Entropy (Simplified)

entropy which is represented by the symbol. S is the measure of disorder which is connected to randomness of molecules or chaos in general, in the universe. Um It's related to systems surroundings and the universe. Now we're going to stay connected to entropy is the second law of thermodynamics. It states that the entropy of the universe is always increasing, so chaos and disorder is always increasing. The universe stars, dies, planets break apart. It's just a normal progression of the universe. Nothing lasts forever. We're gonna say, connected to this also is the idea of spontaneity. So the second law says that the universe is entropy is always increasing. Well, all spontaneous reactions involve an increase in entropy of the universe, right? So basically this is connecting to spontaneity.

So here the second law of thermodynamics leads us to conclude A The total energy of the universe is constant. We'll know Where did it talk about? The energy of the universe is talking about the randomness or chaos of the universe. The disorder of the universe is increasing with the passage of time. That is true. It says entropy is increasing, so over time it's going to get more and more chaotic. Universe is don't last forever, planets and stars die. This is the natural progression of the universe. The total energy, the universe is increasing with time. Again, we don't know anything about energy. That's not what the second law is related to. So both C and D. Are out. So here the answer would have to be option B.

So we can say we can determine the sign of the entropy change which is delta. S. In a system by examining physical and chemical changes. Now we're going to say that our entropy change which is delta. S. Is a measure of increase or decrease in order due to chemical or physical changes. So here let's take a look at entropy and physical changes. First, we're going to say in this first image, we're transitioning from our solid to liquid to gas. We're heading in a direction where the space between the molecules is increasing and if you think about it, which is more chaotic, a solid object is sitting there on the table or a container filled with gasses that are bouncing everywhere. We'd say that gasses have the most entropy. So as we're heading from solid towards the gasses we're going to say that our entropy is increasing. That means that our delta S value is going to be positive. There's a positive change in entropy. We're going to say that this move from solid to gas is usually accompanied by an increase in our temperature. Think about it, increasing temperature on a solid would cause it to melt, increasing it further, would cause that liquid to become vaporized into gas is Now let's think about the opposite direction. If we were to decrease the temperature molecules would come closer and closer together are gasses would condense down into liquid and if we lower the temperature even more, they would freeze into a solid as we head from gas to solid, we expect a decrease in entropy. So a negative change in entropy. Alright, so now that's physical changes. Let's look at chemical changes here, we can say that we can have entropy increasing, So positive delta. S. If we are breaking bonds right? Remember chaos chaotic disorder. The more things we can break apart, the more chaotic things become, so breaking bonds is a chaotic action. We can also say if we look at this chemical reaction, we have calcium carbonate solid, it breaks apart into calcium oxide and carbon dioxide gas. It's an increase in chaos because we are breaking bonds, but it's also an increase in chaos because we just increase the moles of gas. So there's an increase in moles of gas. Remember gasses have the most entropy, their molecules are further spread apart, bouncing everywhere now, entropy decreasing. So a negative change in delta S is if we did the opposite if we're forming bonds or if we decreased the number of moles of gas here, we have one mole of nitrogen gas plus three moles of hydrogen gas. For a total of four moles of gas They combined together to give me two moles of gas here. So not only am I forming bonds, but I decreased the number of moles that I have. You don't have to have both happen, but as long as one of these is happening, That tells us if there's an increase or decrease in entropy if you're breaking bonds, it's an increase in entropy. If you're decreasing the number of moles of gas, it's a decrease in entropy. Both don't need to happen for this to be an increase, right? So keep in mind the different physical and chemical changes and how they can infect the increasing or decreasing of entropy.

which one of the following processes produces a decrease in the entropy of the system boiling water to form steam. He remember boiling means we're breaking bonds as we transition from a liquid to a gas. Breaking bonds causes an increase in entropy melting ice to form water. Here, the same situation happens, we're breaking bonds in this case we're going from solid to liquid. So that's going to be an increase in entropy mixing of two gases into one container. We had one container with gases now even increased by it even more, more gas is more fun, more chaos. So this is going to increase entropy as well, freezing water to form ice. So we're going from liquid to solid. So we're forming bonds which is a decrease in entropy. So this will be our answer. Now let's look at you just to make sure that he is not an answer as well. The dissolution of solid potassium chloride and water so dissolution or dissolving and we're breaking it down so it's going from k C. L. Into its ions. So you're breaking the connection so that's breaking bonds, so that's an increase in entropy. So here only option D would be a decrease in entropy of the system.