

Reversible Adiabatic expansion process

What is the efficiency of a Carnot engine dependent on?

The heat transfer rate during isothermal expansion

The work done during isothermal compression

The specific design of the engine

The temperature ratio of the hot and cold reservoirs (correct)

What is the maximum theoretical efficiency that any heat engine can achieve?

Q_h / Q_c

1 - (Q_c / Q_h)

W_out / Q_h

1 - (T_c / T_h) (correct)

What does the Carnot theorem state?

No heat engine operating between a given temperature source and a given temperature sink has a higher efficiency than a reversible engine Signup and view all the answers

What is the main reason for studying the second law of thermodynamics?

To understand the limitations of the first law of thermodynamics Signup and view all the answers

What is the temperature of the triple point of water on the absolute thermodynamic temperature scale?

273.16 K Signup and view all the answers

What is the absolute thermodynamic temperature scale based on?

Heat addition or heat rejection in a cycle Signup and view all the answers

What is the relationship between the thermodynamic temperature scale and the ideal gas law?

The thermodynamic temperature scale is based on the ideal gas law Signup and view all the answers

What is the primary function of a thermal reservoir?

To supply or absorb heat energy without changing its temperature Signup and view all the answers

What is the purpose of the reverse Carnot cycle?

To transfer heat from a colder body to a hotter body Signup and view all the answers

What does the first law of thermodynamics state about the direction of energy transfer?

Energy transfer can take place in either direction Signup and view all the answers

What is the expression for the efficiency of a heat engine?

η = (Q1-Q2)/Q1 Signup and view all the answers

What is the inequality of Clausius a statement of?

The second law of thermodynamics Signup and view all the answers

What is the limitation of the first law of thermodynamics?

It does not specify the direction of energy transfer Signup and view all the answers

What is the relationship between the coefficient of performance of a heat pump and the efficiency of a heat engine?

COP of a heat pump is the reciprocal of the efficiency of a heat engine Signup and view all the answers

What is the condition for a process to be perfectly reversible?

It must be internally, externally, mechanically and thermally reversible. Signup and view all the answers

What is an example of a process that satisfies the first law of thermodynamics but not the second law?

A liquid ice-cream solidifying without doing any work on it Signup and view all the answers

What is the purpose of a heat pump?

To transfer heat energy from a source to a sink Signup and view all the answers

What is entropy a measure of?

The amount of disorder or randomness in a system Signup and view all the answers

What is the main reason why a PMM-II is impossible according to the Kelvin-Planck statement?

It cannot convert internal energy into work. Signup and view all the answers

What is the purpose of the second law of thermodynamics?

To specify the direction of energy transfer Signup and view all the answers

What happens to the internal energy of the brakes when a running vehicle is stopped by applying brakes?

It increases by an amount equal to the decrease in kinetic energy Signup and view all the answers

Which of the following is a cause of irreversibility in a process?

All of the above. Signup and view all the answers

What is the main assumption made in the operation of a Carnot cycle?

The walls of the cylinder are perfectly insulated. Signup and view all the answers

What is the characteristic of the isothermal expansion process in a Carnot cycle?

The system expands isothermally at temperature T1. Signup and view all the answers

What is the primary effect of a cyclic process in a heat engine according to the Kelvin-Plank statement?

To convert only part of the heat supplied into work Signup and view all the answers

What is the purpose of a heat pump according to the Clausius statement?

To add energy in the form of work to transfer heat from a low temperature reservoir to a high temperature reservoir Signup and view all the answers

What is the violation of the Kelvin-Plank statement equivalent to?

Violation of the Clausius statement Signup and view all the answers

What is a Perpetual Motion Machine of the Second Kind (P.M.M.-II)?

A machine that converts internal energy into work with 100% efficiency Signup and view all the answers

What is the primary characteristic of a reversible process?

It can be performed in a reverse direction, restoring the system and surroundings to their initial condition Signup and view all the answers

What is the significance of entropy being a state function?

It means that only the change in entropy is important, not the absolute value. Signup and view all the answers

What is the relationship between entropy and the number of possible microstates in a system?

Higher entropy corresponds to a larger number of possible microstates. Signup and view all the answers

What is the principle of increase of entropy?

Entropy always increases over time in a closed system. Signup and view all the answers

What is the implication of energy degradation?

Energy becomes less available to do work as entropy increases. Signup and view all the answers

What is the relationship between entropy and disorder/randomness?

Entropy is a measure of disorder and randomness. Signup and view all the answers

What is the implication of irreversibility?

It is impossible to restore the initial state of a system. Signup and view all the answers

What is the significance of the second law of thermodynamics?

It is a fundamental concept in thermodynamics. Signup and view all the answers

What happens to entropy in a reversible process?

Entropy remains constant. Signup and view all the answers

What is the relationship between entropy and the amount of energy available to do work?

Entropy is a measure of the energy unavailable to do work. Signup and view all the answers

What is the implication of the principle of increase of entropy for the behavior of energy and matter?

It implies that energy and matter will always become more disorganized over time. Signup and view all the answers

Study Notes

Limitation of First Law of Thermodynamics

First law of thermodynamics states that energy is conserved, but it does not specify the direction of energy transfer.
The first law is necessary but not sufficient for a process to occur.
Examples of the limitation of the first law:
- Ice cream melting when left open to the atmosphere, but it does not solidify back without external work.
- Joule's experiment, where the fall of weight causes rotation of paddle and increases temperature of water, but increase in temperature of water does not lift the weight.
- A running vehicle stopping due to brakes, where the internal energy of brakes increases, but the hot brakes do not cause the wheels to rotate.

Basic Definitions

Thermal reservoir: a large system that can absorb or release energy as heat without changing its temperature.
Heat engine: a cyclically operating device that absorbs energy as heat from a high-temperature reservoir, converts part of it into work, and rejects the rest to a low-temperature reservoir.
Efficiency of a heat engine: ratio of work output to heat supply.
Heat pump: a device that transfers heat energy from a cold body to a hot body, using a small amount of external work.

Second Law of Thermodynamics

Kelvin-Planck statement: it is impossible to construct an engine that converts all the heat energy into work.
Clausius statement: it is impossible to construct a heat pump that transfers heat from a cold body to a hot body without external work.
Both statements are equivalent and imply that it is impossible to have a machine that violates the second law of thermodynamics.

Perpetual Motion Machines (PMM)

PMM-I: a machine that violates the first law of thermodynamics, producing work without energy input.
PMM-II: a machine that violates the second law of thermodynamics, converting internal energy into work with 100% efficiency.
Both types of PMM are impossible.

Concept of Reversibility and Irreversibility

Reversible process: a process that can be reversed without changing the system or surroundings.
Irreversible process: a process that cannot be reversed, resulting in a change in the system or surroundings.
Causes of irreversibility: friction, heat transfer, and other factors.

Carnot Cycle

A reversible cycle that consists of four processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
The Carnot cycle is the most efficient cycle possible, with an efficiency of 1 - (T_c / T_h), where T_c and T_h are the temperatures of the cold and hot reservoirs, respectively.

Carnot Theorem

All heat engines operating between a given temperature source and sink have an efficiency less than or equal to the Carnot engine.
The Carnot theorem is a fundamental limit on the efficiency of heat engines.

Absolute Thermodynamic Temperature Scale

A temperature scale based on the principles of thermodynamics, with the triple point of water defined as 273.16 K and absolute zero defined as 0 K.
The absolute temperature scale is a universal scale that is applicable to all systems, regardless of their composition or state.

Reverse Carnot Cycle (Carnot Refrigeration Cycle)

A cycle that operates in reverse, transferring heat from a cold body to a hot body using external work.### The Carnot Cycle
The Carnot cycle is a thermodynamic cycle that uses a refrigerant to transfer heat from a colder body to a hotter body.
The cycle consists of four stages: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
The reverse Carnot cycle is the basis for most refrigeration systems, including household refrigerators and freezers, industrial chillers, and cryogenic coolers.

The Inequality of Clausius

The inequality of Clausius states that (dQ/T) = 0, where dQ is the amount of heat transferred and T is the temperature at which the heat transfer occurs.
The inequality indicates that in a reversible process, the integral is equal to zero (S = Q/T), while in an irreversible process, the integral is less than zero (S > Q/T).
The inequality is a statement of the second law of thermodynamics, which dictates that the total entropy of an isolated system will always increase over time.

Entropy

Entropy is a measure of the amount of disorder, randomness, or uncertainty in a system.
Entropy can be thought of as a measure of the amount of energy in a system that is unavailable to do work.
Entropy is typically denoted by the symbol "S" and is measured in units of joules per kelvin (J/K).
Entropy is a state function, meaning that only the change in entropy (S) is important, not the absolute value.
Entropy can be related to the number of possible microstates in a system, with higher entropy corresponding to a larger number of possible microstates.

Principle of Increase of Entropy

The principle of increase of entropy states that the total entropy of an isolated system will always increase over time, except in reversible processes.
Entropy always increases over time in a closed system, remains constant in a reversible process, and never decreases spontaneously in an isolated system.
The principle has far-reaching implications, including energy degradation, disorder and randomness, and irreversibility.

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Explore the limitations of the first law of thermodynamics and learn about the principles of energy conservation. This quiz covers the basics of the second law of thermodynamics and its applications.