Thermodynamics

1. Introduction to Thermodynamics

Definition: Study of energy, heat, work, and how they interact.

Importance: Explains how energy transfer affects physical systems.

2. Basic Concepts and Laws

(a) System and Surroundings

• System: The part of the universe under study.
• Surroundings: Everything outside the system.

(b) Types of Systems

• Open System: Exchanges both energy and matter.
• Closed System: Exchanges only energy.
• Isolated System: Exchanges neither energy nor matter.

3. First Law of Thermodynamics (Law of Conservation of Energy)

Statement:

Where:

• ΔU: Change in internal energy of the system.
• Q: Heat added to the system.
• W: Work done by the system.

Explanation: Energy cannot be created or destroyed, only transferred or converted.

Real-life Example:

Heating a soup on the stove: Heat energy (Q) increases the internal energy (ΔU). Stirring does work (W) on the soup, adding to the energy.

4. Second Law of Thermodynamics

Statement: Heat naturally flows from hot to cold, and entropy (disorder) tends to increase.

Change in entropy:

Where:

• ΔS: Change in entropy.
• Q_rev: Reversible heat transfer.
• T: Absolute temperature.

Real-life Example:

Ice melting into water at room temperature increases entropy because molecules become more disordered.

5. Zeroth Law of Thermodynamics

Statement: If two systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Implication: Temperature is a fundamental property.

6. Work and Heat in Thermodynamic Processes

Work done by/on the system: Mechanical movement, expansion, compression.

Heat transfer: Conduction, convection, radiation.

Equation for work in expansion:

Where:

• P: Pressure.
• ΔV: Change in volume.

Daily Life Example:

Pumping a bicycle tire: Compressing air increases pressure and temperature inside; opening the valve allows air to flow out, transferring energy as work and heat.

7. Ideal Gas Law

Where:

• P: Pressure.
• V: Volume.
• n: Moles of gas.
• R: Universal gas constant.
• T: Temperature in Kelvin.

Unique Real-life Example:

Inflating a balloon: Increasing the amount of air (n) or temperature (T) affects pressure and volume, following the ideal gas law.

8. Entropy and Irreversibility

Irreversible processes: Friction, mixing, spontaneous heat flow, increase entropy.

Reversible processes: Idealized, no entropy production.

Summary of Key Equations

Unique Daily Life Example: Refrigerator Operation

The refrigerator uses a refrigerant that absorbs heat (Q) from inside, then compresses, condenses, and releases heat outside. This process operates on a reversed Carnot cycle, transferring heat from a cooler interior to a warmer exterior, illustrating the second law of thermodynamics.

Equation involved: The refrigerant cycle involves work input (W) to transfer heat (Q_in) from the cold compartment to the hot outside environment.