Thermodynamics Basics

Thermodynamics

• Definition: Branch of physics focusing on heat, work, temperature, and energy.

• Basic Concepts:

  • System: The part of the universe under study (can be open, closed, or isolated).
  • Surroundings: Everything outside the system.
  • State Functions: Properties that depend only on the state of the system (e.g., temperature, pressure, volume).

• Laws of Thermodynamics:

  1. Zeroth Law: If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
  2. First Law: Energy cannot be created or destroyed, only transferred or changed in form. (\Delta U = Q - W) (Change in internal energy = heat added - work done by the system).
  3. Second Law: The total entropy of an isolated system can never decrease over time. Heat naturally flows from hot to cold, and processes occur in a direction that increases the total entropy.
  4. Third Law: As the temperature of a system approaches absolute zero, the entropy approaches a constant minimum.

• Key Terms:

  • Heat (Q): Energy transferred due to temperature difference.
  • Work (W): Energy transfer that occurs when a force is exerted over a distance.
  • Internal Energy (U): Total energy contained within a system.
  • Enthalpy (H): Total heat content of a system; (H = U + PV) (Pressure (\times) Volume).
  • Entropy (S): Measure of disorder or randomness in a system.

• Processes:

  • Isothermal: Constant temperature (Q = W).
  • Adiabatic: No heat exchange with surroundings (Q = 0).
  • Isochoric: Constant volume (W = 0, (\Delta U = Q)).
  • Isobaric: Constant pressure (Q = ΔH).

• Applications:

  • Heat Engines: Convert heat into work, operating on cyclic processes (Carnot cycle is an idealized example).
  • Refrigerators and Heat Pumps: Transfer heat against its natural flow, requiring work input.

• Thermodynamic Cycles:

  • Carnot Cycle: Theoretical cycle showing maximum efficiency possible for a heat engine.
  • Otto Cycle: Used in gasoline engines; describes the processes of compression and expansion.
  • Diesel Cycle: Similar to Otto but with continuous combustion.

• Critical Points:

  • Phase Transitions: Points at which a substance changes from one state of matter to another, such as melting or boiling.
  • Critical Point: The end point of phase equilibrium between liquid and gas.

• Equations of State:

  • Ideal Gas Law: (PV = nRT) (Pressure (\times) Volume = Moles (\times) Ideal Gas Constant (\times) Temperature).
  • Van der Waals Equation: Adjusts ideal gas law to account for non-ideal behavior of real gases.

• Specific Heat: Amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius.

Understanding these fundamental principles is crucial for assessing energy interactions, heat flow, and the behavior of materials under various conditions in thermodynamics.

Thermodynamics

• Definition: The study of how heat, work, temperature, and energy are related.
• Basic Concepts:
  • System: The part of the universe being studied.
  • Surroundings: Everything outside the system.
  • State Functions: Properties of a system that depend only on its current state, not its history (e.g., temperature, pressure, volume).
• Laws of Thermodynamics:
  • Zeroth Law: If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
  • First Law: Energy cannot be created or destroyed, only transferred or transformed. This is expressed as: (ΔU = Q - W) (Change in internal energy = heat added - work done by the system).
  • Second Law: The total entropy of an isolated system can never decrease over time. Heat flows naturally from hot to cold, and processes occur in a way that increases the total entropy.
  • Third Law: As the temperature of a system approaches absolute zero, the entropy approaches a constant minimum.
• Key Terms:
  • Heat (Q): Energy transferred due to a temperature difference.
  • Work (W): Energy transferred when a force is exerted over a distance.
  • Internal Energy (U): The total energy contained within a system.
  • Enthalpy (H): The total heat content of a system, defined as (H = U + PV) (Pressure (\times) Volume).
  • Entropy (S): A measure of disorder or randomness in a system.

Processes

• Isothermal: A process that occurs at a constant temperature (Q = W).
• Adiabatic: A process where no heat is exchanged with the surroundings ( Q = 0).
• Isochoric: A process that occurs at constant volume (W = 0, (\Delta U = Q)).
• Isobaric: A process that occurs at constant pressure (Q = ΔH).

Applications

• Heat Engines: Devices that convert heat into work, operating on cyclic processes. The Carnot cycle is a theoretical model for maximum efficiency.
• Refrigerators and Heat Pumps: Devices that transfer heat against its natural flow, requiring input of work.

Thermodynamic Cycles

• Carnot Cycle: A theoretical thermodynamic cycle that represents the maximum efficiency possible for a heat engine.
• Otto Cycle: A thermodynamic cycle used in gasoline engines, describing the processes of compression and expansion.
• Diesel Cycle: Similar to the Otto cycle, but with continuous combustion during the power stroke.

Critical Points

• Phase Transitions: Points at which a substance changes from one state of matter to another, such as melting or boiling.
• Critical Point: The end point of phase equilibrium between liquid and gas.

Equations of State

• Ideal Gas Law: (PV = nRT) (Pressure (\times) Volume = Moles (\times) Ideal Gas Constant (\times) Temperature).
• Van der Waals Equation: An equation that adjusts the ideal gas law to account for the non-ideal behavior of real gases.
• Specific Heat: The amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius.