Who discovered the second law of thermodynamics? (And when?)

The short answer: German physicist Rudolf Clausius discovered the second law of thermodynamics during the year 1850.

Explanation: 

• During the year 1850, Rudolf Clausius discovered the second law of thermodynamics as; 
  
  “Heat can not itself flow from colder body to a hotter body.”
  
  This is known as Clausius statement in thermodynamics.

• Also in 19th century only, the another statement of second law was proposed by Lord Kelvin and Planck.
  
  This statement is known as Kelvin-Plank’s statement which is mentioned below;
  
  “It is impossible to construct a device (operating in a cycle) which works on a single heat source and converts all of its heat completely in to work”

• Later in 1865, Rudolf Clausius discovered the entropy statement of the second law of thermodynamics as;
  
  “The entropy of the universe tends to a maximum”

I hope you have got the answer to your question.

For more detailed information on Second law of thermodynamics, check the ultimate guide on Second law of thermodynamics.

(This guide has all the important knowledge about Second law of thermodynamics along with real life examples and lots more. You will love this guide for sure.)

Also see: 

Suggested important topics:

• What is Thermodynamics? (35+ topics with Definitions and basics)
• What is First law of thermodynamics?
  • First law of thermodynamics definition/statement (In simple way)
  • Examples of First Law of Thermodynamics / Law of conservation of Energy
  • First law of thermodynamics equation (A practical explanation)
  • Limitations of First Law of Thermodynamics
• What is second law of thermodynamics? [8+ Best examples to remember the law]
  • Examples of Second Law of Thermodynamics (8+ best examples)
  • Second Law of Thermodynamics Definition/Statement (Next level explanation)
  • Second Law of Thermodynamics Equation [Practical explanation]
• What is Third law of thermodynamics? (in simple terms)
• Laws of thermodynamics
• What is Carnot Cycle in Thermodynamics?
• What is the definition of entropy in thermodynamics?
• Heat capacity vs specific heat in thermodynamics
• What is Thermodynamic Equilibrium? (With Best Example)
• Thermodynamic Process (With Examples)
• What is Thermodynamic System? – Open, Closed & Isolated system (With Examples)