In thermodynamics, energy and work are fundamental concepts that describe how systems exchange energy with their surroundings and undergo changes.
Contents:
Energy in Thermodynamics
Definition: Energy is the capacity of a system to do work or transfer heat. It can exist in various forms, such as internal energy, kinetic energy, potential energy, thermal energy, etc.
Forms of Energy in a System:
Internal Energy (U): The total energy within a system due to molecular motion and interactions.
Kinetic Energy (KE): Energy due to the motion of the system as a whole.
Potential Energy (PE): Energy stored due to position or configuration.
Conservation of Energy: The First Law of Thermodynamics states that energy can neither be created nor destroyed; it can only change forms or be transferred.
Mathematically:
ΔU=Q−W
where:
ΔU: Change in internal energy.
Q: Heat added to the system.
W: Work done by the system.
Work in Thermodynamics
Definition: Work is the energy transferred when a force is applied to a system, causing a displacement, or when a system changes its volume under pressure.
Work Formula: For pressure-volume work (common in thermodynamic systems):
W=PΔV.
Where :
P: Pressure (constant in some cases).
ΔV: Change in volume of the system.
Sign Convention:
W>0: Work done by the system on the surroundings (e.g., gas expansion).
W<0: Work done on the system by the surroundings (e.g., gas compression).
Key Differences
| Aspect | Energy | Work |
|---|---|---|
| Nature | Capacity to do work or transfer heat. | Transfer of energy by force or volume change. |
| Form | Stored in a system (internal, kinetic, etc.). | Always in transit; not stored. |
| Measurement | State function (depends only on the state). | Path function (depends on the process). |
Example:
- A gas expands in a piston:
- Energy: The system loses internal energy as heat and work.
- Work: The gas does work on the piston as it pushes against it, causing displacement.
In summary, energy is a system’s ability to perform tasks, while work is one way energy is transferred during a process.
Also Read:
- Types of Energy.
- Heat transfer mechanism.