Laws of Thermodynamics

Before we dive into the Laws of Thermodynamics, there are some key definitions and concepts that we must understand.  These are given below.  System and Surroundings In order to avoid confusion, scientists discuss thermodynamic values in reference to a system and its surroundings. Everything that is not a part of the system constitutes its surroundings. The system and surroundings are separated by a boundary. If matter is not able to pass across the boundary, then the system is said to be closed; otherwise, it is open. For example, if the system is one mole of a gas in a container, then the boundary is simply the inner wall of the container itself. Everything outside of the boundary is considered the surroundings, which would include the container itself. Thermodynamic States:  The application of thermodynamic principles begins by defining a system that is in some sense distinct from its surroundings.  For example, the system could be a sample of gas inside a cy...

What is the Zeroth Law of Thermodynamics? The zeroth law of thermodynamics states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. The physical meaning is expressed by Maxwell in the words: " All heat is of the same kind ". As an illustration, suppose we have three objects as shown on the slide. Object A and Object B are in physical contact and in thermal equilibrium. Object B is also in thermal equilibrium with Object C. There is initially no physical contact between Object A and Object C. But, if Object A and Object C are brought into contact, it is observed that they are in thermal equilibrium Background of the Zeroth Law The zeroth law was first formulated and labelled by R. H. Fowler in 1931.  As the name suggests, its value as a fundamental physical principle was recognized more than half a century after the formulation of the first and the second laws of thermodynamics. It was named the zeroth law si...

What is the First Law of Thermodynamics? The first law of thermodynamics is simply an expression of the conservation  of energy principle, and it asserts that energy is a thermodynamic  property. The first law of thermodynamics defines the internal energy (E) as equal to the difference of the heat transfer (Q) into a system and the work (W) done by the system. E2 - E1 = Q - W Here the words heat transfer into a system and work done by the system are important as they define the sign convention. Heat removed from a system would be assigned a negative sign in the equation. Similarly work done on the system is assigned a negative sign. The First Law of Thermodynamics. The energy change of a system during a process is equal to the net work and heat transfer between the system and its surroundings. Applications of the First Law of Thermodynamics As mentioned above, the first law of thermodynamics is a generalization of the law of conservation of energy, which states that en...

What is the Second Law of Thermodynamics? The Second Law of Thermodynamics, also known as the Law of Increased Entropy, says that over time the state of disorganization or entropy in a system will always increase.  Over time, usable energy will eventually give way to unusable energy. While energy cannot be created or destroyed according to the First Law, it can change form a useful state to a less-useful state, like thermal energy (heat). For example, as you read this article, entropy is all around you. Cells within your body are dying and degrading, an employee or coworker is making a mistake, the floor is getting dusty, and the heat from your coffee is spreading out. Zoom out a little, and businesses are failing, crimes and revolutions are occurring, and relationships are ending. Zoom out a lot further, and we see the entire universe marching towards a collapse. The Discovery of Entropy The identification of entropy is attributed to Rudolf Clausius (1822–1888), a German mathemati...

What is the Third Law of Thermodynamics? The third law of thermodynamics states that the entropy of a perfect crystal at a temperature of zero Kelvin (absolute zero) is equal to zero. Entropy, denoted by ‘S’, is a measure of the disorder/randomness in a closed system. It is directly related to the number of microstates (a fixed microscopic state that can be occupied by a system) accessible by the system, i.e. the greater the number of microstates the closed system can occupy, the greater its entropy. The microstate in which the energy of the system is at its minimum is called the ground state of the system. At a temperature of zero Kelvin, the following phenomena can be observed in a closed system: The system does not contain any heat. All the atoms and molecules in the system are at their lowest energy points. Therefore, a system at absolute zero has only one accessible microstate – it’s ground state. As per the third law of thermodynamics, the entropy of such a system is exa...

Conclusion With this we’ve summarized the basics behind the Laws of Thermodynamics. This blog has but just scratched the surface, and there’s a lot of exciting science both to be learned and discovered in this field.  Thermodynamics is a very important field of study as it has implications from the machines we use to the internal machines that run in our bodies. It can be used to build more efficient engines and other stuff in the domains of physics. It can be used to discover new spontaneous reactions, create better chemicals, and improve methods of production of various industrial chemicals, by increasing energy efficiency.  Thermodynamic topics such as Gibbs Free Energy and Enthalpy, become important in biochemistry, especially in understanding the importance of enzymes, and why certain biochemical pathways and various catabolic and anabolic reactions take place in living systems. Thermodynamics is truly a robust and important field of study, with implications and applicati...