Скачать или смотреть 07a t Thermodynamics | First law of thermodynamics | Enthalpy change | Heat Capacity

🔥 First Law of Thermodynamics (Law of Energy Conservation)
• Definition: The first law of thermodynamics is essentially the law of conservation of energy applied to thermodynamic systems. It tells us that the change in a system’s internal energy () is equal to the heat supplied to the system () minus the work done by the system ():

• Key Idea:
• Heat (Q): Energy transferred due to temperature difference.
• Work (W): Energy transferred when the system does mechanical work (like expansion against pressure).
• Internal Energy (U): The total microscopic energy of molecules (kinetic + potential).
• Implication:
• Energy is not lost; it only shifts between heat, work, and internal energy.
• For example, in an engine, fuel’s chemical energy becomes heat, which partly converts into mechanical work, while some remains as internal energy.
• Processes that obey the law:
• Isothermal process: Heat absorbed equals work done.
• Isochoric process: No work is done, so heat directly changes internal energy.
• Adiabatic process: No heat exchange, so work done changes internal energy.
🔁 Reversible vs Irreversible Work Done in Thermodynamics
In thermodynamics, the work done by a system during expansion or compression depends on the path taken. Let’s break it down:
🔄 Reversible Work:
• Occurs when the system changes state infinitesimally slowly, maintaining equilibrium at every step.
• The external pressure is almost equal to the internal pressure.
• Maximum work is obtained in this idealised process.
• Example: Slow expansion of gas in a piston where pressure adjusts continuously.
❌ Irreversible Work:
• Happens when the system changes state rapidly or spontaneously, disrupting equilibrium.
• External pressure is not equal to internal pressure.
• Work done is less than reversible work due to energy losses (like friction, turbulence).
• Example: Sudden expansion of gas into a vacuum (free expansion). Thermodynamics is the science of energy transformations—essential for understanding chemical reactions, spontaneity, and equilibrium. At @PSINGHCHEMISTRY, we break it down for NEET, JEE, and Board aspirants with clarity and precision.

🔥 What is Thermodynamics?
Thermodynamics is the branch of chemistry that deals with energy changes in physical and chemical processes. It helps us answer three fundamental questions:
• Will a reaction occur?
• In which direction will it proceed?
• How far will it go?
🧪 Key Concepts You’ll Master at @PSINGHCHEMISTRY:
• System and Surroundings: Learn to define the boundaries of a chemical system and understand how energy flows between the system and its surroundings.
• Types of Systems: Open, closed, and isolated systems—each with unique energy exchange rules.
• State Functions: Properties like enthalpy (H), entropy (S), and internal energy (U) that define the state of a system.
• Laws of Thermodynamics:
• First Law: Energy can neither be created nor destroyed—only transformed.
• Second Law: Entropy of the universe always increases in spontaneous processes.
• Third Law: As temperature approaches absolute zero, entropy approaches a minimum.
⚙️ Why It Matters for NEET & JEE:
Understanding thermodynamics is crucial for solving problems on:
• Heat exchange and calorimetry
• Gibbs free energy and spontaneity