In this video, we're gonna take a look at entropy which uses the variable s. Now it is the measure of disorder. This order could also be called randomness or chaos that exists within a system surroundings and universe. When we say system, we're just talking about a chemical reaction or an object of focus the surroundings is everything else together. They form our universe. Now, energy is dispersed between or because our system is not able to convert all energy into usable energy. With this idea, we have thermodynamics, thermodynamics describes the relationship between heat energy and reaction favorability. Now, recall the first law of thermodynamics energy cannot be created or destroyed nor destroyed, but it is transformed. So how does this relate to everyday life? Well, you might be seeing talks of energy transitions about EVs solar power and all this stuff. So let's take a look at this image. Let's imagine that this represents a battery and that battery is solar powered. So we have the sun here that's beaming its energy and the battery is absorbing it. This is transforming the energy it's converting it from solar energy to electrical energy. So now our battery is more charged up. But here's the thing, things like this are not 100% efficient. Some of the energy will not be absorbed by the battery and it's going to be lost. So this energy is lost as entropy as randomness. And this is a natural process, energy is not created nor destroyed, but not 100% of it is transformed or transferred cleanly. Some of it is lost as entropy. Now here, the second law of thermodynamics deals directly with entropy. It states that the entropy of the universe is always increasing. Remember entropy is chaos or disorder. We say that the entropy of the universe is always increasing. This kind of calls back to the whole Big Bang theory. The en the universe is ever expanding from a center. So the en the universe is moving outwards more disorder, more chaos planets die suns supernovas. All this stuff is a natural process of the universe. Now, here we're gonna say all spontaneous reactions involve an increase in the entropy of the universe. So we know that a spontaneous reaction will always cause our variable entropy to go up, right? So keep this in mind when we talk about the variable of entropy.
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Entropy Example
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Here, the second law of thermodynamics leads us to conclude what here, the total energy of the universe is constant. No, the second law of thermodynamics doesn't talk about the total energy of the universe. The disorder of the universe is increasing with the passage of time. This is what the second law of thermodynamics discusses that the entropy of my universe changing my energy of my or entropy of my universe is ever increasing. So it's going up, which is what this is saying here, the total energy of the universe is increasing with time. No, not energy entropy, the total entropy of the universe is decreasing. What time? No, that's saying the exact opposite of the second law of thermodynamics. So out of my options, option B is the correct answer.
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Factors Affecting Entropy
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Now, here we're going to say that there are three main factors that can increase my entropy. The first one is my molecular degrees of freedom. This is just the ways in which a molecule is free to move. Here, we say the more ways a molecule can move then the more entropic it is next, a number of arrangements. And this deals with molecular complexity in mass. When we say molecular complexity, it's just the number of atoms in a substance. So for example, let's say it gave us ch four which is methane versus ethane, which is ch three ch three, this has five total atoms in it, one carbon and four hydrogens. And this one here has eight total atoms in it, six hydrogens, two carbons, ethane is more complex. Therefore, it's more entropic, more atoms just needs more arrangements, more ways they can move more ways they can position themselves. Now connected also to this is mass, the greater the mass, the greater the complexity, the more entropic you can be as well. Finally, we can look at the number of moles of substances, more moles, more possibilities, more chaos, more disorder and increase in entropy. So keep in mind these three different factors and how they can themselves increase our entropy overall.
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concept
Standard Molar Entropy
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Now, standard mo of entropy represented by not is the entropy possessed by one mole of a substance at standard conditions. And remember standard conditions means we're at 25 °C and one atmosphere. Now, here's something important to note different phases of a substance can exist simultaneously at standard conditions. For example, water, we know that water exists in its liquid phase predominantly between zero °C and 100 °C. Here, we're at standard conditions of temperature which is 25 °C. Even at that temperature. If you were looking at some liquid water, there would be some water vapor involved even in the room that you're standing in, there's water vapor all around us, we may, may not see it but it exists. And because of that, we can find standard molar entropies of liquid water and gaseous water within our books. Now, solid water though the temperature is too high for it to exist under these standard conditions, so you won't find a standard molar entropy for solid water. Now here, if we're comparing standard mo entropies, we first have to look at the states of matter that are involved if we're going from solid to liquid to gas. We see that the mo molecules are more and more spread out as we transition from solid liquid to gas. Them becoming more spread out means they're more random in their orientation and arrangements and therefore they're more chaotic. This would mean that we're increasing our standard molar entropies here. If they're in the same phase, like you're comparing to solids or comparing two liquids or comparing two gasses, then we look at um what happens when the states of matter are the same. The first thing we do is we look at complexity, we're gonna say the greater the complexity, the greater the standard molar entropy. For example, let's say we're looking at oxygen in the gaseous phase and sulfur in the gaseous phase. Since they're both in the same phase, we then look at their complexity here. A 02 is made up of two atoms of oxygen and S A is made up of eight atoms of sulfur. S eight has more atoms involved. Therefore, it's more chaotic and therefore its standard molar entropy would be higher. But let's say that the two substances that I'm comparing are in the same phase, they have the same complexity. The last thing you look at is mass, the greater the mass, the greater the standard molar entropy. So for example, let's say we're looking at BR two and I two and let's say they both were in the same phase. They're both in the same phase. So next, we look at is our complexity. They both are composed of two atoms. BR two is composed of two atoms of bromine I two is composed of two atoms of iodine. So the tiebreaker would look at their mass, if you look at their molar masses, you would see that I two weighs more than BR two. And because of that I two would be more chaotic and therefore have a higher standard molar entropy. All right. So just remember we can compare the standard molar entropies of different substances by first looking at the phases that they're in gasses have the most entropy followed by liquids, then solids, if they're tied, then look at the complexities. So the number of atoms composed within that substance, if they're still tied, use the mass as the final tiebreaker.
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Entropy Example
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Here to select a substance with greatest more entropy. So remember when comparing the entropies of different substances, the first thing we look at is their phase. So gasses have the most entropy, then liquids then solids. If we take a look at our options here, we have three gasses, they would have the greatest entropy. So that means A is out, B is out and D is out. The next thing we look at to break the tie is their complexity. Basically, the more atoms comprised in the substance, the greater its entropy, ammonia has four atoms involved because it has one nitrogen and three hydrogens, carbon dioxide only has three atoms since it's one carbon and two oxygens. And so for tri I has four atoms because it's one sulfur and three oxygens. So E is out. Now we see that ammonia and sulfur trioxide have the same complexity. So the last thing we look at to break the tie is their mass, the greater the mass of the substance, the greater the entropy here, if we compare the masses of ammonia versus sulfur trioxide, sulfur trioxide weighs more. Therefore, it's gonna have the higher molar entropy. So here. The answer is option F.
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Entropy and Physical Changes
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So here in this video, we're gonna take a look at physical changes and how they can affect the overall change in our entropy. Will it increase our entropy or decrease our entropy? So here we're going to say that entropy change, which is delta S is a measure of the increase or decrease in disorder due to physical or chemical changes. Now we're gonna say an increase in the entropy change is due to an increase in molecular degrees of freedom. So the more movement a substance have has then the greater the change in entropy can be. Now you're going to say the greater the degree of freedom which is molecular motion, this is gonna cause uh the greater the change in entropy. So here let's take a look at changing entropy when it comes to physical changes. All right. So here we have our three major phases of matter, solid liquid and gas. We can say that our entropy increasing means delta S goes up. So how can we play around with temperature and pressure to cause this change? Well, we want more motion, more molecular motion and we should know that at higher temperatures, molecules absorb the excess thermal energy and use it to move themselves even more. So, increasing our temperature can lead to an increase in our entropy. Our change in entropy. What about pressure? Well, if we have our substances within a container with a movable piston, if we push down on that piston, we're increasing the pressure inside of the container. This would cause molecules to come closer and closer together. They're gonna become less disordered because disorder means you're out and about moving anywhere you want, increasing the pressure stops that. So if we want to increase entropy, we wanna decrease our pressure, giving the molecules more space, more freedom of movement. Now here, how do we decrease the change in entropy by doing the exact opposite. If we want to decrease entropy, we force molecules closer together to become more organized. This would happen at higher pressures. And then how do we force molecules to come closer together? We decrease the temperature? So decreasing the temperature would fo force them to come closer and closer together? Think of gaseous water, lower the temperature enough, it'll condense down into a liquid. Liquids have way less freedom of motion than gasses, right. So keep in mind these changes that we can do in terms of temperature and pressure and how they can affect our entropy change.
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Entropy Example
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Predict how the entropy of the system is affected in the following process. Right. So for the first one, we have methane gas at 100 and 25 °C and it's transitioning to methane gas at 200 °C. So the phase of method is still staying the same. But our temperature is increasing, increasing, our temperature would mean that our methane molecules can absorb that extra thermal energy, use it to propel themselves even more, becoming more chaotic, increasing the degrees of freedom. So here increasing temperature would cause an increase it might change in entropy. All right. Next, we have here potassium chlorate solid and it's in a 7 L container. And then we have potassium chlorate liquid in a 3 L container. All right. So changing the volume of the container is a way of affecting the pressure of the container. Remember there's an inverse relationship between pressure and volume. So our volume is going down from 3 L to 7 L, which would mean pressure is going up. But that's kind of a trick question here. Why? Because whether we're looking at what we're starting with and what we're ending, we're dealing with solids and liquids, solids and liquids are not going to be as affected by changes in pressure. At least not something as small as going from a 7 L container to a 3 L container. So what you should really be looking at is the phase change. We're going from solid, potassium chlorate to liquid, potassium chlorate liquids have more degrees of freedom. Their molecules are able to move around more. So because of this change in our phase, there's going to be an increase in the change in entropy. So again, entropy change is going up because we're going from a solid which has less degrees of freedom, less entropy to a liquid which has more degrees of freedom, more movement, more entropy. All right. So in both choices, the change in entropy is increasing.
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concept
Entropy and Chemical Changes
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Now we're looking at chemical changes in order to determine the change in entropy, we're gonna look at it very simplistically, we're gonna say entropy change of chemical reactions are determined by the number of moles of products. So here we take a look in the first image we're talking about increasing our entropy. So that means the change in entropy is going up. If we look at our example, we have one mole of reactant. And then if we look at the number of products, we have two moles of reactant of product, the number of moles of product has gone up. So there's an increase in moles of product, more product being made mean there's more chaos, more disorder, therefore, a higher change in entropy. How about decreasing entropy? Well, here decreasing entropy will mean we're going down in terms of changing entropy. Here, we have initially one mole of nitrogen gas, three moles of hydrogen gas or four total moles. When we transition over to the product side, we only have two moles of product. So we have less moles at the end, which means there's less chaos, less disorder and therefore less entropy. So if there's a decrease in the moles of product. Usually that means that there's going to be a decrease in the change in entropy. So just look at it as simplistically as that is my number of moles going up when I transition to products or is it going down, this will determine the overall change in our entropy. So look at this in this simplistic type of way.
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Entropy Example
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Which one of the following reactions produces a decrease in the entropy of the system. So for a, we're starting out with one mole of solid potassium chloride, it dissolves to produce two moles of, of products. So the number of moles of product has gone up. Therefore, there should be an increase in my change in entropy of my system. So this is not the answer for the next one. We're going from three moles of reactants to just two moles of product. The number of moles of products has decreased. So we've decreased the number of moles going towards the product side. So this would be a decrease in the entropy of my system. Now, let's look at the other options here, we're going from one mole of reactant to uh three moles of product. So the number of moles of product is going up. Therefore, this would be an increase in entropy. Then finding the last one. What do we have here? We have seven moles total of reactants. And over here we have 12 moles of products. So the number of moles has increased as we transition towards the product side, which will cause an increase in my entropy of the system. So out of all the choices, option B represents the one where there's a decrease in the entropy of my system.
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Problem
Problem
Which reaction is most likely to have a positive ∆S of reaction?
a) SiO2 (s) + 3 C (s) → SiC (s) + 2 CO (g)
b) 6 CO2 (g) + 6 H2O (g) → C6H12O6 (s) + 6 O2 (g)
c) CO (g) + Cl2 (g) → COCl2 (g)
d) 3 NO2 (g) + H2O (l) → 2 HNO3 (l) + NO (g)
A
SiO2 (s) + 3 C (s) → SiC (s) + 2 CO (g)
B
6 CO2 (g) + 6 H2O (g) → C6H12O6 (s) + 6 O2 (g)
C
CO (g) + Cl2 (g) → COCl2 (g)
D
3 NO2 (g) + H2O (l) → 2 HNO3 (l) + NO (g)
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Problem
Problem
Identify sign of entropy changes for the following processes.
1) freezing water to form ice
2) ideal gas allowed to expand in a closed container at constant T
3) mixing of two gases into one container
4) NH2 (g) (1atm) → NH2 (g) (3 atm)
5) gas mixture transferred from larger to smaller container
A
1) −∆S, 2) +∆S, 3) +∆S, 4) −∆S, 5) −∆S
B
1) −∆S, 2) −∆S, 3) +∆S, 4) +∆S, 5) −∆S
C
1) +∆S, 2) −∆S, 3) +∆S, 4) −∆S, 5) +∆S
D
1) +∆S, 2) +∆S, 3) −∆S, 4) +∆S, 5) −∆S
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Problem
Problem
Select correct statement(s) below:
a) gaseous CO2 has higher entropy in 2 L container compared to in 5 L container
b) N2O (g) contains higher standard molar entropy then HI (g)
c) NaHCO3 (aq) + HC2H3O2 (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g) has a negative ∆S
d) evaporation of water at 100 °C involves greater ∆S than evaporation at 112 °C
A
gaseous CO2 has higher entropy in 2 L container compared to in 5 L container
B
N2O (g) contains higher standard molar entropy then HI (g)
C
NaHCO3 (aq) + HC2H3O2 (aq) → NaC2H3O2 (aq) + H2O (l) + CO2 (g) has a negative ∆S
D
evaporation of water at 100 °C involves greater ∆S than evaporation at 112 °C