Introduction to Thermodynamics

• Thermodynamics is the study of heat, temperature, and the inter-conversion of heat and other forms of energy.
• The behaviour of heat, temperature, and energy is governed by the four laws of thermodynamics.
• William Thomson coined the term thermodynamics in 1749.
• Thermodynamics explains how thermal energy converts to or from other forms of energy and how it affects matter.
• Thermal energy comes from heat, which is generated by the movement of tiny particles within an object. More movement = more heat.
• Thermodynamics focuses on the initial and final states of a system, not the rate of energy transformations.
• Thermodynamics is a macroscopic science, concerned with bulk systems rather than the molecular constitution of matter.
• Unlike mechanics, thermodynamics is not concerned with the motion of a system as a whole, but rather its internal macroscopic state.

Branches of Thermodynamics

• Classical thermodynamics analyses matter using a macroscopic approach, considering units like temperature and pressure to calculate other properties
• Statistical thermodynamics focuses on the properties and interactions of individual molecules to characterize the behaviour of a group of molecules.
• Chemical thermodynamics studies how work and heat relate to each other in chemical reactions and changes of state.
• Equilibrium thermodynamics studies transformations of energy and matter as they approach equilibrium.

Basic Concepts

• A thermodynamic system is a specific portion of matter with a defined boundary.
• The system boundary can be real or imaginary, fixed, or deformable.
• The surrounding is everything outside the system that directly influences its behaviour.
• A thermodynamic process occurs when there is energetic change within the system, associated with changes in pressure, volume, and internal energy.
• A thermodynamic cycle is a process (or combination of processes) where the initial and final states of the system are the same.
• At a given state, all properties of a system have fixed values.
• If one property changes, the system's state changes.
• In an equilibrium system, no changes in property values occur when isolated from its surroundings.
• A system is in thermodynamic equilibrium when it is in chemical, mechanical, and thermal equilibrium, and its relevant parameters cease to vary with time.

Thermodynamic Properties

• Thermodynamic properties, either extensive or intensive, define the state of a system.
• Enthalpy (H) is the measurement of energy in a thermodynamic system, equivalent to the system's internal energy (E) plus the product of its pressure (P) and volume (V): H = E + PV.
• Entropy is a thermodynamic quantity that depends on the physical state of a system, measuring its randomness or disorder.
• Thermodynamic potentials quantitatively measure stored energy in a system, reflecting energy changes as a system evolves from initial to final states under specific constraints like temperature and pressure.

Laws of Thermodynamics

• The laws of thermodynamics define fundamental physical quantities like energy, temperature, and entropy, and describe their behaviour under various conditions.
• There are four laws of thermodynamics.

Zeroth Law of Thermodynamics

• If two bodies are individually in equilibrium with a third body, then the first two bodies are also in thermal equilibrium with each other.
• This law enables the use of thermometers to compare the temperature of objects.

First Law of Thermodynamics

• Also known as the law of conservation of energy: energy can neither be created nor destroyed, but it can be changed from one form to another.

Second Law of Thermodynamics

• The entropy in an isolated system always increases, spontaneously evolving towards thermal equilibrium (the state of maximum entropy).
• The entropy of the universe only increases and never decreases.

Third Law of Thermodynamics

• The entropy of a system approaches a constant value as the temperature approaches absolute zero.
• The entropy of a pure, crystalline substance at absolute zero temperature is zero.

Applications of Thermodynamics

• Thermodynamics deals with the transfer of energy from one form to another.
• Laws of thermodynamics: zeroth, first, second, and third law.
• Entropy measures the number of possible arrangements of atoms in a system.
• Enthalpy measures energy in a thermodynamic system.
• The human body obeys the laws of thermodynamics.
• Sweating is the body's way of cooling itself, transferring heat to sweat, which then evaporates, increasing disorder and transferring heat to the air.