Note that when the entropy of a reaction increases, the reaction become more spontaneous. But a more technical and useful way to think about entropy is like this: entropy is a measure of the number of ways a system can be arranged. Most of the time though, the number of microstates is way too many to count, especially when we think about how many molecules we have to take into consideration in an average system.
When a group of molecules can move around freely, or if it can take up more space, its entropy will increase, because its number of arrangements increases. Think of it this way: ice is a fairly rigid block of water. The most they can do is vibrate in place, according to their absolute temperature.
Molecules of liquid water, however, can slip past one another at will, and can therefore spread out into puddles. The number of arrangements for the molecules increases when ice transforms to water, and therefore entropy increases. Similarly, when water vaporizes, the molecules spread out even further, and can be arranged anywhere throughout the entire room. Entropy dramatically increases. Now, of course, we can to consider a new question: if liquid and gaseous water are so high in entropy, and high entropy increases the spontaneity of a reaction, why does any ice exist?
Learning Objective Describe the differences between spontaneous and nonspontaneous processes. Key Points A spontaneous process is capable of proceeding in a given direction without needing to be driven by an outside source of energy. The laws of thermodynamics govern the direction of a spontaneous process, ensuring that if a sufficiently large number of individual interactions are involved, then the direction will always be in the direction of increased entropy.
An endergonic reaction also called a nonspontaneous reaction is a chemical reaction in which the standard change in free energy is positive and energy is absorbed. Endergonic processes can be pushed or pulled by coupling them to highly exergonic reactions. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet.
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And so, you can imagine if 'T' is high, if 'T' is high, this term's going to matter a lot. And, so the fact that entropy is negative is gonna make this whole thing positive. And, this is gonna be more positive than this is going to be negative. So, this is a situation where our Delta G is greater than zero. So, once again, not spontaneous. And, everything I'm doing is just to get an intuition for why this formula for Gibbs Free Energy makes sense.
And, remember, this is true under constant pressure and temperature. But, those are reasonable assumptions if we're dealing with, you know, things in a test tube, or if we're dealing with a lot of biological systems. Now, let's go over here. So, our enthalpy, our change in enthalpy is positive.
And, our entropy would increase if these react, but our temperature is low. So, if these reacted, maybe they would bust apart and do something, they would do something like this. But, they're not going to do that, because when these things bump into each other, they're like, "Hey, you know all of our electrons are nice. Hey, no reason to react here. And, if you look at these different variables, if this is positive, even if this is positive, if 'T' is low, this isn't going to be able to overwhelm that.
And so, you have a Delta G that is greater than zero, not spontaneous. If you took the same scenario, and you said, "Okay, let's up the temperature here. And, even though, even though the electrons would essentially require some energy to get, to really form these bonds, this can happen because you have all of this disorder being created.
You have these more states. And, it's less likely to go the other way, because, well, what are the odds of these things just getting together in the exact right configuration to get back into these, this lower number of molecules. And, once again, you look at these variables here. Even if Delta H is greater than zero, even if this is positive, if Delta S is greater than zero and 'T' is high, this thing is going to become, especially with the negative sign here, this is going to overwhelm the enthalpy, and the change in enthalpy, and make the whole expression negative.
So, over here, Delta G is going to be less than zero. Hopefully, this gives you some intuition for the formula for Gibbs Free Energy. And, once again, you have to caveat it.
It's under, it assumes constant pressure and temperature. But, it is useful for thinking about whether a reaction is spontaneous. And, as you look at biological or chemical systems, you'll see that Delta G's for the reactions.
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