Introduction to Thermodynamics

Introduction to Thermodynamics

• Thermodynamics is the part of physics dedicated to the transformation of heat into work.
• Energy exists in various forms including light, heat, mechanical, gravitational, and nuclear.
• The goal of thermodynamics is to understand the relationships between different energy forms.

Thermodynamics Laws

• Zeroth Law: Defines temperature. Allows for the comparison of temperatures between systems.
• First Law: Conservation of energy. Energy can be neither created nor destroyed, only transformed.
• Second Law: Defines entropy. Quantifies the direction of spontaneous processes.
• Third Law: Relates entropy to the order of systems.

System and Surroundings

• A system is a portion of the universe under study.
• Surroundings are the rest of the universe outside the system.
• Systems are separated from the surroundings by a boundary.
• Systems exchange heat, work, and matter with their surroundings through the boundary.
• Systems can be described microscopically (atomic/molecular level) or macroscopically (using measurable properties).

System Classification

• Isolated: No energy (heat/work) or matter exchange with the surroundings. (e.g., Thermos)
• Closed: Energy (heat/work) exchange but no matter exchange. (e.g., Closed bottle)
• Open: Energy (heat/work) and matter exchange. (e.g., Open bottle)

Homogeneous and Inhomogeneous Systems

• Homogeneous: Uniform composition and a single phase. (e.g., Liquid)
• Inhomogeneous: Multiple phases or varying composition. (e.g., Liquid and gas)

Physical Quantities

• Intensive: Independent of system size or amount of matter. (e.g., Temperature, Pressure, Density)
• Extensive: Dependent on system size or matter amount. (e.g., Energy, Entropy, Mass).
• Extensive quantities can be transformed into intensive quantities by dividing by volume.

State Variables, State Functions, and State Equations

• State variables: Properties that can be measured experimentally, used to characterize a system's state (e.g., Pressure, Temperature, Volume).
• State functions: Parameters characterizing the system's state, but not directly measurable, they can be expressed in terms of state variables. (e.g., Internal Energy, Enthalpy, Gibbs Function, Free Energy).
• Examples for an ideal gas: U=U(T)
• State equation: Mathematical equations relating state variables, describing the system's state. (e.g., Ideal gas law: PV=nRT).
• Heat and work are not state functions or variables.

Ideal Gas

• A system of particles (molecules) that do not interact. Collisions are elastic.
• Ideal Gas Law: PV = nRT, where P is pressure, V is volume, n is number of moles, R is the gas constant, and T is temperature (in Kelvin).
• The ideal gas law is verified as a limit of the general gas law.
• Avogadro's law: At the same P, T, V all gases have the same number of moles.

Equilibrium States

• Systems are in thermodynamic equilibrium when there is no tendency for spontaneous change.
• Types of equilibrium: Mechanical, thermal, phase, and chemical.

Processes

• A process is a change in a system's state.
• Quasi-static: Processes that occur infinitely slowly to maintain equilibrium at each step. Intermediate states are equilibrium states.
• Non-static: The intermediate states are not equilibrium states.
• Reversible: A quasi-static process that can return the system to its initial state by reversing the process. The system goes through the same intermediate states in reverse order.
• Irreversible: A process that cannot be reversed to its original state through the same process.

Types of processes (at constant parameter)

• Isobaric: Constant pressure
• Isochoric: Constant volume
• **Isothermal:**Constant temperature
• Adiabatic: No heat transfer

Work

• Work done on a particle is force times distance.

• Thermodynamic work is related to work done by external forces on the system.

• The sign convention is used to indicate the direction of energy transfer. Positive work happens when the system gains energy and negative work happens when the system loses energy.

• Work is calculated as the integral of pressure with respect to change in volume, $W = \int{PdV}$.

Pressure

• Pressure is force per unit area.
• Atmospheric pressure
• Units of pressure (SI & CGS)
• Absolute pressure vs. Gauge pressure vs. Manometric pressure vs. Vacuum pressure

Manometer

• Used to measure pressure differences, including atmospheric pressure.
• Calculation of pressure using barometer and manometer

Processes Representation (P-V Diagrams)

• Graphical representation of processes.
• Show relationship between pressure and volume as processes occur.

Temperature

• Related to the kinetic energy of particles.
• Intensive property, identical throughout the system in thermal equilibrium.
• Zeroth law of thermodynamics
• Different scales (Celsius, Fahrenheit, Kelvin).

Thermometry

• Tools for measuring temperature, based on a thermometric property.
• Examples (ideal gas, liquid, metallic rod)
• Important properties of thermometric properties
• Reproducibility of the measurements

Thermal Coefficients

• Thermal expansion (linear coefficient)
• Volume coefficients
• Other thermal coefficients of compressibility
• Piezothermal coefficient.

Water Expansion

• Water's unusual behavior regarding temperature and density.
• Specific case between 0-4 °C