Thermodynamics: Systems and Properties

• Thermodynamics is the study of energy, its transformations, and its relationship to matter
• Thermodynamics relies on universal laws applicable across various fields, including engineering, chemistry, and physics
• Thermodynamics aids in understanding and predicting the behavior of physical systems

Thermodynamic System

• A thermodynamic system is a specific region or quantity of matter under study
• The surroundings encompass everything outside the system
• A boundary separates the system from its surroundings

Types of Thermodynamic Systems

• Isolated systems exchange neither energy nor matter with the surroundings
• Closed systems exchange energy but not matter with the surroundings
• Open systems exchange both energy and matter with the surroundings

Macroscopic Properties of a System

• These properties can be intensive or extensive

Intensive Properties

• Intensive properties do not depend on the system's size

• Temperature (T) is an intensive property

• Pressure (P) is an intensive property

• Density $(\rho)$ is an intensive property

Extensive Properties

• Extensive properties depend on the system's size

• Mass (m) is an extensive property

• Volume (V) is an extensive property

• Energy (E) is an extensive property

Thermodynamic Equilibrium

• Thermodynamic equilibrium means a system is in thermal, mechanical, and chemical equilibrium

• Thermal equilibrium requires uniform temperature throughout the system

• Mechanical equilibrium requires uniform pressure throughout the system

• Chemical equilibrium means there is no change in chemical composition

Thermodynamic Process

• A thermodynamic process involves a change in the state of a system
• Isothermal processes occur at constant temperature
• Isobaric processes occur at constant pressure
• Isochoric processes occur at constant volume
• Adiabatic processes involve no heat exchange with the surroundings
• Cyclic processes return the system to its initial state

Equations of State

• These equations relate state variables (P, V, T) of a system

Ideal Gas Law

• Defined as: $PV = nRT$
• P represents pressure
• V represents volume
• n represents the number of moles
• R represents the ideal gas constant
• T represents temperature

Van der Waals Equation

• Defined as: $(P + a\frac{n^2}{V^2})(V - nb) = nRT$
• a and b are gas-specific constants

The Laws of Thermodynamics

Zeroth Law

• If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other

First Law

• The change in internal energy $(\Delta U)$ of a system equals the heat added (Q) minus the work done (W)
• Defined as: $\Delta U = Q - W$
• U represents internal energy
• Q represents heat added to the system
• W represents work done by the system

Second Law

• The total entropy of an isolated system can only increase or remain constant in ideal cases
• Defined as: $\Delta S \geq 0$
• S represents entropy

Third Law

• As temperature approaches absolute zero (0 K), the entropy of a system approaches a minimum or zero value