Thermodynamics Laws

• Thermodynamics is the study of energy, its transformations, and its relation to matter

Laws of Thermodynamics

• The laws of thermodynamics govern the behavior of energy and matter at a macroscopic level

Zeroth Law

• If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other
• This law implies the existence of a common property, temperature, that determines whether two systems are in thermal equilibrium

First Law

• Energy cannot be created or destroyed, only converted from one form to another
• The change in internal energy of a system (ΔU) is equal to the heat added to the system (Q) minus the work done by the system (W): ΔU = Q - W
• This law introduces the concept of internal energy (U) as a state function

Second Law

• The total entropy of an isolated system can only increase over time or remain constant in ideal cases
• Entropy is a measure of the disorder or randomness of a system
• Heat cannot spontaneously flow from a cold body to a hot body without external work being performed on the system
• This law introduces the concept of entropy (S) and implies the irreversibility of natural processes

Third Law

• As the temperature of a system approaches absolute zero (0 Kelvin), the entropy approaches a minimum or zero value
• This law provides a reference point for determining entropy

Thermodynamic Cycles

• A thermodynamic cycle is a series of thermodynamic processes that returns a system to its initial state
• During a cycle, work can be done by or on the system, and heat can be added or removed
• Cycles are fundamental to the operation of heat engines, refrigerators, and heat pumps

Carnot Cycle

• The Carnot cycle is a theoretical thermodynamic cycle with the highest possible efficiency
• It consists of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression
• The efficiency of a Carnot cycle depends only on the temperatures of the hot and cold reservoirs: η_Carnot = 1 - (T_cold / T_hot)

Otto Cycle

• The Otto cycle is an idealized thermodynamic cycle that describes the operation of a typical spark-ignition internal combustion engine
• It consists of four processes: adiabatic compression, constant-volume heat addition, adiabatic expansion, and constant-volume heat rejection

Diesel Cycle

• The Diesel cycle is an idealized thermodynamic cycle that describes the operation of a compression-ignition internal combustion engine
• It consists of four processes: adiabatic compression, constant-pressure heat addition, adiabatic expansion, and constant-volume heat rejection

Rankine Cycle

• The Rankine cycle is a thermodynamic cycle that converts heat into work, commonly used in steam power plants
• It consists of four processes: pumping, boiling, expansion, and condensation

Heat Engines

• A heat engine is a device that converts thermal energy into mechanical work
• It operates by transferring heat from a high-temperature reservoir to a low-temperature reservoir and converting a portion of that heat into work
• The efficiency of a heat engine is defined as the ratio of the work output to the heat input: η = W / Q_hot

Types of Heat Engines

• Internal combustion engines (e.g., gasoline and diesel engines)
• External combustion engines (e.g., steam engines)
• Gas turbines
• Jet engines

Entropy

• Entropy (S) is a measure of the disorder or randomness of a system
• It is a state function, meaning its value depends only on the current state of the system, not on how it reached that state
• Entropy is related to the number of possible microstates (Ω) corresponding to a given macrostate, as described by the Boltzmann equation: S = k_B ln(Ω), where k_B is the Boltzmann constant

Entropy Change

• The change in entropy (ΔS) for a reversible process is given by: ΔS = Q_rev / T, where Q_rev is the heat transferred reversibly and T is the absolute temperature
• For irreversible processes, the entropy change is greater than Q / T: ΔS > Q / T

Entropy and the Second Law

• The second law of thermodynamics states that the total entropy of an isolated system can only increase or remain constant in a reversible process
• This implies that spontaneous processes tend to increase the disorder or randomness of the system
• The increase in entropy is a measure of the energy that is no longer available to do work

Statistical Interpretation of Entropy

• Entropy can be interpreted as a measure of the uncertainty or lack of information about the microscopic configuration of a system
• A high-entropy state corresponds to a large number of possible microstates, making it difficult to predict the exact state of the system

Phase Transitions

• A phase transition is a physical process in which a substance changes from one state of matter to another
• Common phases of matter include solid, liquid, and gas, as well as plasma and Bose-Einstein condensate
• Phase transitions are accompanied by changes in thermodynamic properties such as temperature, pressure, and entropy

Types of Phase Transitions

• Melting/Freezing: Solid to liquid or liquid to solid
• Vaporization/Condensation: Liquid to gas or gas to liquid
• Sublimation/Deposition: Solid to gas or gas to solid
• Triple Point: The temperature and pressure at which three phases of a substance coexist in equilibrium
• Critical Point: The temperature and pressure at which the distinction between liquid and gas phases disappears

Latent Heat

• Latent heat is the heat absorbed or released during a phase transition at a constant temperature
• It is the energy required to change the phase of a substance without changing its temperature
• Latent heat of fusion is associated with melting or freezing, while latent heat of vaporization is associated with vaporization or condensation

Phase Diagrams

• A phase diagram is a graphical representation of the equilibrium conditions for different phases of a substance
• It shows the temperature and pressure at which phase transitions occur
• Phase diagrams are useful for predicting the phase of a substance under different conditions

Clausius-Clapeyron Equation

• The Clausius-Clapeyron equation relates the change in pressure with temperature during a phase transition to the enthalpy and volume changes
• dP/dT = ΔH / (TΔV), where P is pressure, T is temperature, ΔH is the enthalpy change, and ΔV is the volume change
• This equation can be used to predict how the vapor pressure of a substance changes with temperature