Thermodynamics Fundamentals: Systems, Processes, and Equilibrium

Thermodynamics Essentials

Thermodynamics is the science that studies the work and heat exchange between a system and its environment.

First Law

This law states that the amount of energy in any system remains constant; it can only be transformed.

Systems

System

A system is an amount of material chosen for study.

Closed System

A closed system has no exchange of mass, only energy exchange.

Isolated System

An isolated system has no exchange of energy or mass.

Open System

An open system has energy and mass exchange between the environment and the system.

Surroundings

The surroundings are the region outside the system.

Boundary

The boundary is the surface separating the system from its surroundings.

Processes

A process is any change that a system experiences from one equilibrium state to another.

Path

A path is a series of states the system passes through during a process.

Properties

Properties are variables used to describe the state of a system.

• Intensive variables do not depend on the size of a system, such as temperature, pressure, and density.
• Extensive variables depend on the size of the system.

Types of Processes

• Isothermal: The temperature of the system remains constant.
• Isobaric: The system pressure is constant.
• Isometric: The volume remains constant.
• Adiabatic: There is no heat transfer.
• Quasistatic: Allows an internal adjustment.

Equilibrium

Equilibrium is a state of balance.

Thermal Equilibrium

Thermal equilibrium occurs when the temperature is the same throughout the system.

Mechanical Equilibrium

Mechanical equilibrium occurs when there is no change in pressure at any point in the system.

Phase Equilibrium

Phase equilibrium occurs when the mass of each phase reaches an equilibrium level.

Chemical Equilibrium

Chemical equilibrium occurs when the chemical composition does not change with time.

Key Concepts

Energy: The capacity to do work (light, heat, electricity).

Pressure: Force exerted by a fluid per unit area.

Zeroth Law

This law is based on the temperature of bodies. If bodies with different temperatures are put into contact, they eventually reach the same temperature.

Pure Substances

A pure substance has a fixed chemical composition.

One or more pure substances can form a homogeneous mixture.

Saturation

Saturation Temperature

Saturation temperature is the temperature at which a substance changes phase at a certain pressure.

Saturation Pressure

Saturation pressure is the pressure at which a substance changes phase at a given temperature.