In this video, I want to talk about the second law of thermodynamics as it relates to heat energy and entropy. So let's say if we have a metal rod placed between a hot object and a cold object. Heat will naturally flow from hot to cold. to cold that's a simple natural process it's spontaneous it occurs on its own heat doesn't naturally flow from cold to hot it just doesn't happen the only way for you to make it happen is if you were to pump energy into the system So, for example, a refrigerator will take out heat energy from inside the fridge and pump it outside of it. And that's how a refrigerator can cool this stuff on the inside.
But it takes energy to do that. It doesn't happen naturally. A good way to illustrate this is, imagine if...
Let's say if you have a ball on top of the hill. The ball will naturally flow in a downward direction, the same way as heat flows from hot to cold. Heat flows from a high temperature naturally to a low temperature.
And this ball is going to flow from a high position to a low position. Now, if you place the ball at a low position, it won't naturally go towards a higher position. It just doesn't happen. The only way for you to make it happen is you've got to put energy into it to get it over that hill.
And the same is true for heat. Heat doesn't flow naturally from cold to hot. Now, you could make it happen. You can pump heat to warm up a certain environment.
Heat pumps do that. However, it costs energy to do so. Now, as heat flows from hot to cold, this is a spontaneous process. And for a spontaneous process, the entropy increases.
It's going to be greater than zero. And that's another statement of the second law of thermodynamics. For natural processes, the change in entropy will be greater than zero.
Now, if you have an ideal reversible process, at best, the entropy can be equal to zero. However, most systems do not behave perfectly, so a natural spontaneous process will tend to lead to higher disorder. So for natural processes, the change in entropy is positive.
It's greater than zero. And so that's the basic idea behind the second law of thermodynamics as it relates to entropy. Natural systems tend to go towards disorder. So, for example, let's say if you take your room.
It takes energy and effort to clean your room. Naturally, your room will tend to get messy and dirty and things like that. But it takes effort to clean it, even if you were to leave it alone.
Things will get old, houses worn down. Let's say if you leave your car out in the open for 10 years. It's not going to become newer, it just gets worse.
And so natural systems, they tend to go towards a state of disorder. rather than a state of order. For example, let's say if you drop a glass cup, it's going to break into pieces.
Now those broken pieces are not going to naturally just fix themselves together, it doesn't happen. So it's very difficult to take something in a disorderly state and turn it into an orderly state. It takes energy to do that. Naturally, things tend to go towards a disorderly state.
And so for natural spontaneous process, the entropy of the system tends to increase. And that's the general idea behind the second law of thermodynamics.