Short Answer
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. It is also known as the law of energy conservation. This principle applies to all thermodynamic processes, ensuring that the total energy of a system and its surroundings remains constant.
In thermodynamics, the First Law is expressed as:
Q=ΔU+WQ = \Delta U + WQ=ΔU+W
where Q is the heat added to the system, ΔU is the change in internal energy, and W is the work done by the system. This law is fundamental in analyzing engines, refrigerators, and heat transfer systems.
Detailed Explanation
Understanding the First Law of Thermodynamics
The First Law of Thermodynamics explains the relationship between heat, work, and internal energy in a system. It states that any heat energy supplied to a system is either used to increase its internal energy or converted into work.
Mathematical Expression
The First Law is given by the equation:
Q=ΔU+WQ = \Delta U + WQ=ΔU+W
Where:
- Q = Heat energy supplied to the system (Joules)
- ΔU = Change in internal energy of the system (Joules)
- W = Work done by the system (Joules)
This equation means:
- If heat is added to the system, it increases internal energy or is converted into work.
- If a system performs work, it loses internal energy unless heat is supplied.
Different Cases of the First Law
- When No Heat is Added (Adiabatic Process)
- Q = 0, so the equation becomes ΔU = -W.
- This means the internal energy decreases when work is done by the system.
- When No Work is Done (Isochoric Process)
- W = 0, so the equation simplifies to Q = ΔU.
- All the heat supplied increases internal energy.
- When Internal Energy is Constant (Cyclic Process)
- ΔU = 0, so the equation becomes Q = W.
- Heat added is completely converted into work.
Applications of the First Law
- Heat Engines
- Converts heat energy into mechanical work, as seen in car engines and power plants.
- Refrigeration and Air Conditioning
- Uses work to transfer heat from a cooler region to a hotter region.
- Boilers and Steam Turbines
- Heat is supplied to water, converted into steam, and used to perform mechanical work.
Conclusion
The First Law of Thermodynamics is the principle of energy conservation, stating that energy is neither created nor destroyed, only converted. It explains how heat energy is used to increase internal energy or perform work. This law is crucial for analyzing engines, refrigeration, and heat transfer systems in mechanical engineering.