The Third Law of Thermodynamics says that a perfect crystalline structure at absolute zero temperatures will have zero disorder or entropy.
However, if there is even the smallest hint of imperfection in this crystalline structure, then there will also be a minimal amount of entropy. This law gets a little strange though, because even at zero Kelvin there is still some atomic movement happening, so it’s a bit theoretical. Regardless, this law allows us to understand that as the entropy of a system approaches a temperature of absolute zero, the entropy present within a system decreases.
The Third Law of Thermodynamics. (Image source)
ZEROTH LAW:
It says that if two systems are in thermal equilibrium with a third system, then the first two systems are also in thermal equilibrium with one another.
Using our good old Transitive Property of Equality: If System A is in balance with System C and System B is in balance with System C, then, System A and System B are also in balance with each other.
This law allows you to define the direction of heat flow between systems. If you know the temperature of a set of connected systems, then you’ll know which direction heat will travel based on the fundamentals of thermal equilibrium.
Note that while we’re covering the Zeroth Law last, it actually comes first. In the 18th century when the Laws of Thermodynamics were defined, only the first three were included. However, scientists realized that they needed a fourth law that defined the movement of temperature. Rather than renumber all of the existing laws and add confusion to existing literature, English scientist Robert Fowler came up with the name Zeroth Law.
Here's a sample computation:
TEST YOURSELF
Here's a sample computation:
Here's a more detailed lesson:
TEST YOURSELF
This is a great and clear explanation of the Third Law of Thermodynamics! You’ve broken down a rather abstract concept, entropy at absolute zero, into accessible language. I especially appreciate how you acknowledge the theoretical nuances (such as residual atomic movement). The inclusion of the Zeroth Law as context also helps readers situate the laws more holistically. One suggestion: perhaps you could add a simple real-world example or visual aid to make the ideas even more tangible.
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