By Anonymous
Entropy is a core concept in both physics and chemistry that describes the level of disorder or randomness within a system. The second law of thermodynamics states that entropy will either increase or stay constant in an isolated system over time.
What is Entropy?
Entropy refers to the amount of disorder or unpredictability within a system. A system with low entropy is highly ordered. However, over time, systems tend to move towards a state of higher entropy, where the components become more randomly arranged. This progression is not random, but rather, predictable, as shown in the second law of thermodynamics.
The reason entropy increases is that there are more ways for particles or components to exist in a disordered state than in an ordered one. Because disorder is statistically more likely, natural systems tend to evolve toward higher entropy.
Applications of Entropy
Your Bedroom
When you first tidy up, everything is neat and organised -clothes are folded, and your desk is in order. That’s low entropy, where everything is in its place. But, as time goes by, and you get a bit lazy, clothes start to pile up, books are scattered around, and before you even know it, your room is a disaster zone. Things naturally tend towards disorder (higher entropy)!
Gases
On a molecular level, the same principle holds true! When you open a can of Coke, CO2 gas that was dissolved in the liquid escapes to the surrounding area . Initially, the CO₂ gas is concentrated inside the can (low entropy), but as it spreads out into the environment, the system becomes more disordered, resulting in an increase in entropy.
Computer Science
Imagine you take a picture of a clear blue sky with very little detail. The image has low entropy because most of its pixels are similar (mainly blue). Data compression algorithms, like JPEG, can take advantage of this simplicity to reduce the file size by removing redundant information, making it easier to store.
On the other hand, if you take a photo of a crowded city street with many details, the image has high entropy because it's more complex and less predictable. Compression algorithms will struggle to reduce the file size significantly since much more information is needed to capture all the details.
The Big Bang
The Big Bang marked the beginning of the universe in a low-entropy state, where all matter and energy were concentrated in an incredibly hot, dense, and uniform singularity. As the universe expanded and cooled, entropy began to increase, with particles spreading out, forming atoms, stars, galaxies, and other structures that we see today, all of which contributed to greater disorder and complexity. Over time, the universe evolved from this highly ordered state to one of increasing entropy.
Chemical Reactions
In chemistry, entropy determines whether a reaction will occur spontaneously. We consider a reaction being spontaneous if there is an overall increase in entropy. For example, when petrol burns in an internal combustion engine, the chemical reaction transforms oxygen and fuel into CO2 and water.
2C8H18(l)+25O2(g)→16CO2(g)+18H2O(g)
The overall entropy increases because the number of gas molecules increases from 25 to 34 and the phase changes from liquid to gas!
Gibbs Free Energy and Spontaneous Reactions
Adding on to the 5th application above, another key concept in determining whether a chemical reaction will occur spontaneously is Gibbs free energy, G. This thermodynamic potential combines both enthalpy and entropy to provide a more complete picture of a system's energy state.
The formula for Gibbs free energy is:
G = H − TS
where: G is the Gibbs free energy, H is the enthalpy of the system, T is the temperature in Kelvin, S is the entropy of the system.
For a reaction to be spontaneous, the change in Gibbs free energy, ΔG, must be negative ( i.e. ΔG<0). This indicates that the reaction will proceed without needing an external input of energy, corresponding to a state of higher entropy.
Conclusion
Entropy is the universe’s method of turning order into chaos. Be it the spontaneous nature of chemical reactions, or the behaviour of gas molecules, entropy is something fundamental that shapes the world around us. Ironically, while entropy may cause mess and disarray, it is a key to explaining the origins of our universe. And the universe never takes a day off in making things messy!
Reference
Entropy and the teenager's bedroom
AN INTRODUCTION TO ENTROPY
Entropy and the 2nd & 3rd Laws of Thermodynamics
Ask Ethan: What Was The Entropy Of The Universe At The Big Bang?
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