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Second Law of Thermodynamics and entropy

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Second Law of Thermodynamics and entropy: the entropy of the universe constantly increases.

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  • aqualine ultimate style avatar for user c2j
    If we could understand all of the bare fundamentals of how all molecules behave and interact, and we could also take a "snapshot" of every molecule and it's state in the universe,

    Then from that, would we be able to technically predict everything that will ever happen, inside of our universe?
    (12 votes)
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  • blobby green style avatar for user Julia Kocherzat
    If entropy only increases in the universe, and that is meaning that there is more and more heat, how does that relate to the notion that energy can be neither created nor destroyed? This definition of entropy is making it seem like energy is being created and that there is more and more of it.
    (4 votes)
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  • piceratops ultimate style avatar for user Yash
    (6 votes)
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  • winston baby style avatar for user AJ
    If we cannot create/destroy energy, shouldn't the number of states remain the same?
    (4 votes)
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  • blobby green style avatar for user Sanita Seile
    Energy cannot be destroyed or created.. How can entropy in the universe increase if it still contains the same amount of matter/ energy.
    Or does the Universe creates new energy/ matter? :)
    (3 votes)
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  • primosaur ultimate style avatar for user nickeldime88
    How can entropy increase if a star explodes and it forms an ordered panorama of stars? How can entropy be irreversible if cooler particles collide with the cooler particles?
    (3 votes)
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    • blobby green style avatar for user mustafasethi786
      For your first question, entropy would increase if a star explodes because all of the tiny particles and molecules would move out (explode) which would mean that there is more variation of the molecules. For example some molecules would be on the right and some would be on the left. As the star explodes the molecules would be all over the place and would increase the entropy.
      For the second question, Entropy could be reversible but its like a one out of millions of millions of millions. because there is such a low probability it is almost impossible.
      (1 vote)
  • aqualine ultimate style avatar for user sassafraswest
    Doesn't this disprove evolution? if something is left to itself, wouldn't it just get worse, instead of getting more complicated, as evolution says?
    (1 vote)
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    • male robot hal style avatar for user Charles LaCour
      Nope. There is source of low entropy energy that comes from the sun. The process of life and evolution is converts this low entropy energy into higher entropy waste energy.

      If you look into the way complex systems that are not in equilibrium change over time their complexity will increase to a point and then degrade into low complexity as the lower entropy system transitions into a higher entropy system at equilibrium.

      If you look at a starting system where you have a layer of cold cream on top of a layer of hot coffee which has low entropy and low complexity. Over time these two fluids will start to merge and mix as they transition to equilibrium. As they mix there will be complex patterns of streaks of cream and coffee but when it comes to equilibrium you have a homogenous mixture of cream and coffee with low complexity.
      (4 votes)
  • leaf grey style avatar for user Anshari Hasanbasri
    I take the example about the container. I kinda understand why the first container has smaller entropy, and the second has larger. But what if the system has reached maximum entropy - that the molecules have diffused as vast as they could/possible in the container? The entropy increase must be stopped right? This statement still sounds counterintuitive to me. Can anyone explain it a bit clearer, or did I miss something?
    (1 vote)
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    • winston baby style avatar for user Ivana - Science trainee
      Why do you think it is counterintuitive? You are right, once molecules reached maximum entropy since molecules diffused as vast as they could it is the end.

      So you ask why entropy is constantly increasing int he Universe?

      Well, our observable Universe is not one container which can take up a fixed volume of molecules. The universe is constantly expanding.
      (4 votes)
  • aqualine ultimate style avatar for user Aryan Chaubey
    Does it mean that the universe is gaining more heat?
    (1 vote)
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  • primosaur seedling style avatar for user M. B. McConnell
    I know that the Second Law of Thermodynamics explicitly states that the amount of entropy in the universe is always increasing. However, how does this law hold up when determining a reaction spontaneous? I know that if a reaction is spontaneous, entropy is increasing in that instance, thus abiding by the law. But, I also know that some reactions, like the process of ice melting into water, are not spontaneous and therefore, entropy decreases, which directly contradicts the law. Are these separate principles, or am I missing a factor in determining a reaction spontaneous?
    (1 vote)
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    • male robot hal style avatar for user Andrew M
      Entropy increases when the ice cube melts, it doesn't decrease.
      Anyway, the law says the entropy OF A CLOSED SYSTEM increases. Can we make ice, even though it decreases entropy? Of course we can. We just bring in energy from outside the system.
      (3 votes)

Video transcript

- [Voiceover] The Second Law of Thermodynamics, one statement of it is that the entropy of the universe only increases. And, I put an exclamation mark here, because it seems like a very profound statement. And, on a lot of levels, it is. And, just to get us into the right frame of mind, I have this image here from the Hubble telescope of the night sky. And, each of these dots, these are not stars. These are galaxies. That's a galaxy. That's a galaxy there. That's a galaxy. So, hopefully this gets you into little bit more of a cosmological scale. But, let's think about what this is actually telling us. The entropy of the universe only increases. So, entropy, we can define that as the disorder of a system. And, we're really talking about the number of states that a system could take on. And then, we're saying the universe. But, we could also say the entropy of a closed system only increases. A system that is fully contained, that's not interacting with its surroundings, because the universe is the ultimate closed system. There's nothing for it to, outside of it to interact with thermodynamically. And, I'll do a quick review of open and closed systems, just so we make sure we understand that. So, if I had a campfire, so I have some logs and I had my, the flame going right over here. So, that's the campfire. If I were to just look at the logs and the fire, that's going to be an open system. Because, it's clearly interacting thermodynamically with its surroundings. It's releasing heat. It's warming up the air molecules around it. It's releasing light out into the universe. There could be interactions from the rest of the universe into the system. So, it isn't isolated from the rest of everything else. But, a closed system, it is isolated. And, there are, it's very hard to create a true closed system in our everyday life. But, we can approximate it. And, the one that you've probably experienced in the not too distant past is an ice cooler. And, an ice cooler, we're at least attempting to thermodynamically isolate, isolate the inside of the cooler from the outside, from the rest of the universe. So, this is, and the way we do it is we have some type of an insulating material. Maybe some styrofoam. And, we could put, you know, we'd use it to maybe store ice. But, it's not a perfect closed system, because eventually, the heat from the rest of the universe will warm up the walls of the cooler. And eventually, that heat will warm up, will be transferred to the ice, and it will warm it up. And, it will melt it. So, it's not a perfect closed system, but it's a good approximation, because we're at least attempting to isolate it thermodynamically from the rest of the universe. And, I can even make a little cover of this to show that we really wanted to isolate it. And, in research labs, you'll see things that are much better approximations of closed systems. But, even those at some level are, they're going to interact with the rest of the universe. The ultimate closed system, so this is a closed system, is really the universe. Nothing to interact with outside of it thermodynamically. So, let's think a little bit about this definition. The entropy of the universe only increases. Why does this make intuitive sets? Well, the best example I can think of is just straight up diffusion. So, if I were to have, let's say I have a container. So, I have a container, and I'll make it a, I'm gonna make it a closed container. We'll say this is some type of theoretical ideal closed system here. Now, let's say I had some ideal gas. So, I had some ideal gas molecules right over here. They have some average temperature, but that means they all each have their own individual, their own individual kinetic energy. They're all bouncing around in different ways. What's going to happen over time? Well, over time, the ones on the left here, they're gonna bounce off this wall. And then, they're eventually gonna go in this direction. And so, over time, you're gonna have a situation where the system is going to look something more like this. So, the system is going to look more like this, where instance, let's see, this is six particles. These six particles are gonna diffuse throughout the container. So, they're gonna diffuse throughout the container. They're going to take up more of the space of the container. Now, what just happened in that process? Well, when you knew that the particles were confined to this little section of the container, there were fewer possible states. You had lower entropy than when you are here, when you know that it's filled up the container. There's more possible locations, more possible orientations for it. And so, you are going to have more states. You have higher entropy, higher, higher, higher, entropy. And, in general, these processes where you have the entropy increasing, we call these irreversible processes, irreversible, irreversible processes. And, why is it irreversible? Well, there's some probability that these molecules might just gather back into this corner of it. But, it's very, very low probability. And, this is when we're dealing with six molecules. But, in real systems, we'd be dealing with much larger than six molecules. We'll be dealing with millions of millions of millions of millions of molecules. So, things with, between 20 and 30 zero's of molecules. And there, it's very unlikely that they just all bump together in the right way to start taking a smaller volume, when they could actually fill the container. And so, that's why you don't see, that's why you don't see smoke just naturally turn into to some type of shaped particle, or take up less space, as opposed to filling its container. So, this is irreversible, because you went from, you went from fewer number of potential states, as a smaller volume, to a higher number of potential states. And, the universe is constantly doing this. That's why the entropy of the universe is only increasing. Now, there's some processes that it feels like the entropy isn't increasing that much. So, if you were to take one billiard ball right over here, and you were to roll it, you were to roll it into another billiard ball right over here, and transfer the momentum to that one, it feels like that could go the other way around. Like, that other billiard ball could hit this one and go backwards. And, at a macro level, it feels like this is a reversible process, and people will tend to call this reversible. But, if you really were to go on a microscopic level, and it looks like the entropy isn't increasing that much, but if you were to look at it on a microscopic level, and just to be clear, the entropy, you know, when this ball is moving and this is stationery, going to a state where this is moving and this is stationery, it doesn't look like the entropy is increasing that much. And so, that's why they tend to call this irreversible, because you tend to observe things where maybe this one, it could go backwards. This could hit this one and then, this one could go, you can kind of run the film in rewind. But, even there, if you were to look at a microscopic level, you would see that some heat is being generated, and that some molecules in the ball are getting excited as they collide, and as they have friction with the air, and as they, roll on the ground over here. And, you're never going to get those molecules to go back into the state that they were before, that you actually do have the entropy increasing in the system. So, even when in our every day lives, in thermodynamics, people talk about reversible processes. They're only approximately reversible, and that the entropy's only increasing a little bit. It's not like there's zero increase in entropy. Irreversible reactions, these are the ones. Diffusion is a very obvious one, where it's very clear that you have an increase in entropy, and it feels like it's a very, very low probability, or almost zero probability of this thing ever going back to where it was. And, you won't observe it, because we were talking about that many molecules. Something with 20 or 30 zero's of molecules. The odds of all of them just doing the right thing, you could wait around a very long time and never actually observe that happening. And so, hopefully this makes sense that the disorder in this way, the number of states only increases as you have more and more interactions. And, a lot of that is coming from heat. Everything you're doing right now, when I'm making this video, my body is generating heat. That heat is dissipating into the universe. That is adding to the number of states that the universe can actually take on. As I move my hands up, my little digital pencil that I'm using is causing friction. That's releasing heat into the universe. My computer is running and releasing heat into the universe. You watching this, releasing heat into the universe. The electrons traveling on the wire to your computer, releasing heat into the universe. And, all of that is increasing the number of states. So, if you're thinking on a molecular level of everything.