2B2 Thermodynamics

Question 1

Define:

Thermodynamics

Answer 1

The study of the relationship of heat, work, and temperature in physical systems.

This discipline also defines principles that govern the behavior of an observed system and its interaction with the surroundings.

Question 2

How does thermodynamics explain energy transformations in physical processes?

Answer 2

It describes how energy is conserved, transferred, and transformed.

These principles are governed by the laws of thermodynamics.

Question 3

Name the four laws of thermodynamics.

Answer 3

• Zeroth Law: Defines thermal equilibrium.
• First Law: Conservation of Energy.
• Second Law: Entropy increases over time in closed systems.
• Third Law: Absolute zero is unattainable.

The laws assess the system’s ability to perform useful work by studying energy changes.

Question 4

Explain why thermodynamics is important in engineering and technology.

Answer 4

For designing efficient systems like engines, power plants, and refrigeration by optimizing energy use.

It underpins the development of sustainable energy technologies.

Question 5

Fill in the blank:

A closed system can exchange ______ but not ______ with its surroundings, while an isolated system exchanges neither.

Answer 5

energy, matter

Isolated systems are idealized and rare in practice, as perfect isolation is nearly impossible.

Question 6

What does the First Law of Thermodynamics state?

Answer 6

The total energy in an isolated system is conserved: energy cannot be created or destroyed, only transferred or converted from one form to another.

This is also known as the law of conservation of energy in thermal processes.

Question 7

Fill in the blank:

The first law of thermodynamics is expressed mathematically as ______.

Answer 7

ΔU = Q - W

ΔU is the change in internal energy, Q is heat added to the system, and W is work done by the system.

Question 8

What happens to the internal energy of a system if no heat is added but work is done on it?

Answer 8

The internal energy increases.

This follows ΔU = Q - W, where Q = 0, so ΔU = -(-W) = +W.

Question 9

True or false:

Heat transfer occurs in an adiabatic process.

Answer 9

False

In an adiabatic process, Q = 0, so energy change is due to work done only.

Question 10

What happens to internal energy when an air-filled balloon is compressed with no heat loss?

Answer 10

The internal energy of the gas increases, causing a rise in temperature.

This is an adiabatic process where work increases internal energy (ΔU = W).

Question 11

How does the first law of thermodynamics apply to a closed system?

Answer 11

Energy within the system is conserved; any energy added as heat will either increase internal energy, or do work.

Closed systems do not exchange matter with surroundings, only energy.

Question 12

Explain how a heat engine operates under the first law of thermodynamics.

Answer 12

A heat engine converts heat into work, with some energy always lost as heat to a low-temperature sink, with no net energy gain or loss.

With a heat engine, only energy transformation occurs. This efficiency limitation is tied to the first law.

Question 13

Fill in the blank:

In an isothermal process, the internal energy change (ΔU) is ______.

Answer 13

Zero

In an isothermal process, the temperature remains constant. The internal energy depends on the temperature. Therefore, the change in internal energy is zero. In this type of process, all heat added to the system is used to perform work.

Question 14

True or false:

A system performing work on its surroundings always loses internal energy.

Answer 14

False

If heat is added to the system, the internal energy may increase despite work being done.

Question 15

Define:

Isochoric process

Answer 15

A constant-volume process where no work is done, so ΔU = Q.

Since W = 0, energy change is only due to heat transfer (Q).

Question 16

How does the First Law of Thermodynamics apply to a refrigerator?

Answer 16

It ensures energy is conserved as the system removes heat from a cool space and expels it to a warmer area.

Work is required to move heat against its natural flow.

Question 17

Fill in the blank:

A heating system applies the first law by converting ______ or ______ energy into heat energy.

Answer 17

electrical; chemical

Examples include electric heaters and gas furnaces.

Question 18

True or False:

Hydroelectric power generation follows the first law of thermodynamics.

Answer 18

True

Dams transform the stored potential energy of elevated water into kinetic energy as it moves through a turbine, which is then used to generate electricity.

Question 19

Explain how the first law applies to batteries.

Answer 19

Batteries convert chemical energy into electrical energy, following energy conservation.

The energy output matches the chemical energy used minus any losses.

Question 20

How does the first law of thermodynamics explain engine efficiency?

Answer 20

It ensures that the work done by the engine equals the heat added minus the heat lost.

This principle applies to both internal combustion and steam engines.

Question 21

What is the Second Law of Thermodynamics?

Answer 21

The disorder in a system (entropy) increases with time; not all energy is converted to usable energy.

A portion of energy transforms into a form that cannot perform useful work.

Question 22

Fill in the blank:

Entropy measures the degree of ______ in a system.

Answer 22

randomness or disorder

Higher entropy means greater disorder and less available energy for work.

Question 23

True or false:

A perfectly efficient machine that creates no waste heat violates the second law of thermodynamics.

Answer 23

True

Such a machine (perpetual motion of the second kind) is impossible due to entropy.

Question 24

Explain the relationship between entropy and energy dispersal.

Answer 24

Entropy measures the spread or dispersal of energy in a system.

Greater dispersal means higher entropy.

Question 25

# Define: Spontaneous process

Answer 25

A **natural process that occurs without external input** and increases total entropy of the system and surroundings. ## Footnote Examples of spontaneous processes include heat flow from hot to cold or diffusion of gases in an open space.

Question 26

# True or false: Spontaneous processes **always increase entropy** in an isolated system.

Answer 26

True ## Footnote The Second Law ensures entropy in isolated systems never decreases.

Question 27

# Fill in the blank: A process is **reversible** if it can return to its initial state without leaving changes in the surroundings, whereas **irreversible** processes permanently increase the system's \_\_\_\_\_\_.

Answer 27

entropy ## Footnote Reversible processes are idealized and do not occur naturally, unlike irreversible processes which dominate in real-world systems.

Question 28

What is the formula to calculate the **change in entropy (ΔS)** of a system?

Answer 28

ΔS = Q/T ## Footnote ΔS = Entropy change, Q = Heat (J), T = Temp (K).

Question 29

Explain why the **entropy** of a system increases when it **absorbs heat (Q > 0)**.

Answer 29

When a system absorbs heat (Q > 0), its entropy increases because added thermal energy **increases the disorder** of the particles. ## Footnote Entropy measures the level of randomness or disorder in a system.

Question 30

Why is a substance in the **liquid phase** considered **more disordered** than in the solid phase?

Answer 30

Because in the liquid phase, particles have **greater freedom of movement** and occupy less structured positions compared to the fixed arrangement in the solid phase. ## Footnote This is related to entropy (second law of thermodynamics), which increases with disorder.

Question 31

# Fill in the blank: **Water freezing** in a refrigerator does not violate the second law of thermodynamics because the overall \_\_\_\_\_\_ of the system and surroundings increases as **heat is released into the environment**.

Answer 31

entropy ## Footnote While the entropy of the water decreases as it freezes, the heat released into the surroundings increases the entropy of the environment, ensuring the total entropy rises.

Question 32

A **refrigerator** moves heat from cold to hot. Why doesn’t this violate the **second law** of thermodynamics?

Answer 32

Because the refrigerator **uses external work** to transfer heat against the gradient. ## Footnote The Second Law allows heat transfer if work is done on the system.

Question 33

# True or false: The **second law** explains why no process can be 100% efficient.

Answer 33

True ## Footnote Energy is dissipated as heat increases system entropy, reducing efficiency.

Question 34

# Fill in the blank: The **Second Law** requires combustion engines to release \_\_\_\_\_ \_\_\_\_\_.

Answer 34

waste heat ## Footnote This prevents energy conversion violations and maintains system entropy balance.

Question 35

How does the **second law** affect **power plants**?

Answer 35

It **limits efficiency** due to unavoidable heat loss to surroundings. ## Footnote This principle applies to thermal and nuclear power plants.

Question 36

How does **thermal imaging** relate to the **second law** of thermodynamics?

Answer 36

It **detects heat transfer** from objects, showcasing the natural flow of heat from hot to cold regions. ## Footnote The second law explains the spontaneous heat flow observed in thermal imaging processes.

Question 37

Explain how **steam turbines** utilize the **second law** of thermodynamics in their operation.

Answer 37

They convert heat from steam into mechanical energy, with unavoidable **energy loss due to entropy**. ## Footnote The second law explains why not all heat energy can be transformed into useful work.

Question 38

# True or false: A substance at **absolute zero** has no particle motion.

Answer 38

True ## Footnote At absolute zero (0 K), particle motion theoretically stops.

Question 39

What is the **Third Law** of Thermodynamics?

Answer 39

As temperature approaches **absolute zero**, the **entropy** of the system reaches a **constant** value. ## Footnote Absolute zero is 0K (Kelvin), equivalent to -273°C.

Question 40

# True or false: It is possible to **reach absolute zero**.

Answer 40

False ## Footnote The third law states that reaching absolute zero is unattainable.

Question 41

# True or false: **Thermal equilibrium** occurs when two systems in contact **exchange energy** at equal rates.

Answer 41

True ## Footnote At thermal equilibrium, the systems have the same temperature.

Question 42

# Fill in the blank: The third law suggests **entropy** approaches a \_\_\_\_\_ value at **absolute zero**.

Answer 42

constant ## Footnote This applies in theoretical and practical cooling processes.

Question 43

How does the **third law** of thermodynamics apply to **cryogenics**?

Answer 43

It predicts that absolute zero is unattainable, **setting a temperature limit** for cryogenics. ## Footnote Systems approach absolute zero asymptotically.

Question 44

# True or false: The **third law** helps explain changes in **material properties** at low temperatures.

Answer 44

True ## Footnote Properties like thermal conductivity and specific heat become nearly constant.

Question 45

What is the **Zeroth Law** of Thermodynamics?

Answer 45

If two bodies are each in thermal equilibrium with a third body (A = C and B = C ), then the **two original bodies are in thermal equilibrium with each other (A = B)**. ## Footnote This law formalizes the concept of temperature in thermodynamics.

Question 46

# True or false: **Thermal equilibrium** means no net heat transfer occurs between systems.

Answer 46

True ## Footnote This condition occurs when systems have the same temperature.

Question 47

Provide an **example** of the **Zeroth Law** of Thermodynamics.

Answer 47

Food left outside the fridge reaching thermal equilibrium with the room and with each other. ## Footnote This demonstrates **heat transfer** until thermal equilibrium is achieved.

Question 48

How does the **zeroth law** of thermodynamics enable the **calibration of thermometers**?

Answer 48

The zeroth law ensures that if a thermometer is in **thermal equilibrium** with a reference system, it can reliably measure the temperature of other systems. ## Footnote This principle is the foundation of temperature measurement standards.

Question 49

How does a mercury **thermometer** operate in relation to the **Zeroth Law**?

Answer 49

It receives **heat** from the human body, causing the **mercury to expand** until thermal equilibrium is reached. ## Footnote The level of mercury indicates the corresponding temperature.

Question 50

What are the **three processes** that occur in any **heat engine**?

Answer 50

* Heat absorption from a hot reservoir. * Work performed by the system. * Heat rejection to a cold reservoir. ## Footnote These processes follow the **first and second laws** of thermodynamics.