Thermodynamics

Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy. It describes how thermal energy is transferred and transformed, and how it affects the macroscopic properties of matter. The four laws of thermodynamics provide a framework for understanding these processes.

The first law states that energy cannot be created or destroyed, only transferred or transformed. The second law states that the entropy of an isolated system always increases over time. The third law states that the entropy of a perfect crystal at absolute zero is zero. The fourth law states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

These laws have important implications for our understanding of the universe. For example, the second law of thermodynamics tells us that the universe is constantly becoming more disordered, and that eventually all the stars will burn out and the universe will reach a state of maximum entropy.

What is Thermodynamics?

What is Thermodynamics?

Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy. It is a fundamental science that has applications in many fields, such as engineering, chemistry, biology, and environmental science.

The basic principles of thermodynamics are based on the laws of thermodynamics, which describe how heat and energy behave in physical systems. The four laws of thermodynamics are:

• The Zeroth law of thermodynamics: If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
• The first law of thermodynamics: Energy cannot be created or destroyed, but it can be transferred from one form to another.
• The second law of thermodynamics: The entropy of an isolated system always increases over time.
• The third law of thermodynamics: The entropy of a perfect crystal at absolute zero is zero.

These laws provide a framework for understanding how heat and energy flow in physical systems. They can be used to predict the behavior of systems in a variety of situations, such as the operation of heat engines, the design of refrigeration systems, and the study of chemical reactions.

Examples of Thermodynamics

Here are some examples of how thermodynamics is applied in different fields:

• Engineering: Thermodynamics is used to design and optimize heat engines, refrigeration systems, and other devices that convert heat into work or work into heat.
• Chemistry: Thermodynamics is used to study chemical reactions and to predict the equilibrium composition of chemical systems.
• Biology: Thermodynamics is used to study the energy metabolism of cells and organisms, and to understand how living systems maintain homeostasis.
• Environmental science: Thermodynamics is used to study the transfer of heat and energy in the environment, and to understand the impact of human activities on the climate.

Thermodynamics is a powerful tool that can be used to understand a wide variety of phenomena in the natural world. It is a fundamental science that has applications in many fields, and it continues to be an active area of research.

The video is a rapid revision of thermodynamics for JEE Main, presented by Rakhi Ma’am through short notes and previous year questions (PYQs).

Rapid Revision of Thermodynamics for JEE Main

Short Notes

• Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy.
• The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
• The second law of thermodynamics states that the entropy of a closed system always increases over time.
• Entropy is a measure of the disorder of a system.
• Heat is the transfer of thermal energy from one object to another.
• Work is the transfer of energy from one object to another by means of a force.
• Internal energy is the sum of the kinetic and potential energies of the particles in a system.
• Enthalpy is the sum of the internal energy of a system and the product of its pressure and volume.
• Gibbs free energy is the maximum amount of work that can be done by a system at constant temperature and pressure.

Previous Year Questions (PYQs)

1. A gas is compressed from a volume of 10 L to a volume of 5 L. The pressure of the gas increases from 1 atm to 2 atm. What is the work done by the gas?

2. A 100 g block of ice at 0°C is placed in a calorimeter containing 100 g of water at 20°C. What is the final temperature of the mixture?

3. A heat engine operates between a hot reservoir at 100°C and a cold reservoir at 20°C. The engine does 100 J of work per cycle. What is the efficiency of the engine?

Solutions

1. The work done by the gas is given by the formula:

$$W = -P\Delta V$$

where:

• W is the work done (in joules)
• P is the pressure (in pascals)
• ΔV is the change in volume (in cubic meters)

In this case, P = 1 atm = 101,325 Pa, ΔV = -5 L = -0.005 m3, so:

$$W = -(101,325 Pa)(-0.005 m3) = 506.625 J$$

Therefore, the work done by the gas is 506.625 J.

2. The heat absorbed by the ice is given by the formula:

$$Q = mc\Delta T$$

where:

• Q is the heat absorbed (in joules)
• m is the mass of the ice (in kilograms)
• c is the specific heat capacity of ice (in joules per kilogram-kelvin)
• ΔT is the change in temperature (in kelvins)

In this case, m = 0.1 kg, c = 2090 J/kg-K, and ΔT = 20°C = 20 K, so:

$$Q = (0.1 kg)(2090 J/kg-K)(20 K) = 4180 J$$

Therefore, the heat absorbed by the ice is 4180 J.

The heat released by the water is given by the formula:

$$Q = mc\Delta T$$

where:

• Q is the heat released (in joules)
• m is the mass of the water (in kilograms)
• c is the specific heat capacity of water (in joules per kilogram-kelvin)
• ΔT is the change in temperature (in kelvins)

In this case, m = 0.1 kg, c = 4180 J/kg-K, and ΔT = -20°C = -20 K, so:

$$Q = (0.1 kg)(4180 J/kg-K)(-20 K) = -8360 J$$

Therefore, the heat released by the water is -8360 J.

The total heat absorbed by the mixture is:

$$Q = Q_{ice} + Q_{water} = 4180 J - 8360 J = -4180 J$$

Therefore, the final temperature of the mixture is:

$$T_f = T_i + \frac{Q}{mc}$$

where:

• Tf is the final temperature (in kelvins)
• Ti is the initial temperature (in kelvins)
• Q is the total heat absorbed (in joules)
• m is the total mass of the mixture (in kilograms)
• c is the specific heat capacity of the mixture (in joules per kilogram-kelvin)

In this case, Ti = 20°C = 293 K, Q = -4180 J, m = 0.2 kg, and c = 4180 J/kg-K, so:

$$T_f = 293 K + \frac{-4180 J}{(0.2 kg)(4180 J/kg-K)} = 273 K$$

Therefore, the final temperature of the mixture is 273 K, or 0°C.

3. The efficiency of a heat engine is given by the formula:

$$\eta = \frac{W}{Q_h}$$

where:

• η is the efficiency
• W is the work done (in joules)
• Qh is the heat absorbed from the hot reservoir (in joules)

In this case, W = 100 J and Qh = 100°C - 20°C = 80°C = 353 K, so:

$$\eta = \frac{100 J}{353 K} = 0.283$$

Therefore, the efficiency of the engine is 0.283, or 28.3%.

Basic Concepts of Thermodynamics – Thermodynamic Terms

Basic Concepts of Thermodynamics – Thermodynamic Terms

Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy. It is a fundamental science that has applications in many fields, such as engineering, chemistry, and biology.

Thermodynamic Terms

• System: A system is a region of space that is being studied. The system can be anything, from a single atom to the entire universe.
• Surroundings: The surroundings are everything outside of the system. The surroundings can interact with the system, but they are not part of the system.
• Boundary: The boundary is the surface that separates the system from the surroundings. The boundary can be real or imaginary.
• State: The state of a system is a complete description of the system’s properties. The state of a system can be specified by a number of variables, such as temperature, pressure, and volume.
• Process: A process is a change in the state of a system. A process can be caused by a change in the system’s surroundings, or it can be caused by a change in the system itself.
• Heat: Heat is the transfer of thermal energy from one system to another. Heat always flows from a hotter system to a colder system.
• Work: Work is the transfer of energy from one system to another by means of a force. Work can be done on a system, or it can be done by a system.
• Internal energy: The internal energy of a system is the sum of the kinetic and potential energies of the particles in the system. The internal energy of a system can be increased by adding heat to the system, or it can be decreased by doing work on the system.
• Entropy: Entropy is a measure of the disorder of a system. The entropy of a system can be increased by adding heat to the system, or it can be decreased by doing work on the system.

Examples of Thermodynamic Terms

• A cup of hot coffee: The cup of hot coffee is the system. The room temperature air is the surroundings. The boundary is the surface of the cup of coffee. The state of the system is specified by the temperature, pressure, and volume of the coffee. The process of drinking the coffee is a change in the state of the system. The heat that is transferred from the coffee to the person’s mouth is heat. The work that is done by the person to drink the coffee is work. The internal energy of the coffee is the sum of the kinetic and potential energies of the particles in the coffee. The entropy of the coffee is a measure of the disorder of the coffee.
• A car engine: The car engine is the system. The air and fuel mixture is the surroundings. The boundary is the surface of the engine. The state of the system is specified by the temperature, pressure, and volume of the air and fuel mixture. The process of combustion is a change in the state of the system. The heat that is released by the combustion is heat. The work that is done by the engine is work. The internal energy of the air and fuel mixture is the sum of the kinetic and potential energies of the particles in the air and fuel mixture. The entropy of the air and fuel mixture is a measure of the disorder of the air and fuel mixture.

Thermodynamics is a complex subject, but it is also a very important one. The basic concepts of thermodynamics can be used to understand a wide variety of phenomena, from the behavior of gases to the operation of heat engines.

Thermodynamic Properties

Thermodynamic Properties

Thermodynamic properties are physical properties that describe the state of a thermodynamic system. They are used to calculate the changes in energy, entropy, and other thermodynamic quantities that occur when a system undergoes a change in state.

The most common thermodynamic properties are:

• Temperature is a measure of the average kinetic energy of the particles in a system.
• Pressure is a measure of the force exerted by a system on its surroundings.
• Volume is a measure of the amount of space occupied by a system.
• Mass is a measure of the amount of matter in a system.
• Energy is a measure of the total amount of work that a system can do.
• Entropy is a measure of the disorder of a system.

These properties are related to each other by a number of thermodynamic equations, such as the ideal gas law:

$$PV = nRT$$

where:

• P is the pressure of the gas
• V is the volume of the gas
• n is the number of moles of gas
• R is the ideal gas constant
• T is the temperature of the gas

Thermodynamic properties can be used to calculate a number of other thermodynamic quantities, such as:

• Heat capacity is a measure of the amount of heat that a system must absorb to raise its temperature by one degree Celsius.
• Entropy change is a measure of the change in disorder of a system when it undergoes a change in state.
• Gibbs free energy is a measure of the maximum amount of work that a system can do at constant temperature and pressure.

Thermodynamic properties are essential for understanding the behavior of thermodynamic systems. They are used in a wide variety of applications, such as:

• Engineering
• Chemistry
• Biology
• Materials science
• Environmental science

Examples of Thermodynamic Properties

The following are some examples of thermodynamic properties:

• The temperature of a room is a measure of the average kinetic energy of the particles in the air in the room.
• The pressure of a tire is a measure of the force exerted by the air inside the tire on the tire’s walls.
• The volume of a balloon is a measure of the amount of space occupied by the balloon.
• The mass of a person is a measure of the amount of matter in the person’s body.
• The energy content of a food is a measure of the total amount of work that the food can do.
• The entropy of a deck of cards is a measure of the disorder of the deck of cards.

These are just a few examples of the many thermodynamic properties that exist. Thermodynamic properties are essential for understanding the behavior of thermodynamic systems and are used in a wide variety of applications.

Thermodynamics Solved Problems

Example 1: Calculating the Change in Internal Energy

A gas expands from a volume of 10 liters to 20 liters at a constant pressure of 1 atmosphere. The initial temperature of the gas is 25°C, and the final temperature is 50°C. Calculate the change in internal energy of the gas.

Solution:

The change in internal energy of a gas can be calculated using the formula:

ΔU = Q - W

where:

• ΔU is the change in internal energy
• Q is the heat added to the gas
• W is the work done by the gas

In this case, the heat added to the gas can be calculated using the formula:

Q = mcΔT

where:

• m is the mass of the gas
• c is the specific heat capacity of the gas
• ΔT is the change in temperature

The work done by the gas can be calculated using the formula:

W = -PΔV

where:

• P is the pressure of the gas
• ΔV is the change in volume

Substituting the given values into these formulas, we get:

Q = (1 mole)(20.79 J/mol-K)(50°C - 25°C) = 519.75 J
W = -(1 atm)(20 L - 10 L) = -101.325 J
ΔU = 519.75 J - (-101.325 J) = 621.075 J

Therefore, the change in internal energy of the gas is 621.075 J.

Example 2: Calculating the Heat Capacity of a Solid

A 100-gram sample of copper is heated from 25°C to 100°C. The heat added to the copper is 3.96 kJ. Calculate the heat capacity of copper.

Solution:

The heat capacity of a solid can be calculated using the formula:

c = Q/mΔT

where:

• c is the heat capacity
• Q is the heat added to the solid
• m is the mass of the solid
• ΔT is the change in temperature

Substituting the given values into this formula, we get:

c = (3.96 kJ)/(100 g)(100°C - 25°C) = 0.396 J/g-°C

Therefore, the heat capacity of copper is 0.396 J/g-°C.

Laws of Thermodynamics

The Laws of Thermodynamics

The laws of thermodynamics are a set of principles that describe how energy behaves in thermodynamic systems. They are used to predict the direction of spontaneous processes and to calculate the efficiency of heat engines.

The First Law of Thermodynamics

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. This means that the total amount of energy in a closed system remains constant.

For example, when you burn a piece of coal, the chemical energy stored in the coal is converted into heat energy. The total amount of energy in the system (the coal plus the air) remains the same.

The Second Law of Thermodynamics

The second law of thermodynamics states that the entropy of a closed system always increases over time. Entropy is a measure of the disorder of a system. The more disordered a system is, the higher its entropy.

For example, when you scramble an egg, the entropy of the egg increases. This is because the egg white and yolk are mixed together, and the molecules are no longer arranged in a regular pattern.

The Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is zero. This means that a perfect crystal is perfectly ordered, and there is no disorder.

The third law of thermodynamics is a consequence of the second law of thermodynamics. If the entropy of a system can never decrease, then it must approach zero as the temperature approaches absolute zero.

Applications of the Laws of Thermodynamics

The laws of thermodynamics have many applications in engineering, chemistry, and biology. Some examples include:

• The laws of thermodynamics are used to design heat engines, which convert heat energy into mechanical energy.
• The laws of thermodynamics are used to calculate the efficiency of refrigerators and air conditioners.
• The laws of thermodynamics are used to study chemical reactions and to predict the products of those reactions.
• The laws of thermodynamics are used to study biological processes, such as the metabolism of food.

The laws of thermodynamics are fundamental laws of nature that have a wide range of applications. They are essential for understanding how energy behaves in the universe.

Thermodynamics Examples in Daily Life

Thermodynamics Examples in Daily Life

Thermodynamics is the branch of physics that deals with heat and its relation to other forms of energy. It is a fundamental science that has applications in many areas of our daily lives, from the way our bodies function to the operation of our cars and homes.

Here are some examples of thermodynamics in daily life:

• The human body: Our bodies are constantly exchanging heat with our surroundings. When we are too hot, we sweat to cool down. When we are too cold, we shiver to generate heat. This process is regulated by our body’s thermostat, which is located in the hypothalamus.
• Cooking: When we cook food, we are using heat to change its chemical composition. For example, when we cook meat, the proteins in the meat break down and become more tender.
• Refrigeration: Refrigerators work by removing heat from food. This prevents the food from spoiling by slowing down the growth of bacteria.
• Air conditioning: Air conditioners work by removing heat from the air. This makes the air cooler and more comfortable to breathe.
• Heating: Heating systems work by adding heat to the air. This makes the air warmer and more comfortable to breathe.
• Transportation: Cars, trucks, and airplanes all use engines that convert heat into motion. This allows us to travel from one place to another.
• Power generation: Power plants use heat to generate electricity. This electricity is used to power our homes, businesses, and factories.

These are just a few examples of the many ways that thermodynamics affects our daily lives. It is a fundamental science that has a wide range of applications, from the way our bodies function to the operation of our cars and homes.

Thermodynamics – Summary and Overview

Frequently Asked Questions – FAQs

What is the importance of the laws of thermodynamics?

The laws of thermodynamics are fundamental principles that govern the behavior of energy and matter in the universe. They play a crucial role in various scientific fields, including physics, chemistry, biology, and engineering. Understanding the significance of these laws is essential for comprehending the workings of the universe and making advancements in technology.

First Law of Thermodynamics (Conservation of Energy):

• Statement: Energy cannot be created or destroyed, but it can be transferred or transformed from one form to another.
• Importance:
  • This law establishes the principle of energy conservation, ensuring that the total amount of energy in an isolated system remains constant.
  • It helps us understand and analyze energy transformations in various processes, such as heat transfer, work done, and chemical reactions.
  • The first law is crucial in designing efficient energy systems, such as engines, power plants, and refrigeration systems, by minimizing energy losses and optimizing energy conversion.

Second Law of Thermodynamics (Entropy and Disorder):

• Statement: In any isolated system, the entropy (a measure of disorder) always increases over time.
• Importance:
  • This law governs the direction of spontaneous processes and explains why certain changes occur naturally while others do not.
  • It helps us understand why heat flows from a hotter object to a colder one, why gases expand to fill a container, and why disorder tends to increase in closed systems.
  • The second law has profound implications for understanding the arrow of time, as it suggests that the universe tends towards increasing disorder over time.

Third Law of Thermodynamics (Absolute Zero):

• Statement: As the temperature of a system approaches absolute zero (-273.15°C), the entropy of the system approaches a minimum value.
• Importance:
  • This law provides a theoretical limit for the lowest temperature that can be achieved in a system.
  • It helps us understand the behavior of matter at extremely low temperatures, such as superconductivity and superfluidity.
  • The third law is crucial in studying the properties of materials and developing technologies for cryogenics and refrigeration.

Applications and Examples:

• Engineering: The laws of thermodynamics are essential in designing and optimizing engines, power plants, refrigeration systems, and other energy-conversion devices.
• Chemistry: Thermodynamics plays a vital role in understanding chemical reactions, equilibrium, and the spontaneity of processes.
• Biology: Thermodynamics helps explain energy transformations in biological systems, such as metabolism, photosynthesis, and cellular respiration.
• Cosmology: The laws of thermodynamics are fundamental in studying the evolution of the universe, including the Big Bang theory and the concept of entropy in the universe.

In summary, the laws of thermodynamics are of utmost importance in understanding the behavior of energy and matter in the universe. They provide a framework for analyzing energy transformations, predicting the direction of spontaneous processes, and studying the properties of matter at extreme conditions. These laws have far-reaching applications in various scientific fields and technological advancements, shaping our understanding of the world around us.

What is an example of negative work?

Negative work occurs when a force is applied to an object in the opposite direction of the object’s displacement. In other words, the force and displacement vectors are pointing in opposite directions. This results in a decrease in the object’s kinetic energy.

Here are some examples of negative work:

1. Pushing a book against a wall: When you push a book against a wall, the force you apply is in the opposite direction of the book’s displacement (which is zero since the book doesn’t move). This results in negative work.

2. Lifting a book up against gravity: When you lift a book up against gravity, the force you apply (upward) is in the opposite direction of the book’s displacement (downward). This results in negative work.

3. Pulling a sled against friction: When you pull a sled against friction, the force you apply is in the opposite direction of the sled’s displacement. This results in negative work.

In each of these examples, the force and displacement vectors are pointing in opposite directions, resulting in negative work. This means that the object’s kinetic energy decreases.

It’s important to note that negative work doesn’t necessarily mean that the object is moving in the opposite direction of the force. In the case of pushing a book against a wall, the book doesn’t move at all, but negative work is still done because the force and displacement vectors are pointing in opposite directions.

Can energy be destroyed or lost?

Can Energy be Destroyed or Lost?

Energy is a fundamental concept in physics, and it is often described as the ability to do work. It exists in many different forms, including heat, light, motion, and electricity. One of the key principles of thermodynamics is that energy cannot be created or destroyed, but it can be transferred or transformed from one form to another.

Examples of Energy Transformation

• Burning wood: When wood burns, the chemical energy stored in the wood is converted into heat energy and light energy.
• Hydroelectric power: When water flows through a turbine, the kinetic energy of the water is converted into electrical energy.
• Solar panels: When sunlight strikes a solar panel, the photons in the sunlight are converted into electrical energy.

Energy Conservation

The law of conservation of energy states that the total amount of energy in an isolated system remains constant. This means that energy cannot be created or destroyed, but it can be transferred or transformed from one form to another.

Examples of Energy Conservation

• A pendulum swinging: The total energy of a pendulum swinging back and forth remains constant. The kinetic energy of the pendulum is converted into potential energy as it rises, and then back into kinetic energy as it falls.
• A car driving: The total energy of a car driving down the road remains constant. The chemical energy stored in the gasoline is converted into kinetic energy as the car moves.

Energy Efficiency

Energy efficiency is a measure of how efficiently energy is used to perform a task. The more energy efficient a device is, the less energy it uses to perform the same task.

Examples of Energy Efficiency

• A light bulb: A light bulb that uses less energy to produce the same amount of light is more energy efficient.
• A car: A car that gets more miles per gallon is more energy efficient.

Conclusion

Energy cannot be created or destroyed, but it can be transferred or transformed from one form to another. The law of conservation of energy states that the total amount of energy in an isolated system remains constant. Energy efficiency is a measure of how efficiently energy is used to perform a task.

Fans convert electrical energy into mechanical energy – this is explained by which law?

Faraday’s Law of Electromagnetic Induction states that a changing magnetic field induces an electromotive force (EMF) in a conductor. This EMF can then cause an electric current to flow in the conductor, which can be used to power a motor or other device.

In a fan, the electric current flows through a coil of wire that is wrapped around a metal core. The core is made of a ferromagnetic material, which means that it can be easily magnetized. When the electric current flows through the coil, it creates a magnetic field around the core. This magnetic field then interacts with the magnetic field of the permanent magnets that are located on the stator of the fan.

The interaction between the two magnetic fields causes the rotor of the fan to rotate. The rotor is attached to the blades of the fan, so as the rotor rotates, the blades also rotate. This rotation of the blades creates a flow of air, which is what we feel as a breeze when we stand in front of a fan.

Here is a simplified example of how Faraday’s Law of Electromagnetic Induction works:

• Imagine a metal rod that is moving through a magnetic field.
• As the rod moves through the magnetic field, it experiences an EMF.
• This EMF causes an electric current to flow in the rod.
• The direction of the electric current is determined by the direction of the magnetic field and the direction of the rod’s motion.
• The strength of the electric current is determined by the strength of the magnetic field and the speed of the rod’s motion.

This is a very basic example, but it illustrates the fundamental principles of Faraday’s Law of Electromagnetic Induction. This law is used in a wide variety of devices, including fans, motors, generators, and transformers.

Does the human body obey the laws of thermodynamics?

Does the human body obey the laws of thermodynamics?

Yes, the human body obeys the laws of thermodynamics. The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. This means that the total amount of energy in the universe is constant. The second law of thermodynamics states that entropy, or disorder, always increases in a closed system. This means that over time, things tend to become more disorganized.

The human body is a closed system, meaning that it does not exchange energy or matter with its surroundings. Therefore, the total amount of energy in the human body is constant. However, the body does transform energy from one form to another. For example, when we eat food, we convert the chemical energy in the food into mechanical energy that we use to move.

The second law of thermodynamics also applies to the human body. Over time, the body becomes more disorganized. This is evident in the aging process, as our bodies become less efficient at converting energy and more susceptible to disease.

However, the human body is also able to maintain a state of homeostasis, or equilibrium. This is due to a number of feedback mechanisms that help to regulate the body’s temperature, pH, and other vital functions. These feedback mechanisms help to keep the body in a state of balance, even though entropy is always increasing.

Examples of how the human body obeys the laws of thermodynamics:

• When we eat food, we convert the chemical energy in the food into mechanical energy that we use to move. This is an example of the first law of thermodynamics, which states that energy cannot be created or destroyed, only transferred or transformed.
• When we sweat, we lose water and electrolytes, which can lead to dehydration. This is an example of the second law of thermodynamics, which states that entropy, or disorder, always increases in a closed system.
• As we age, our bodies become less efficient at converting energy and more susceptible to disease. This is also an example of the second law of thermodynamics, as the body becomes more disorganized over time.

The human body is a complex system that obeys the laws of thermodynamics. By understanding these laws, we can better understand how the body works and how to keep it healthy.