Thermodynamics

Thermodynamics is a set of physical laws. These laws will govern the random statistical behavior of some number of atoms in a physical system. This is the kind of energy and motion of heat. These are the laws of thermodynamics: they are laws of heat.

Sadi Carnot is considered by many to be the father of thermodynamics. His 1824 publication was the first successful theory of heat engines. It was later used to establish the laws of entropy. Carnot explained how heat engines worked. He also explained how heat can cause motion. He referred to this as motive power. This led to the idea of the Carnot cycle. His idea was that the most efficient way to extract heat for this motive power was by cycling the temperature and pressure of a gas. This eventually paved way to the internal combustion engine.

Carnot relied on the caloric theory of heat. This was the incorrect notion that heat is a physical substance. By the 1830s, Carnot had accepted that heat is a consequence of the movement of particles. The faster particles are moving, the hotter the substance. This is known as the dynamic theory of heat.

Laws of thermodynamics

There are 4 laws of thermodynamics that define properties that a system in thermodynamic equilibrium will have, such as temperature, entropy and energy. A pair of systems are in thermodynamic equilibrium, if, no heat flows between them. One system can be in thermodynamic equilibrium with itself, if heat is uniformly distributed throughout the system.

0. If two thermodynamic systems are in equilibrium to another third system, they will all be in thermodynamic equilibrium with each other.

1. Energy cannot be created or destroyed.

2. The total entropy of an isolated system increases with time.

3. There is a minimum temperature, at which, the motion of the particles of matter would cease.

0. The "zeroth" law of thermodynamics, states that:

If two systems are in thermodynamic equilibrium with a third, than they are in thermodynamic equilibrium with each other.
This helps define the notion of temperature, since, all three of these systems, would be the same temperature.
The physical implication for this law is that temperature is a measurable physical quantity.

1. The first law of thermodynamics, states that:

Energy, can be transformed, from one state to another, however, it cannot be created or destroyed.
Thus, perpetual motion machines, of the first kind, which produce work with no energy input, are not possible.

Quote from Arthur Eddington on the 2nd law of thermodynamics.

2. The second law of thermodynamics, states that:

Naturally, in thermodynamic properties, entropy always increases.
The total entropy for an isolated system can never decrease with time. It can increase, and in some cases stay the same, however, never decrease.
Thus, perpetual motion machines of the 2nd kind, which spontaneously converts thermal energy into mechanical work, is not possible.

3. The third law of thermodynamics, states that:

The entropy of objects at absolute zero temperature, is a constant value. It is typically close to zero, however, it is not necessarily zero.

Entropy

There is also a property of physical systems, in the 2nd law of thermodynamics, called entropy, that increases with time. Entropy is hidden information. The entropy of an isolated system can never decrease with time. This law of entropy increase is known as the 2nd law of thermodynamics. Entropy is related to randomness. It is the measure of disorder in a physical system. As the entropy of a system increases, it becomes more and more random. Indeed, entropy measures the degree of disorder of a physical system. A measure of entropy will be the number of different microscopic configurations that a physical system can undergo that can still lead to the same macroscopic properties. Another way to think about entropy is that it is the number of ways you can change the distribution of atoms and molecules in a region of space, without changing the macroscopic properties of the system as a whole. The larger the entropy, the more ways the atoms and molecules can be configured and reconfigured, without changing the macroscopic appearance of the physical system. When a system has the maximum possible amount of entropy, it can said to be in thermal equilibrium.

Ludwig Boltzman

Ludwig Boltzmann, an Austrian physicists, who contributed greatly to the discovery of statistical mechanics, is going to carefully look at this concept in the 1870s. What Boltzman demonstrated was that the thermodynamic properties of a gas, could be understood by averaging properties of its constituent molecules. This process of “averaging” led to the ability to understand various properties, such as temperature and pressure.

Newton's laws of motion, however, says that the laws of physics are reversible. Thus, there cannot be a quantity that always increases. What is entropy then? What is the meaning of the 2nd law of thermodynamics? Entropy, according to Boltzmann, is hidden information. Information is hidden, contained in degrees of freedom that are to small and too numerous.

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