Thermodynamics: A Comprehensive One-Shot Review
Key Concepts: Thermodynamics, System, Surroundings, Universe, Open System, Closed System, Isolated System, State Variables, Extensive Properties, Intensive Properties, Isothermal Process, Isobaric Process, Isochoric Process, Adiabatic Process, State Function, Path Function, Internal Energy, Work Done.
Basic Terms in Thermodynamics
System and Surroundings
- System: The part of the universe under observation.
- Surroundings: The remaining part of the universe outside the system.
- Universe: System + Surroundings.
- Boundary: The separation between the system and surroundings.
Example: A reaction between A and B in a beaker is the system, and the room where the beaker is kept is the surrounding.
Types of Systems
- Open System: Exchange of both energy and matter with the surroundings.
- Closed System: Exchange of energy but not matter with the surroundings.
- Isolated System: No exchange of either energy or matter with the surroundings. A thermos flask is a basic example, though not perfectly isolated.
State Variables
- Parameters used to describe the equilibrium state of a system.
- Examples: Pressure (P), Volume (V), Temperature (T), Mass, Composition.
- State variables are not necessarily independent.
- Change in state function depends only upon initial and final condition.
Extensive and Intensive Properties
- Extensive Property: Depends on the amount of matter in the system (e.g., mass, volume, moles, internal energy).
- Intensive Property: Does not depend on the amount of matter in the system (e.g., pressure, temperature, molarity, density).
- The ratio of two extensive properties yields an intensive property (e.g., molarity = moles/volume).
Example: Concentration of sugar in a bottle is an intensive property; taking a small portion doesn't change the concentration.
Thermodynamic Processes
A process is defined by a change in a system, a passage from an initial state to a final state.
Isothermal Process
- Occurs at constant temperature (T = constant).
- Pressure and volume can change.
- Graph of pressure vs. volume shows a curve, indicating inverse relationship while temperature remains constant.
Isobaric Process
- Occurs at constant pressure (P = constant).
- Volume and temperature can change.
- Work done in an isobaric process is related to the pressure and change in volume.
Isochoric Process
- Occurs at constant volume (V = constant).
- Pressure and temperature can change.
- Work done in an isochoric process is zero because there is no change in volume.
Adiabatic Process
- No heat exchange with the surroundings (Q = constant or ΔQ = 0).
- Pressure and volume can change.
- Adiabatic walls prevent heat transfer but allow work.
- Graph of pressure vs. volume shows a curve, indicating changes in both variables without heat exchange.
Example: Water in a thermos flask approximates an adiabatic system.
State of a System
- State Function: A property that depends only on the initial and final states of the system, not on the path taken (e.g., pressure, volume, temperature).
- Path Function: A property that depends on the path taken to reach a specific value (e.g., work, heat).
Key Point: Heat and work are path functions.
- Cyclic Process: A process where the system returns to its initial state. The change in state function for a cyclic process is zero.
Energy and Work Done
- Internal Energy (U): The total energy stored within a system, including potential and kinetic energy. It is a state function.
- Change in internal energy (ΔU) can occur through heat exchange, work, or matter transfer.
- If ΔU is negative, energy is released from the system. If ΔU is positive, energy is absorbed by the system.
- For an isothermal process, ΔU = 0 because the temperature is constant.
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