Gibbs free energy and spontaneity (video) | Khan Academy
Quick tips The change in enthalpy and change in entropy of a reaction are the driving Combustion reactions, such as this fire, are spontaneous reactions. . What is the relationship of the free energy change, ΔG, to the. Quick tips Entropy is a measure of the degree of randomness or disorder of a system. . spontaneity of a reaction are the enthalpy and entropy changes that . Relationships between enthalpy, entropy, and free energy are. basic thermodynamic concepts, including spontaneity, entropy, and enthalpy Lab Tips. This lab is designed for students to work together, discussing and . This famous relationship of free energy change to changes in enthalpy and.
For a system with constant entropy, volume, and number of particles, NSV the internal energy or total energy is the thermodynamic potential. For a system at constant entropy and pressure NSPenthalpy is the thermodynamic potential.
Gibbs free energy and spontaneity
And for a system at constant volume and internal energy NVEthe negative of entropy is the thermodynamic potential. In other words, all of these thermodynamic variables are interconnected, and a change in one affects all of the others. You can hold three constant at any given time and still allow the system to "move" through phase-space. Which thermodynamic potential you need to describe how the system will move depends on which variables you choose. This makes sense, since we know that exothermic processes tend to be spontaneous, because they are releasing energy and therefore the final system energy is lower than the initial.
This also matches up with what you know - an increase in entropy indicates a spontaneous process. For your last question: I am really having a hard time in figuring out a reaction where energy decreases and entropy increases. Let's look at the other possibilities: And say he's got one guy like that there, and then I have another guy like this, and let's say he's got a molecule like this.
Let's say that a more-- well, I won't say stable or not. But let's say that when these guys bump into each other, you end up with this. And I'm making things up on the fly. Maybe one of these molecules bonds with this molecule, so you have one of the dark blues.
I'll draw all the dark blues. Bonds with this light blue molecule, one of the dark blues bonds with the magenta molecule. And maybe that brown molecule just gets knocked off all by himself. So we went from having two molecules to having three molecules.
We have more disorder, more entropy. This can obviously take on more states. And I'm telling you that delta H is less than 0. So by doing this, these guys, their electrons are in a lower potential, or they're in a more stable configuration.
So when the electrons go from their higher potential configurations over here, and they become more stable, they release energy.enthalpy, entropy and Gibbs free energy
So you have plus-- and then I just know that, because I said from the beginning that my change in enthalpy is less than 0. So plus some energy. So it seems pretty obvious to me that this reaction is going to be spontaneous in this rightward direction. Because there's no reason why-- first of all, it's much easier for two particles to bump into each other just right to go in that direction than it is for three particles-- if you just think of it from a probability point of view-- for three particles to get together just right and go in that direction.
And even more, these guys are more stable. Their electrons are in a lower potential state. So there's no even kind of enthalpic reason for them to move in this direction, or you know, kind of a energy reason for them to move in this direction. So this, to me, I kind of have the intuition that regardless of what the temperature is, we're going to favor this forward reaction. So I would say that this is probably spontaneous. Now, what happens-- let's do something that's maybe a little less intuitive.
What happens if my delta H is less than 0? But let's say I lose entropy. And this seems, you know, with second law of thermodynamics, if the entropy of the universe goes up.
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I'm just talking about my system. So that would be a situation where I go from, let's say, two particles. Let's say I got that particle, and then I have this particle. And then, if they bump into each other just right, their electrons are going to be more stable, and maybe they form this character. And when they do that, the electrons can enter into lower potential states, and when they do, the electrons release energy, so you have some plus energy here.
And we know that, because this was the change in enthalpy was less than zero. We have lower energy in this state than that one, and the difference is released right here. Now will this reaction happen? Well, it seems like-- let's introduce our temperature. What's going to happen at low temperatures? At low temperatures, these guys have a very low average kinetic energy. They're just drifting around very slowly.
And as they drift around very slowly-- And remember, when I talk about spontaneity-- I wrote sponteous. Sponteous should be another thermodynamic. It's a fun word. When I talk about spontaneity, I'm just talking about whether the reaction is just going to happen on its own.
I'm not talking about how fast, or the rate of the reaction. That's a key thing to know. You know, is this going to happen. I don't care if it takes, you know, a million years for the thing to happen.
I just want to know, is it going to happen on its own? So if the temperature is slow, these guys might be really creeping along, barely bumping into each other. But they will eventually bump into each other. And when they do, they're just drifting past each other. And when they drift past each other, they will configure themselves in a way-- things want to go to a lower potential state. I'm just trying to give you kind of a hand-wavey, rough intuition of things.
But because this will release energy, and it will go to a lower potential state, the electrons kind of configure themselves when they get near each other, and enter into this state. And they release energy. And once the energy is gone, and maybe it's in the form of heat or whatever it is, it's hard to kind of get it back and go on in other direction.
So it seems like this would be spontaneous if the temperature is low. So let me write that. Spontaneous if the temperate is low.
Now what happens if the temperature is high? Remember, these aren't the only particles here. You know, I'll have another guy like that, and another guy like that. And then this, on this side, I'll have, you know, more particles.
There's obviously not just one particle. Then all of these macro variables really make no sense, if we're just talking about particular molecules. We're talking about entire systems. But what happens here if the temperature of our system is high? The universe consists of the system and the surroundings together. Fill in the blanks below. Label the regions with the terms system, surroundings, and universe.
Gathering Evidence Place 5. Write the formula for ammonium nitrate and identify its solid type. Defining Entropy and Looking at Entropy Changes in a System Entropy is a mathematically defined property in thermodynamics. It can often help to understand it as a measure of the possible arrangements of the atoms, ions, or molecules in a substance. Pour mL of water over the salt in the beaker and stir. Can you still see the ammonium nitrate?
Make and record your observations: Using the terms cation, anion, solute, solvent, and solution, label the diagram below. Given the physical state of ammonium nitrate before it dissolves, how do the possible arrangements of the ions in the salt compare to their possible arrangements when free to move within the solution?
Does your answer to the preceding item suggest that the entropy of the ammonium nitrate increased or decreased upon dissolving? But more is going on than just ions leaving the solid and moving about more freely. Note in the figure above that the polar water molecules are attracted to and oriented around the dissolved ions. The ions are solvated.
- The Relationship Between Enthalpy (H), Free Energy (G) and Entropy (S)
This orientation of a lot of the water molecules reduces their freedom to move about in the liquid, so the number of possible arrangements of the water molecules is reduced when the ions are present.
For most salts with single charges on their cations and anions, like NaCl, KBr, or LiNO3, the positive change in entropy for the ionic solid separating into its ions in solution will predominate. Did dissolution of ammonium nitrate happen spontaneously?
Looking at Entropy Changes in the Surroundings by Defining Enthalpy We will now consider entropy changes in the surroundings by looking at another thermodynamic term, enthalpy. The enthalpy of a system has a definition in thermodynamics that relates to its internal energy, the pressure on the system, and the volume of the system.
It is useful in understanding the second law, however, because at constant pressure and volume, a change in enthalpy is the same as the thermal energy transferred from the system to the surroundings, or from the surroundings to the system. Case one for enthalpy Measure out mL of water in a clean mL beaker.