Thermodynamics is a term familiar to all but not known by many. Surprisingly, this seemingly complicated word has a rather simple meaning: It is the study of heat, work done and temperature and how they are linked to the energy and entropy of a system.
Thermodyanmics is an entire branch of Physics built on eight schools of thought (based on the scientist who created it). What I’ll discuss in this Physics Rants is Classical Thermodynamics, ie the basic laws that nearly all of these schools can agree upon with utmost certainty.
Do note that in this Physics Rant, the Laws of Thermodyanmics will be a gross oversimplification to make understanding the complex processes more simple (Apologies Physics Nerds).
Zeroth Law- If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
First Law- The total energy of an isolated system is constant. Energy can be transferred in and out via heat and work but cannot be created or destroyed. It is represented Mathematically as (Where Delta U is change in Internal Energy, Q is Heat Added and W is Work done by system)
- \(\Delta U = Q - W\)
Second Law- In a closed system, the entropy (the amount of disorder in a system) can only increase or remain constant over time.
Explains the directions of thermal processes and the inefficiency of thermal conversions.
This can be expressed by the Kelvin-Planck Statement- It is impossible for any device that operates in a cycle to receive heat from a single reservoir and produce work
Or the Clausius Statement- Heat cannot spontaneously flow from a colder to a hotter body
Third Law- As the temperature of a system approaches absolute zero, the entropy of the system approaches a minimum (nominally zero)
This is a quick rundown of the Thermodynamic laws, now onto their respective applications:
Thermodynamics Cycles are in essence, transfers which involve heat and work transfers and aim to return a system to its initial state. The prime example is the Carnot cycle which aims to provide the maximum possible efficiency for a heat engine along with other notable ones like the Rankine, Otto and Diesel Cycles.
It can applied to determine equilibria as well, Thermodynamics finds use in useful functions used to derive enthalpy, Helmholtz free energy and Gibbs Free Energy. This mostly finds use in the context of chemical bonds and reversible reactions in Chemistry.
Another basic application of Thermodyanmics is in the equations of State and Phase Transitions. Where significant energy changes are involved and large entropy variations are observed.
This is, as I’ve highlighted before, the bare basics of what is otherwise a complex field. I’ll cover our next topic very soon.
Stay Tuned,
Ishaan