The Laws of Thermodynamics – Exam Guide
Intro to Thermodynamics
Thermodynamics is the branch of physics that deals with energy, heat, and work, along with their
interactions within physical systems. The fundamental laws of thermodynamics govern energy
conservation, entropy, and absolute zero, playing a crucial role in physics, chemistry, and engineering.
These laws explain how energy flows, why certain processes occur naturally, and why perpetual motion
machines are impossible.
The Four Laws of Thermodynamics
Although they are traditionally numbered as the first, second, and third laws, there is also a zeroth
law, which provides the foundation for temperature measurement.
Zeroth Law of Thermodynamics: Thermal Equilibrium
Definition:
If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other
Just know that :
• This law forms the basis of temperature measurement.
• It establishes temperature as a fundamental physical quantity, leading to the development of thermometers.
• It explains why heat naturally flows from a hotter object to a cooler one until both reach the same temperature.
First Law of Thermodynamics: Conservation of Energy
Definition:
Energy cannot be created or destroyed; it can only be transferred or transformed. The total energy of a closed system
remains constant.
• ΔU = Change in internal energy
• Q = Heat added to the system (+Q if absorbed, -Q if released)
• W = Work done by the system (+W if the system does work, -W if work is done on the system)
Keep in mind :
• Heat added to a system increases its internal energy or is used to do work
• If a system does work on its surroundings, its internal energy decreases
• If work is done on the system, its internal energy increases.
• This law applies to closed systems, where energy is exchanged but matter is not
Examples:
1. Compression of a Gas:
• Work is done on the gas (+W), increasing its internal energy (ΔU)
2. Expansion of a Gas:
• The gas does work on its surroundings (-W), decreasing ΔU
Intro to Thermodynamics
Thermodynamics is the branch of physics that deals with energy, heat, and work, along with their
interactions within physical systems. The fundamental laws of thermodynamics govern energy
conservation, entropy, and absolute zero, playing a crucial role in physics, chemistry, and engineering.
These laws explain how energy flows, why certain processes occur naturally, and why perpetual motion
machines are impossible.
The Four Laws of Thermodynamics
Although they are traditionally numbered as the first, second, and third laws, there is also a zeroth
law, which provides the foundation for temperature measurement.
Zeroth Law of Thermodynamics: Thermal Equilibrium
Definition:
If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other
Just know that :
• This law forms the basis of temperature measurement.
• It establishes temperature as a fundamental physical quantity, leading to the development of thermometers.
• It explains why heat naturally flows from a hotter object to a cooler one until both reach the same temperature.
First Law of Thermodynamics: Conservation of Energy
Definition:
Energy cannot be created or destroyed; it can only be transferred or transformed. The total energy of a closed system
remains constant.
• ΔU = Change in internal energy
• Q = Heat added to the system (+Q if absorbed, -Q if released)
• W = Work done by the system (+W if the system does work, -W if work is done on the system)
Keep in mind :
• Heat added to a system increases its internal energy or is used to do work
• If a system does work on its surroundings, its internal energy decreases
• If work is done on the system, its internal energy increases.
• This law applies to closed systems, where energy is exchanged but matter is not
Examples:
1. Compression of a Gas:
• Work is done on the gas (+W), increasing its internal energy (ΔU)
2. Expansion of a Gas:
• The gas does work on its surroundings (-W), decreasing ΔU
