Introduction to Thermodynamics

Overview of Thermodynamics

• Thermodynamics encompasses the study of energy concepts, applications, systems, surroundings, thermodynamic laws, and Gibbs free energy.

Concepts

• Thermodynamics focuses on interchanges of different energy forms.
• The first law of thermodynamics states that energy remains conserved, though it can interconvert into different forms. The sum of energy remains constant.
• According to the second law, the entropy of an isolated system consistently increases.
• The third law stipulates that the entropy of any pure, perfect crystal equals zero at 0 K (absolute zero).

Zeroth Law of Thermodynamics

• It relates to the temperature of a system.
• If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C will be in thermal equilibrium with object A.

Applications of Thermodynamics

• Thermodynamics applies to everything in daily life.
• It can calculate how many grams of ice one must melt using body heat to equal the calories gained from eating one gram of sucrose.
• It can determine the work done during muscle contraction or expansion.
• It is used to determine how chemical reactions can be harnessed to do work or produce heat.

Systems and Surroundings

• Treating energy and its conversion quantitatively involves defining systems and surroundings.
• A system constitutes part of the universe that one is interested in, like the Sun, Earth, a person, the liver, a single cell, or a mole of liquid water at 15°C and 1 atm pressure.
• Additionally, a system represents a matter quantity or a region in space chosen for study.
• Object boundaries of interest must be specified to differentiate system from surroundings; this allows for determining energy gain or loss.
• It's up to individual judgment to conceptually demarcate a system from its surroundings.

System, Surroundings, and Boundary

• The boundary between them can be fixed or movable.

Types of Systems

• Energy can be transferred between the system and surroundings, but the total energy of the system plus surroundings is constant.
• The change in energy of a system equals the amount of energy that entered from the surroundings minus the energy that went out into the surroundings.

Closed System

• Also known as Control Mass with a fixed amount of mass.
• It allows for energy exchange but does not permit matter exchange with the surroundings.
• It can be physically constructed by enclosing the system.
• Chemical reactions performed in closed systems that are stoppered flasks allow chemicals to stay inside while heat enters or leaves.
• Volume in a closed system doesn't have to be fixed necessarily.

Open System

• Also known as Control Volume.
• It's a properly selected arbitrary region in space.
• Both matter and energy can be exchanged with the surroundings.
• An example of an open system is a fertilized egg being hatched by a hen where O2 comes in, CO2 goes out, and heat is exchanged between the egg and its surroundings.

Isolated System

• This system consists of a special case where there is no energy and mass exchange with the surroundings.
• Constructing an isolated system is difficult.
• An insulated thermos is an imperfect but typical example of this system.

Properties of a System

• Any characteristic of a system is called a property.
• Familiar system properties like P, V, and T are called Variables of State.
• For a pure liquid, specifying P, V, and T sufficiently specifies many other liquid properties, such as density (ρ) and energy (E).

Variables of State

• Variables of State like P, V, and T help specify the state of a given system.
• Pressure (P) is measured in atm, Torr, or Pascals: 1 atm = 760 Torr = 1.01325 x 10^5 Pa.
• Volume (V) is measured in cm³, mL, L, quart, pint, or gallon.
• Temperature (T) is measured in °C, °F, or Kelvin (K): K = °C + 273.1 or K = (°F – 32) / 1.8 + 273.1.

Extensive and Intensive classes of variables state

• Extensive variable states depend on the size or extent of the system (e.g., m, V, E, and H).
• Intensive variable states are independent of the system size (e.g., P, T, ρ (density), μ (dynamic viscosity), and σ (surface tension)).

Extensive Properties

• Extensive ones are usually denoted by uppercase letters, except for mass (m).

Intensive Properties

• Intensive ones are usually denoted by lowercase letters, except for P and T.

Intensive Properties per unit mass are called specific properties

• Specific volume, v = V/m
• Specific energy, e = E/m

State

• If the system is not undergoing any change all properties can be measured and calculated resulting in set of properties called State which completely describes the condition.

Equilibrium

• Thermodynamics deals with equilibrium states.
• Equilibrium signifies a state of balance.
• Systems in equilibrium lack unbalanced potentials (or driving forces).
• Equilibrium systems experience no changes when isolated from their surroundings.
• Full thermodynamic equilibrium requires several types of equilibrium to be satisfied.

Types of Equilibrium

• Thermal Equilibrium: The temperature remains the same throughout the entire system (ΔT = 0), eliminating any driving force for heat flow.
• Mechanical Equilibrium: The pressure does not change over time at any point.
• Phase Equilibrium: Systems involving two phases achieve equilibrium when the mass of each phase reaches an equilibrium level and remains stable.
• Chemical Equilibrium: The chemical composition does not change with time, indicating that no chemical reactions are occurring.

Processes

• Any changes that a system undergoes from one equilibrium to another is called a process.
• A series of states through which a system passes during a process is called the PATH of a process.
• Describing a process involves specifying the initial and final states, the path followed, and the interaction with surroundings.

Quasi-Equilibrium

• A process proceeds in a manner where the system remains infinitesimally close to an equilibrium state at all times.
• It is a sufficiently slow process where the system adjusts internally so that properties at one part do not change faster than those at other parts.