The laws of thermodynamics are the laws that govern the relationship between heat and mechanical work, and they are very relevant to our daily lives. The second law of thermodynamics, the law of increasing entropy, explains that natural phenomena occur in a direction of increasing disorder. It emphasizes the importance of conserving energy and protecting the environment, and small actions in our lives can make a big difference.

The laws of thermodynamics: a big title, but not difficult!

The laws of thermodynamics are laws that govern thermal phenomena and the flow of energy based on the fundamental relationship between heat and mechanical work. There are four laws (the 0th, 1st, 2nd, and 3rd laws of thermodynamics). The name “laws of thermodynamics” may seem like a technical term for people who don’t study thermodynamics, and it may not be very relevant to their lives. However, the laws of thermodynamics are deeply relevant to everyone’s daily life, and they are not very technical. On the contrary, it’s fun and necessary to know.
If you look at the laws of thermodynamics in a thermodynamics book, it is difficult to understand because they are expressed in formulas that cannot be found in Korean. When the laws of thermodynamics are explained in words, you’ll think, “Oh, that wasn’t so difficult! For those who are intimidated by the laws of thermodynamics, let’s familiarize ourselves with them, especially the second law of thermodynamics, which is closely related to our daily lives!

The second law of thermodynamics: change in the world occurs in the direction of increasing disorder!

The second law of thermodynamics is also known as the law of increasing entropy. It states that “changes in natural phenomena occur in the direction of increasing the total amount of entropy, and not in the direction of decreasing the total amount of entropy.” In other words, it determines the direction of natural phenomena. When we refer to ΔS as the amount of entropy change, we can state that ‘ΔS is greater than or equal to zero’.
But what is ‘entropy’ in this context? Entropy is simply ‘disorder’. There is no strict definition of entropy, but it can be understood as the same as disorder in everyday use. For example, consider the solid state of ice: the water molecules in ice are fixed and cannot move from place to place. Therefore, the shape of the ice is also fixed, i.e., it has a low degree of disorder and is orderly. When the ice melts and becomes liquid water, the water molecules can move around fluidly, which means the disorder is higher than in ice. The same is true when water boils and becomes water vapor. Gases have more molecular motion and are more active than liquids, which is similar to the phenomenon of books on a bookshelf becoming a mess on a desk.
So, in layman’s terms, the second law of thermodynamics states that most chemical changes in nature occur in the direction of increasing disorder, not the other way around.

Increasing entropy is analogous to how a room gets messy when we use it!

Let’s take an analogy from our lives. Let’s say you put Chulsoo, a 20-year-old young man living in neighborhood A in Seoul, South Korea, in a room and seal the room so that no energy or matter can enter the room from the outside. (A room that is isolated from the outside world is called an “isolated system.”) Let’s observe Chulsoo in this isolated state for a day or so. What do you see? The room is in chaos. The books on the bookshelf, which were neatly organized before he entered the room, are all over the place, and there is a foul odor from his excrement. In other words, the level of disorder has increased.
However, one might argue. If Cheol-su is more organized, entropy decreases. But even so, disorder increases. The disorder increases because of the sweat and heat from his hard work, and the excrement and heat that would naturally be released even if he was just standing still and not making a mess. There is a “cost” to reducing entropy, and if the cost is taken into account, the overall entropy will eventually increase. It never changes in the direction of decreasing entropy. It is also impossible to reverse the increased disorder. This irreversibility is called an “irreversible process”.

The second law of thermodynamics determines the direction of natural phenomena!

There are many processes in nature that don’t actually happen. For example, if you put a cold substance in contact with a hot substance, heat will always move from the hot to the cold. The opposite will never happen. It’s an “irreversible process. If you drop ink into water, it will spread evenly throughout the water. This is also an increase in disorder and follows the second law of thermodynamics. It’s hard to imagine the ink spontaneously gathering back into one place. On a larger scale, if we consider the universe as an isolated system, the disorder of the universe as a whole is constantly increasing.
Let’s take a more topical example. Coal and oil, which are useful to us, are solids and liquids, which are more stable than gases, meaning they have low entropy. Now, when you put it in a car and burn it, it turns into gases, such as carbon dioxide, water, and sulfur dioxide. Gases have high entropy, so the chemical change has occurred in the direction of increasing entropy. But what about the reverse process? It’s impossible for the gases from burning oil to naturally collect and turn back into oil, which is an “irreversible process.” Therefore, the entropy of the Earth continues to increase.

Increasing entropy is not a good thing!

Our industrialized, petroleum-energy society is rapidly depleting the planet’s finite petroleum resources and is becoming an increasingly energy-hungry society, which means that the rate of entropy growth is accelerating. If entropy continues to increase at the current rate, fossil resources will soon be exhausted and environmental problems such as global warming and air pollution will intensify. Since it is impossible to reduce the increased entropy, we need to be alert to resource issues, environmental issues, and be careful in the use of resources. We cannot stop entropy from increasing, but we can slow it down by saving energy individually. Basic energy conservation practices, such as using less air conditioning and taking public transportation, can collectively make a big impact. Why don’t we all try to remember the second law of thermodynamics in our daily lives?

What the laws of thermodynamics can teach us

Understanding the laws of thermodynamics not only helps us in our daily lives, but also in understanding how the Earth and the universe work. It can help us be more efficient with the energy we use and reduce unnecessary energy waste. The laws of thermodynamics are also important concepts that underlie technological progress and innovation, and will play a key role in solving future energy challenges.
We need to be more conscious of the laws of thermodynamics in our daily lives. Think about how all of our resources are being used – the electricity and gas in our homes, the food and water we consume – and how energy is being transformed in the process. These small actions can add up to make a big difference.
The laws of thermodynamics are not just scientific knowledge, they are important laws that are intimately connected to our lives. Understanding and practicing them is the first step to a better future.