What Is The Meaning of Entropy?
Entropy is a term regularly used in the physics and engineering world. Engineers are aware of the term due to the definitions of the second law and the third law of thermodynamics. However, engineers will give you a different meaning of entropy depending on the individual.
The Thermodynamic concept was first observed by William Rankine, who also developed the Rankine Cycle. It was discovered back in 1850 however the terms thermodynamic function and heat-potential were used instead of entropy.
Second Law of Thermodynamics
The second law of thermodynamics is defined as “the total entropy of an isolated system will not decrease over time and will remain constant only if all processes are reversible.”
dS = delta Q / T
dS = Change in Entropy, Delta Q = Heat transferred to the system, T = Temperature
Entropy Definition and Meaning
The definition and meaning of entropy is stated as “a thermodynamic quantity representing the unavailability of a system’s thermal energy for conversion into mechanical work often interpreted as the degree of disorder or randomness in the system”.
Isentropic Process
Many systems and processes within Thermodynamics are classified as isentropic, but what does it mean? An Isentropic process is a process that occurs at constant entropy. Throughout the entire process, the entropy of the system does not change. Relating an isentropic process back to the definition stated above, the process is also considered adiabatic and reversible.
It is common for the process to be called isoentropic, but unfortunately, this is not the correct spelling/pronunciation.
Examples of Entropy
Campfire
A great example of entropy is a campfire. The campfire starts as solid pieces of wood. Next, you light the wood, and it begins to burn, burning down into ash and generating a fire. Each state of the fire shows an increase in entropy.
The ‘randomness’ at each stage of the process increases. A solid wood log has zero ‘randomness’, whereas the ash and fire have high randomness or disorder.
Ice melting
Ice melting is another great example. An ice block has low entropy due to a low level of disorder and randomness. However, as the ice melts and becomes water, the randomness and disorder of the system increase.
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