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# Second Law of Thermodynamics and Entropy Thermodynamics is the science relating temperature, heat, work and energy. The behaviour of these quantities is explained by the laws of thermodynamics. There are four laws of thermodynamics.

## Heat

Heat is the energy that can be transferred between substances when there is a temperature difference between them. Heat energy can be transferred to other forms of energy and vice versa. For example, heat energy is transferred to kinetic energy in a steam engine. Heat can be transferred between two bodies by conduction, convection and radiation.

### Temperature

Temperature is the physical quantity that expresses the hotness or coldness of a substance. The temperature of a substance can be measured using different scales.

### Specific Heat Capacity

The heat required to raise the temperature of a certain amount of a substance is called the specific heat capacity. Specific heat of the substance will depend on the number of atoms present in it, and not on the mass of the substance.

### Thermal Conductivity

The ability of a substance to transfer or conduct heat is called thermal conductivity. The rate at which heat flows through the substance is expressed as the amount of heat that flows per unit area, with a temperature gradient of one degree per unit distance.

### Entropy

Heat is wasted by all thermodynamic systems. The entropy of the closed system increases due to wasted heat. The entropy of the system always increases. Entropy can also be defined as the measure of the disorder or the randomness of the closed system.

### Four Laws of Thermodynamics

The fundamental principles of thermodynamics were expressed by three thermodynamic laws. Later it was found that the most fundamental law was neglected. The new law was called the Zeroth law of thermodynamics.

Zeroth Law of Thermodynamics: The zeroth law of thermodynamics states that, when two bodies are in thermal equilibrium with a third body, then they are in thermal equilibrium with each other.

First Law of Thermodynamics: The first law of thermodynamics states that the change in the internal energy of a system is equal to the heat added to the system minus the work done by the system. The first law is also called the law of conservation of energy, which states that energy cannot be created or destroyed in an isolated system.

Second Law of Thermodynamics: This law states that in a closed system, there is no process that will increase the net organization of the system. The second law of thermodynamics states that the entropy of the system increases, which means the universe is moving towards the state of complete randomness.

Third Law of Thermodynamics: The third law of thermodynamics states that the entropy of the system approaches a constant value as the temperature reaches absolute zero. The absolute zero is the lowest temperature that is physically possible.

Thermodynamics is science that was developed centuries ago and the principles of thermodynamics can be applied to every device that has been invented.