The total entropy of the universe is never decreasing, rather, the total entropy of the universe is either increasing or remaning constant depending on the thermodynamic process that is applied, reversible or irreversible. The change in entropy of a thermodynamic process is equal to the heat transfer of a system divided by temperature.
For reversible thermodynamic processes, the total change in entropy of the system and the surroundings remains constant such that ΔStotal = 0.
For irreversible thermodynamic processes, the total change in entropy of the system must always increases towards more “disorder” such that ΔStotal > 0.
Second Law of Thermodynamics
1. The second law of thermodynamics states that not all heat can be converted to work such that some of it will always be lost to the surroundings (Kelvin statement).
2. The second law also states that heat cannot be transferred from a cold reservoir to hot reservoir without the addition of extra work (Clausis statement).
The thermodynamics principle involved in the process of refrigeration is the “reverse” process of a heat engine, where extra work is needed for heat to flow from a cold reservoir to a warm reservoir.
The process of refrigeration directly follows the Clausis statement of the second law of thermodynamics where heat is taken in from a cold reservoir, work is applied, and heat is expelled to a hot reservoir- a cyclic heat engine process known as the “reverse Carnot Cycle.”
A refrigerator’s net effect is to remove heat from a cold reservoir, making the reservoir colder, and transferring the removed heat to a hot reservoir, making the hot reservoir even “hotter.” This process in consistent with the discussion of entropy, such that the total entropy of the universe is never decreasing.
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3. Hall, Nancy. “Second Law of Thermodynamics.” Second Law of Thermodynamics. NASA, 5 May 2015. Web. 2 Dec. 2015. <https://www.grc.nasa.gov/www/k-12/airplane/thermo2.html>.
4. “But Wait!” Dave’s Physics Shack. Morningside College. Web. 2 Dec. 2015. <http://webs.morningside.edu/slaven/Physics/entropy/entropy6.html>.