All right, guys. So now I want to talk about what I would consider the most confusing term of the Gibbs Free Energy Equation, and that is entropy. All right. So entropy, generally stated, we said that it was a measure of disorder in the system. Okay? But that's a really confusing definition. I would rather go with an easier definition. Okay? And what that is, is that entropy is the tendency of a system to take its most probable form. Okay? So that means that if we have two different states, one is highly ordered and one is not as ordered, statistically, it's more likely to be in the disordered state. Okay? And that's what entropy has to do with. It has to do with probability really. Okay? So what that means is that even if a reaction is highly exothermic, like if you talk about bond dissociation energies and enthalpy, that has to do with exothermic. But the level of order that it requires might make it statistically improbable. Okay? So basically, what we do with entropy is we have to analyze whether this is going to be statistically more probable or statistically less probable. And that is what entropy is. Okay? Remember that we defined that entropy states that a negative value is going to be more ordered because remember that basically a positive value means that it's more disordered. That means that your entropy is getting bigger. So if you have a negative value, that means your entropy is getting smaller or it's getting more ordered. Okay? And it turns out that we're never going to have to calculate the entropy in terms of calculating the entropy of the surrounding environment or the entropy of a system because of the fact that we don't have really the tools to analyze that in orgo 1. Okay? But what you are going to be asked to do, okay, is you're going to be asked to analyze if something is going to have a positive ΔS or negative ΔS. And that's what we want to do. We don't want to figure out the exact number. We just want to figure out whether this is going to have higher entropy or lower entropy. Okay? Now, there is one situation where you might calculate ΔS, and that's if you're given every other variable. If you're given the T and the ΔH and the ΔG, then sure, you could just use algebra to figure out ΔS. But I'm just saying that in the absence of this being just a simple algebra problem, you're not going to be asked just to calculate what the ΔS of an environment. Okay? So let's talk about these three phenomena that make reactions more probable or make ΔS go up. And it turns out that all of them are going to be favored by high temperature. Okay? So that will be that should be really clear in a little bit when I go back to the equation.
- 1. A Review of General Chemistry5h 5m
- Summary23m
- Intro to Organic Chemistry5m
- Atomic Structure16m
- Wave Function9m
- Molecular Orbitals17m
- Sigma and Pi Bonds9m
- Octet Rule12m
- Bonding Preferences12m
- Formal Charges6m
- Skeletal Structure14m
- Lewis Structure20m
- Condensed Structural Formula15m
- Degrees of Unsaturation15m
- Constitutional Isomers14m
- Resonance Structures46m
- Hybridization23m
- Molecular Geometry16m
- Electronegativity22m
- 2. Molecular Representations1h 14m
- 3. Acids and Bases2h 46m
- 4. Alkanes and Cycloalkanes4h 19m
- IUPAC Naming29m
- Alkyl Groups13m
- Naming Cycloalkanes10m
- Naming Bicyclic Compounds10m
- Naming Alkyl Halides7m
- Naming Alkenes3m
- Naming Alcohols8m
- Naming Amines15m
- Cis vs Trans21m
- Conformational Isomers13m
- Newman Projections14m
- Drawing Newman Projections16m
- Barrier To Rotation7m
- Ring Strain8m
- Axial vs Equatorial7m
- Cis vs Trans Conformations4m
- Equatorial Preference14m
- Chair Flip9m
- Calculating Energy Difference Between Chair Conformations17m
- A-Values17m
- Decalin7m
- 5. Chirality3h 39m
- Constitutional Isomers vs. Stereoisomers9m
- Chirality12m
- Test 1:Plane of Symmetry7m
- Test 2:Stereocenter Test17m
- R and S Configuration43m
- Enantiomers vs. Diastereomers13m
- Atropisomers9m
- Meso Compound12m
- Test 3:Disubstituted Cycloalkanes13m
- What is the Relationship Between Isomers?16m
- Fischer Projection10m
- R and S of Fischer Projections7m
- Optical Activity5m
- Enantiomeric Excess20m
- Calculations with Enantiomeric Percentages11m
- Non-Carbon Chiral Centers8m
- 6. Thermodynamics and Kinetics1h 22m
- 7. Substitution Reactions1h 48m
- 8. Elimination Reactions2h 30m
- 9. Alkenes and Alkynes2h 9m
- 10. Addition Reactions3h 18m
- Addition Reaction6m
- Markovnikov5m
- Hydrohalogenation6m
- Acid-Catalyzed Hydration17m
- Oxymercuration15m
- Hydroboration26m
- Hydrogenation6m
- Halogenation6m
- Halohydrin12m
- Carbene12m
- Epoxidation8m
- Epoxide Reactions9m
- Dihydroxylation8m
- Ozonolysis7m
- Ozonolysis Full Mechanism24m
- Oxidative Cleavage3m
- Alkyne Oxidative Cleavage6m
- Alkyne Hydrohalogenation3m
- Alkyne Halogenation2m
- Alkyne Hydration6m
- Alkyne Hydroboration2m
- 11. Radical Reactions1h 58m
- 12. Alcohols, Ethers, Epoxides and Thiols2h 42m
- Alcohol Nomenclature4m
- Naming Ethers6m
- Naming Epoxides18m
- Naming Thiols11m
- Alcohol Synthesis7m
- Leaving Group Conversions - Using HX11m
- Leaving Group Conversions - SOCl2 and PBr313m
- Leaving Group Conversions - Sulfonyl Chlorides7m
- Leaving Group Conversions Summary4m
- Williamson Ether Synthesis3m
- Making Ethers - Alkoxymercuration4m
- Making Ethers - Alcohol Condensation4m
- Making Ethers - Acid-Catalyzed Alkoxylation4m
- Making Ethers - Cumulative Practice10m
- Ether Cleavage8m
- Alcohol Protecting Groups3m
- t-Butyl Ether Protecting Groups5m
- Silyl Ether Protecting Groups10m
- Sharpless Epoxidation9m
- Thiol Reactions6m
- Sulfide Oxidation4m
- 13. Alcohols and Carbonyl Compounds2h 17m
- 14. Synthetic Techniques1h 26m
- 15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
- Purpose of Analytical Techniques5m
- Infrared Spectroscopy16m
- Infrared Spectroscopy Table31m
- IR Spect:Drawing Spectra40m
- IR Spect:Extra Practice26m
- NMR Spectroscopy10m
- 1H NMR:Number of Signals26m
- 1H NMR:Q-Test26m
- 1H NMR:E/Z Diastereoisomerism8m
- H NMR Table24m
- 1H NMR:Spin-Splitting (N + 1) Rule22m
- 1H NMR:Spin-Splitting Simple Tree Diagrams11m
- 1H NMR:Spin-Splitting Complex Tree Diagrams12m
- 1H NMR:Spin-Splitting Patterns8m
- NMR Integration18m
- NMR Practice14m
- Carbon NMR4m
- Structure Determination without Mass Spect47m
- Mass Spectrometry12m
- Mass Spect:Fragmentation28m
- Mass Spect:Isotopes27m
- 16. Conjugated Systems6h 13m
- Conjugation Chemistry13m
- Stability of Conjugated Intermediates4m
- Allylic Halogenation12m
- Reactions at the Allylic Position39m
- Conjugated Hydrohalogenation (1,2 vs 1,4 addition)26m
- Diels-Alder Reaction9m
- Diels-Alder Forming Bridged Products11m
- Diels-Alder Retrosynthesis8m
- Molecular Orbital Theory9m
- Drawing Atomic Orbitals6m
- Drawing Molecular Orbitals17m
- HOMO LUMO4m
- Orbital Diagram:3-atoms- Allylic Ions13m
- Orbital Diagram:4-atoms- 1,3-butadiene11m
- Orbital Diagram:5-atoms- Allylic Ions10m
- Orbital Diagram:6-atoms- 1,3,5-hexatriene13m
- Orbital Diagram:Excited States4m
- Pericyclic Reaction10m
- Thermal Cycloaddition Reactions26m
- Photochemical Cycloaddition Reactions26m
- Thermal Electrocyclic Reactions14m
- Photochemical Electrocyclic Reactions10m
- Cumulative Electrocyclic Problems25m
- Sigmatropic Rearrangement17m
- Cope Rearrangement9m
- Claisen Rearrangement15m
- 17. Ultraviolet Spectroscopy51m
- 18. Aromaticity2h 34m
- 19. Reactions of Aromatics: EAS and Beyond5h 1m
- Electrophilic Aromatic Substitution9m
- Benzene Reactions11m
- EAS:Halogenation Mechanism6m
- EAS:Nitration Mechanism9m
- EAS:Friedel-Crafts Alkylation Mechanism6m
- EAS:Friedel-Crafts Acylation Mechanism5m
- EAS:Any Carbocation Mechanism7m
- Electron Withdrawing Groups22m
- EAS:Ortho vs. Para Positions4m
- Acylation of Aniline9m
- Limitations of Friedel-Crafts Alkyation19m
- Advantages of Friedel-Crafts Acylation6m
- Blocking Groups - Sulfonic Acid12m
- EAS:Synergistic and Competitive Groups13m
- Side-Chain Halogenation6m
- Side-Chain Oxidation4m
- Reactions at Benzylic Positions31m
- Birch Reduction10m
- EAS:Sequence Groups4m
- EAS:Retrosynthesis29m
- Diazo Replacement Reactions6m
- Diazo Sequence Groups5m
- Diazo Retrosynthesis13m
- Nucleophilic Aromatic Substitution28m
- Benzyne16m
- 20. Phenols55m
- 21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
- Naming Aldehydes8m
- Naming Ketones7m
- Oxidizing and Reducing Agents9m
- Oxidation of Alcohols28m
- Ozonolysis7m
- DIBAL5m
- Alkyne Hydration9m
- Nucleophilic Addition8m
- Cyanohydrin11m
- Organometallics on Ketones19m
- Overview of Nucleophilic Addition of Solvents13m
- Hydrates6m
- Hemiacetal9m
- Acetal12m
- Acetal Protecting Group16m
- Thioacetal6m
- Imine vs Enamine15m
- Addition of Amine Derivatives5m
- Wolff Kishner Reduction7m
- Baeyer-Villiger Oxidation39m
- Acid Chloride to Ketone7m
- Nitrile to Ketone9m
- Wittig Reaction18m
- Ketone and Aldehyde Synthesis Reactions14m
- 22. Carboxylic Acid Derivatives: NAS2h 51m
- Carboxylic Acid Derivatives7m
- Naming Carboxylic Acids9m
- Diacid Nomenclature6m
- Naming Esters5m
- Naming Nitriles3m
- Acid Chloride Nomenclature5m
- Naming Anhydrides7m
- Naming Amides5m
- Nucleophilic Acyl Substitution18m
- Carboxylic Acid to Acid Chloride6m
- Fischer Esterification5m
- Acid-Catalyzed Ester Hydrolysis4m
- Saponification3m
- Transesterification5m
- Lactones, Lactams and Cyclization Reactions10m
- Carboxylation5m
- Decarboxylation Mechanism14m
- Review of Nitriles46m
- 23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
- 24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
- Tautomerization9m
- Tautomers of Dicarbonyl Compounds6m
- Enolate4m
- Acid-Catalyzed Alpha-Halogentation4m
- Base-Catalyzed Alpha-Halogentation3m
- Haloform Reaction8m
- Hell-Volhard-Zelinski Reaction3m
- Overview of Alpha-Alkylations and Acylations5m
- Enolate Alkylation and Acylation12m
- Enamine Alkylation and Acylation16m
- Beta-Dicarbonyl Synthesis Pathway7m
- Acetoacetic Ester Synthesis13m
- Malonic Ester Synthesis15m
- 25. Condensation Chemistry2h 9m
- 26. Amines1h 43m
- 27. Heterocycles2h 0m
- Nomenclature of Heterocycles15m
- Acid-Base Properties of Nitrogen Heterocycles10m
- Reactions of Pyrrole, Furan, and Thiophene13m
- Directing Effects in Substituted Pyrroles, Furans, and Thiophenes16m
- Addition Reactions of Furan8m
- EAS Reactions of Pyridine17m
- SNAr Reactions of Pyridine18m
- Side-Chain Reactions of Substituted Pyridines20m
- 28. Carbohydrates5h 53m
- Monosaccharide20m
- Monosaccharides - D and L Isomerism9m
- Monosaccharides - Drawing Fischer Projections18m
- Monosaccharides - Common Structures6m
- Monosaccharides - Forming Cyclic Hemiacetals12m
- Monosaccharides - Cyclization18m
- Monosaccharides - Haworth Projections13m
- Mutarotation11m
- Epimerization9m
- Monosaccharides - Aldose-Ketose Rearrangement8m
- Monosaccharides - Alkylation10m
- Monosaccharides - Acylation7m
- Glycoside6m
- Monosaccharides - N-Glycosides18m
- Monosaccharides - Reduction (Alditols)12m
- Monosaccharides - Weak Oxidation (Aldonic Acid)7m
- Reducing Sugars23m
- Monosaccharides - Strong Oxidation (Aldaric Acid)11m
- Monosaccharides - Oxidative Cleavage27m
- Monosaccharides - Osazones10m
- Monosaccharides - Kiliani-Fischer23m
- Monosaccharides - Wohl Degradation12m
- Monosaccharides - Ruff Degradation12m
- Disaccharide30m
- Polysaccharide11m
- 29. Amino Acids3h 20m
- Proteins and Amino Acids19m
- L and D Amino Acids14m
- Polar Amino Acids14m
- Amino Acid Chart18m
- Acid-Base Properties of Amino Acids33m
- Isoelectric Point14m
- Amino Acid Synthesis: HVZ Method12m
- Synthesis of Amino Acids: Acetamidomalonic Ester Synthesis16m
- Synthesis of Amino Acids: N-Phthalimidomalonic Ester Synthesis13m
- Synthesis of Amino Acids: Strecker Synthesis13m
- Reactions of Amino Acids: Esterification7m
- Reactions of Amino Acids: Acylation3m
- Reactions of Amino Acids: Hydrogenolysis6m
- Reactions of Amino Acids: Ninhydrin Test11m
- 30. Peptides and Proteins2h 42m
- Peptides12m
- Primary Protein Structure4m
- Secondary Protein Structure17m
- Tertiary Protein Structure11m
- Disulfide Bonds17m
- Quaternary Protein Structure10m
- Summary of Protein Structure7m
- Intro to Peptide Sequencing2m
- Peptide Sequencing: Partial Hydrolysis25m
- Peptide Sequencing: Partial Hydrolysis with Cyanogen Bromide7m
- Peptide Sequencing: Edman Degradation28m
- Merrifield Solid-Phase Peptide Synthesis18m
- 31. Catalysis in Organic Reactions1h 30m
- 32. Lipids 2h 50m
- 34. Nucleic Acids1h 32m
- 35. Transition Metals5h 33m
- Electron Configuration of Elements45m
- Coordination Complexes20m
- Ligands24m
- Electron Counting10m
- The 18 and 16 Electron Rule13m
- Cross-Coupling General Reactions40m
- Heck Reaction40m
- Stille Reaction13m
- Suzuki Reaction25m
- Sonogashira Coupling Reaction17m
- Fukuyama Coupling Reaction15m
- Kumada Coupling Reaction13m
- Negishi Coupling Reaction16m
- Buchwald-Hartwig Amination Reaction19m
- Eglinton Reaction17m
- 36. Synthetic Polymers1h 49m
- Introduction to Polymers6m
- Chain-Growth Polymers10m
- Radical Polymerization15m
- Cationic Polymerization8m
- Anionic Polymerization8m
- Polymer Stereochemistry3m
- Ziegler-Natta Polymerization4m
- Copolymers6m
- Step-Growth Polymers11m
- Step-Growth Polymers: Urethane6m
- Step-Growth Polymers: Polyurethane Mechanism10m
- Step-Growth Polymers: Epoxy Resin8m
- Polymers Structure and Properties8m
Entropy: Study with Video Lessons, Practice Problems & Examples
Entropy is a measure of disorder, reflecting a system's tendency to adopt its most probable state. Reactions that increase the number of molecules, undergo phase transitions, or enhance molecular freedom of motion are entropically favored, especially at high temperatures. For example, thermal cracking breaks large hydrocarbons into smaller ones, increasing entropy. The Gibbs Free Energy equation, ΔG = ΔH - TΔS, shows that as temperature (T) rises, the significance of entropy (ΔS) in determining spontaneity increases, making reactions more favorable.
If a reaction is exothermic, shouldn’t that be enough to determine favorability? Actually, no!
Even if a reaction is highly exothermic, the level of order it requires may make it statistically improbable.
Explaining what entropy is.
Video transcript
Entropy (ΔS) is the tendency of a system to take its most probable form.
- Negative values (-) indicate less probable = Unfavored
- Positive values (+) indicate more probable = Favored
There are 3 common ways to make reactions more probable (increase ΔS)
- They all become more likely as we add heat to the reaction (increase T)
3 ways to increase entropy.
Video transcript
The first one is increasing the number of molecules in a reaction. Okay? So, any reaction that's going to make more moles of molecules or more equivalents of molecules after the reaction is over is going to be entropically favored. Why? Because what it does is it allows us to arrange these molecules in more ways. Alright? So here's a really good example, thermal cracking. Okay? This is used by the petroleum industry to take large hydrocarbons, ones that don’t really do anything. You can't put them in your car or anything. Then they put them with hydrogen in high heat. Okay? And what happens is that these long hydrocarbons spontaneously start breaking into smaller pieces. Okay? Why would this be a favored reaction? Okay? It actually takes energy to break those bonds, so why would these long hydrocarbons break? The reason is that at high enough temperature, what starts to happen is that if we can break 1 molecule into 10 molecules, right? That's going to be entropically favored because now I can arrange those molecules in different orders. Okay? So what that means is the chances are that if I have 2 systems that of equal scattered all over the place. Which one is going to be more probable? The one where it's scattered all over the place. Which one's going to be more probable? The one where it’s scattered. Okay? And that's why thermal cracking is favored. You take large hydrocarbons and you turn them into smaller ones by using high heat. High heat then makes the entropy part of the equation very, very favored. So now, the more pieces I can break it into, the more entropically favored that is. Alright? This is just one example, but there's lots of examples in organic chemistry of reactions that make more molecules than they start off with, meaning that they're entropically favored. Okay? So let's go on to the second one. The second one is a phase transition. Okay? If I can transform something from a solid to a liquid or from a liquid to a gas, that's going to be a more probable arrangement. The reason is because the molecules are now going to have greater vibrational freedom. Remember, the only difference between a solid, liquid, and gas is how much energy these molecules have. Okay? And how much motion they’re allowed to display. In a solid, there's very little vibration that can happen. They can only move in a very constrained space. K? Whereas in a gas, they're bouncing all over the place. For example, the gas in this room right now, it's bouncing off the walls, it's hitting me. That has a lot more freedom of motion than a solid does. So if I have 2 systems of equal energy, one where my molecules are constrained to one tiny little place next to another one, and then another system where the molecules can scatter as far as they want, which one is more favored? The one that they can scatter in. Okay? So what that means is that we have reactions that as you turn liquids into gases or solids into liquids, they're also entropically favored. A really good example is a reaction that we're going to learn in Orgo 2 called decarboxylation. Decarboxylation takes a carboxylic acid at high heat and it turns it into just a ketone and CO2 gas. Why is that favored? Because at high heat, now the entropy part of my equation becomes more powerful. It gets a higher weight. Okay? And if I’m turning something into a gas, that’s going to be more favored because a gas is more favored than a liquid. Okay? And by the way, this molecule right here would be a liquid at room temperature. Okay? Now, another thing to keep in mind is that this is also favored because of another thing, which is this is also favored by the making more molecules rule. Remember that here I have one molecule total. At the end of the equation, I have 1 molecule here and 1 molecule here, so I’m going from 1 mole to 2 moles of molecules. So what that means is that this is also going to be entropically favored not just because of the phase transition but also because I’m making a greater number of molecules. Alright? So let’s look at the last one. The last one is increasing, freedom of motion of a molecule. Okay? And this specifically has to do with cyclic molecules. If I can convert a cyclic molecule into an acyclic molecule, that's going to be more probable because now it's going to increase the freedom of rotation of these carbon chains. So this is also a reaction that you're going to see a lot in Orgo 2, lactone ring opening. Okay? A lactone is just a cyclic ester. Okay? That's the name of a lactone. We’re going to talk about that a lot more in orgo 2. What you see here is that in the presence of heat, what I can do is I can take my lactone and I can break the chain, the ring apart into 2 parts of the chain where this oxygen and this oxygen were linked together before and basically were the same thing. Okay? Now, what I do is I put 1 oxygen on each and now I have my carbon chain that has more freedom of motion. Now why is the chain better than the ring? Because remember when we talked about if remember when we talked about conformers and we talked about single bonds being able to rotate. Okay? What would happen is that these single bonds can all rotate a lot more than a ring. In a ring, you actually can't rotate at all. So what that means is that this one is going to have a whole lot more conformers possible than the first one. In fact, the first one doesn’t have any. Okay? That’s also more probable because if you have 2, molecules of equal energy and you have one where all of the bonds are eclipsed, that’s what this would be. This would be all eclipsed. Okay? If you have one where all the H's are eclipsed and then you have another one where they’re free to rotate and make anti and make gauche and make a bunch of different conformations. Which one's going to be more favored? The one on this side. So this one's also going to be entropically favored to open that ring as I increase the heat. As I jack up the heat more, that’s going to favor all of these reactions. And like I said, the reason has to do with Gibbs free energy. And remember that Gibbs free energy just basically stated that ΔG=ΔH-TΔS. So what that means is that as I increase T, what I'm going to do is I'm going to increase the amount that entropy matters. Okay? So if I raise all these reactions to a 1000 degrees, the enthalpy isn't even going to matter anymore. I'm not going to care about bond association energies because instead what I'm going to care about is how many molecules am I getting at the end or what's the freedom of rotation of these molecules. Interesting. That's going to tell us which one's more statistically favored and that’s going to be which one is more spontaneous. Alright?
1. Increasing the Number of Molecules
Reactions that create extra molecules are more probable since there are more ways to arrange them.
2. Phase Transition
Transformation of solid to liquid or liquid to gas is more probable since the molecules will have a greater vibrational freedom.
3. Increasing Molecular Freedom of Motion
Converting cyclic molecules to acyclic molecules are more probable since it increases freedom of rotation.
Do you want more practice?
More setsHere’s what students ask on this topic:
What is entropy in chemistry?
Entropy in chemistry is a measure of disorder or randomness in a system. It reflects the tendency of a system to adopt its most probable state. In simpler terms, entropy quantifies the number of ways a system can be arranged. Higher entropy means more disorder and more possible arrangements. For example, gases have higher entropy than liquids, and liquids have higher entropy than solids. The concept of entropy is crucial in understanding the spontaneity of chemical reactions, as described by the Gibbs Free Energy equation:
How does temperature affect entropy?
Temperature significantly affects entropy. As temperature increases, the entropy of a system generally increases because the molecules have more kinetic energy and can occupy more possible states. This is particularly evident in phase transitions, such as when a solid melts into a liquid or a liquid evaporates into a gas. Higher temperatures make these transitions more likely, increasing the system's entropy. In the Gibbs Free Energy equation
What is the relationship between entropy and Gibbs Free Energy?
The relationship between entropy and Gibbs Free Energy is described by the equation:
Why are phase transitions entropically favored?
Phase transitions are entropically favored because they increase the disorder and the number of possible arrangements of molecules. For example, when a solid melts into a liquid or a liquid evaporates into a gas, the molecules gain more freedom of motion and can occupy more states. This increase in molecular freedom and possible arrangements leads to higher entropy. In the context of the Gibbs Free Energy equation
How does increasing the number of molecules in a reaction affect entropy?
Increasing the number of molecules in a reaction generally increases the entropy of the system. This is because more molecules mean more possible ways to arrange them, leading to greater disorder. For example, in thermal cracking, large hydrocarbons are broken down into smaller molecules, increasing the total number of molecules. This increase in the number of molecules results in higher entropy, making the reaction entropically favored. In the Gibbs Free Energy equation
Your Organic Chemistry tutors
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