In thermodynamics, heat and work are two fundamental forms of energy transfer between a system and its surroundings, and they play a central role in understanding energy transformations.
Let discuss in brief about these two concepts.
Heat (Q):
- Definition: Heat is the transfer of thermal energy between a system and its surroundings due to a temperature difference.
- Characteristics:
- Mechanism: Heat flows spontaneously from a region of higher temperature to a region of lower temperature.
- Microscopic Basis: It arises from the random motion of molecules or particles (kinetic energy) in the system.
- Sign Convention:
- Positive (+): Heat is added to the system (energy enters the system).
- Negative (−): Heat is removed from the system (energy leaves the system).
- Unit: Joules (J) in the SI system.
- Example: Heating water in a kettle involves transferring thermal energy from the stove to the water.
Work (W):
- Definition: Work is the energy transfer that occurs when a force is applied to a system and results in a displacement or change in volume.
- Characteristics:
- Mechanism: Work can occur when a system expands or contracts (e.g., moving a piston in an engine) or when external forces are applied.
- Microscopic Basis: It involves organized motion of molecules or particles (as opposed to random motion for heat).
- Sign Convention:
- Positive (+): Work is done on the system (energy enters the system).
- Negative (−): Work is done by the system (energy leaves the system).
- Unit: Joules (J) in the SI system.
- Example: Compressing a gas inside a piston involves doing work on the gas.
In first law of thermodynamics, the equation defines the relationship between Heat and Work in a system
The equation is,
ΔU=Q−W
Where,
ΔU = Internal energy of the system.
Q = Heat added to the system.
W = Work done by the system.
Also Read :
- Zeroth Law of Thermodynamics.
- First Law of Thermodynamics.
- Second Law of Thermodynamics.
- Third Law of Thermodynamics.