Author: Fania Rashid
Thermodynamics is a fundamental branch of science that governs the behavior of energy transfer and transformation. From the engines that power our vehicles to the way our bodies regulate temperature, thermodynamics play an essential role in shaping the physical world. By understanding the core concepts of thermodynamics, we can gain insights into how energy is used, stored, and conserved in various systems.
Concept of System and Its Surroundings in Thermodynamic Universe
In thermodynamics, a system refers to a specific part of the universe that we choose to study. Everything outside this system is referred to as the surroundings, and together, they form the thermodynamic universe.
Types of Systems in Thermodynamics
Depending on how energy and matter interact, systems are classified into three main types:
1. Open System: A system that exchanges both energy and matter with its surroundings.
➢ Example: A boiling pot of water with no lid allows both steam (matter) and heat (energy) to escape.
2. Closed System: A system that allows energy exchange but no matter exchange.
➢ Example: A sealed pressure cooker transfers heat to and from its surroundings but does not allow steam to escape.
3. Isolated System: A system that does not exchange either energy or matter with its surroundings.
➢ Example: A thermos flask ideally prevents both heat loss and mass exchange with the environment, keeping a liquid hot or cold for a long time.
What are State Functions?
A state function is a property of a system that depends only on its current state, not on how it reached that state. It is similar to the concept of altitude, whether you climb a mountain or take a helicopter to the top, the height remains the same.
Common State Functions in Thermodynamics
• Temperature (T): Measures the intensity of heat within a system.
Example: A cup of coffee and a bowl of soup at 80°C have the same temperature, regardless of their size.
• Pressure (P): The force exerted per unit area.
Example: The pressure inside a sealed soda bottle increases when shaken because the gas molecules collide more frequently with the bottle’s walls.
• Volume (V): The amount of space occupied by the system.
Example: The volume of air inside a balloon expands when heated, demonstrating the relationship between temperature and gas volume.
• Internal Energy (U): The total energy contained within a system, including kinetic and potential energy.
• Enthalpy (H): The total heat content of a system, especially in chemical reactions.
Example: In combustion reactions, enthalpy changes determine the amount of heat released or absorbed.
Since state functions depend only on the current condition of a system, they are useful for thermodynamic calculations.
Intensive and Extensive Properties – Why Size Matters in Thermodynamics
The thermodynamic properties are classified into two categories based on whether they depend on the system’s size or not.
1. Intensive Properties
These properties do not depend on the amount of substance in the system.
Example: Temperature, pressure, and density remain the same whether measured in a small cup of water or an entire lake.
2. Extensive Properties
These properties depend on the total quantity of matter present in the system.
Example: Mass, volume, and total energy increase when the amount of substance increases.
Thermodynamic Equilibrium
A system is in thermodynamic equilibrium when all forms of equilibrium—thermal, mechanical, and chemical, are maintained simultaneously.
Types of Equilibrium in Thermodynamics
1. Thermal Equilibrium: No temperature difference exists within the system or with the surroundings.
Example: A glass of water left at room temperature will eventually reach the same temperature as its surroundings.
2. Mechanical Equilibrium: No unbalanced forces exist within the system.
Example: A balloon remains stationary when the internal pressure is equal to the external atmospheric pressure.
3. Chemical Equilibrium: No net chemical reactions occur, and the composition remains constant.
Example: In a sealed bottle of soda, the dissolved carbon dioxide remains in equilibrium with the gas phase until the bottle is opened.
Reversibility and Irreversibility in Thermodynamics
A reversible process is an idealized thermodynamic process that can be reversed without leaving any net change in the system or surroundings. However, most real-world processes are irreversible, meaning they involve losses due to factors such as friction, heat dissipation, or increase in entropy.
Examples of Reversible and Irreversible Processes
1. Reversible Process: The slow, controlled compression of a gas in a piston, where every step can be undone without loss.
2. Irreversible Process: The sudden bursting of a balloon, where energy is lost in the form of sound and kinetic energy.
Real-World Applications of Thermodynamics
Thermodynamics isn’t just confined to laboratories or textbooks; it governs everyday life. Here are a few practical applications:
1. Refrigerators and Air Conditioners: These appliances use thermodynamic cycles to transfer heat from a cooler region to a warmer one, keeping our food fresh and homes comfortable.
2. Car Engines: Internal combustion engines operate based on thermodynamic principles, converting fuel into mechanical work through heat and pressure changes.
3. Power Plants: Thermal power plants convert heat energy into electricity, optimizing energy transformation through controlled thermodynamic cycles.
4. Human Metabolism: Our bodies function like thermodynamic systems, converting food into energy and regulating heat to maintain homeostasis.
Conclusion
Thermodynamics is an integral part of our world, shaping everything from industrial technology to natural processes. By understanding the core concepts—systems and surroundings, state functions, intensive and extensive properties, equilibrium, and reversibility, we gain insights into how energy flows and transforms. Whether designing energy-efficient machinery, predicting chemical reactions, or simply understanding how heat affects daily life, thermodynamics offers a framework that explains the fundamental principles governing our universe. So, the next time you watch steam rise from a cup of coffee or feel the warmth of sunlight on your skin, remember—you’re witnessing thermodynamics in action!
Read More: Physical Chemistry
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