In this house, we obey the laws of thermodynamics!
One scientific field sparks fear in all engineering students and may spark joy in the physicochemist. It is thermodynamics. That special field, that tries to describe how energy and heat shape the universe. To think about thermodynamics is no ordinary task. I encountered my curiosity for it through a certain episode of the Simpsons. This sparked two questions? How do we obey the laws of thermodynamics and how do we break them?
Lets ponder on that for a while. First we need to talk about the laws of thermodynamics. There are three laws - ok three and a half.
Zero Law: All macroscopic parts of a system have the same temperature in balance.
So this is scientific for: Different Temperatures will always approximate to one another. If I open my stove with over a 200 °C to my kitchen with about 20 °C, thermodynamically I join two systems with one another, so they will strive for balance. My stove will drop in temperature and my kitchen will rise in temperature until both have roughly the same temperature. Because the space of the stove is much smaller, the overall temperature will get closer to the 20 °C of the Kitchen, but this is a topic for another time.
First Law: In an isolated System (inner) Energy is constant.
Energy cannot be created from thin air. It is only transformed from one form into another. In Thermodynamics we differentiate three types of systems: open, closed and isolated. In an open system we can transfer mass, heat and work to the surroundings. In a closed system we cannot transfer mass anymore, only heat and work. In an isolated system we cannot transfer neither. If we are to heighten the energy in a closed system we must do so, by pulling Heat Q and Work W form the surroundings and transforming it into Energy U. Which leads us to a fundamental Equation of thermodynamics:
ΔU = W + Q
The change in inner Energy U of our system is dependent on Work W and Heat Q. Note this in your mind because the transformtation to energy will become more important for the next law. Let's try it with Max Planck's wording:
Second Law: Every process occurring in nature proceeds in the sense in which the sum of the entropies of all bodies taking part in the process is increased. In the limit, i.e. for reversible processes, the sum of the entropies remains unchanged.
Ok. So hold up. What in the name of Durin is ENTROPY? That is a question that even skilled Physicists and Physcochemists may not fully answer. In short: Entropy is a measurement for the chaos in the universe. It dictates the direction of outcome in a thermodynamic process. So in this sense Entropy S is effective when ever we transform Heat and/or Work in Energy and vice versa. For example in a power plant we use charcoal and burn it, thus generating huge amounts of heat which through steam and a turbine we transform into energy. But we cannot use our energy to get our charcoal back as it was. Thus this process is irreversible, which means we need to have produced entropy. An increase in entropy always speaks of irreversible processes. We cannot see if entropy is produced or is changed. We can only calculate it. And since I don't want to bore you with to much math, I will skip the equations and go on to the third an final law. So lets hear it from Einstein.
Third Law: The entropy of any substance approaches a finite value as the temperature approaches absolute zero.
I know what you are thinking. What the f*** is that supposed to mean? Well, the third law of thermodynamics describes mostly the impossibility of reaching absolute zero - the point, where there is no movement of particles whatsoever. Quantummechanics forbids this state and so does the sector of thermodynamics. We cannot determine the absolute entropy of a substance - we can only detect the change in entropy, so at absolute zero we should be able to define the entropy of a given substance - as we are not allowed to do so, absolute zero cannot exist.
Well now where we do know the fundamental laws of thermodynamics, how do we break them?
In the given episode I mentioned early Lisa Simpson has build a machine that constantly transforms work in energy and vice versa. Since it is not connected to an outside power supply, it should eventually run out of energy to do so, since we lose energy through friction and entropy. Since we move heat and work to create energy, we also produce entropy or by other means increase entropy. But it gets worse. It creates more energy since it runs faster and faster. So she creates energy out of thin air. Well by all means this breaks more than on law of thermodynamics. What Lisa Simpson created is per definition a perpetuum mobile - a machine, that never stops moving. There are different kinds of those perpetual motion machines. Lisa obviously build the first kind, which creates energy out of nothing thus violating the first law of thermodynamics. In reality no one has seen such a thing. Many people have tried, but none succeeded, mainly because thermodynamics don't break.
So lets recap this. There is a simple meme-esque summary of the laws of thermodynamics:
- You can't win
- You can't break even.
- You can't stop playing.
Since energy is constant in the system, you cannot win it. Since Entropy happens to increase and never decrease, you cannot break even. And lastly since there is no absolute zero where you could determine entropy, the game never stops.
I hope you have enjoyed this short trip to the world of thermodynamics. See you next time!
Keep spinning,
yours truly
Nils