Entropy: Embrace the Chaos! Crash Course Chemistry #20

CrashCourse
1 Jul 201313:40
EducationalLearning
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TLDRThe video explains that according to the second law of thermodynamics, the natural tendency of the universe is toward disorder, or entropy. It states that spontaneous chemical reactions increase randomness and require no outside energy input. The change in Gibbs free energy (G) determines if a reaction will occur spontaneously - a negative Ξ”G means the reaction is spontaneous. An endothermic reaction that absorbed heat yet froze surrounding water is analyzed; though counterintuitive, math shows the large increase in entropy drove the reaction, not the heat change. Josiah Willard Gibbs' equation relating enthalpy, entropy, temperature and free energy is introduced to calculate and confirm the reaction's spontaneity.

Takeaways
  • 😟 Everything tends toward chaos and disorder due to probability.
  • 😨 The second law of thermodynamics states that the disorder of the universe always increases.
  • 😞 Increasing order requires energy and creates disorder elsewhere.
  • 🀯 Entropy measures molecular randomness and disorder.
  • 😎 Entropy helps explain how some reactions occur spontaneously without energy input.
  • πŸ˜€ Gibbs free energy measures usable work available from a reaction.
  • 🧠 Gibbs created an equation relating free energy to enthalpy and entropy changes.
  • πŸ“‰ Negative Gibbs free energy change means a reaction is spontaneous.
  • πŸ” Both enthalpy and entropy changes determine Gibbs free energy.
  • πŸŽ“ Understanding entropy and free energy explains counterintuitive spontaneous reactions.
Q & A

  • Why does the universe tend toward disorder?

    -It's due to simple rules of probability - there are many more disorganized states than organized ones for things to be arranged in, so it's more likely for stuff to end up disorganized.

  • What does the Second Law of Thermodynamics state?

    -It states that any spontaneous process increases the disorder or randomness of the universe.

  • What does 'spontaneous' mean in chemistry?

    -In chemistry, 'spontaneous' doesn't refer to the speed of a reaction but rather means a reaction is thermodynamically capable of occurring without needing an input of external energy.

  • How is entropy calculated?

    -Entropy is calculated by subtracting the sum of the reactant entropies from the sum of the product entropies, similar to how enthalpy change is calculated.

  • What does Gibbs free energy tell us?

    -Gibbs free energy, or G, tells us how much energy in a system is free and available to do useful work. The change in Gibbs free energy (Delta G) can also tell us if a reaction is spontaneous.

  • When is a reaction considered enthalpy-driven?

    -A reaction is enthalpy-driven when the heat transfer (enthalpy change) provides more free energy than the increase in disorder (entropy change).

  • When is a reaction considered entropy-driven?

    -A reaction is entropy-driven when the increase in disorder (entropy change) provides more free energy than the heat transfer (enthalpy change).

  • Why was the example reaction with barium hydroxide spontaneous?

    -The reaction had a large increase in entropy as it went from solid reactants to liquid and gaseous products, giving it enough free energy from increased disorder to be spontaneous.

  • How do you know if Delta G makes a reaction spontaneous?

    -If Delta G is negative, the reaction releases free energy and is spontaneous. If Delta G is positive, the reaction requires free energy input to proceed.

  • What are the key things the video explains about thermodynamics?

    -It explains entropy, spontaneity, Gibbs free energy, enthalpy vs. entropy driven reactions, and how to use Delta G to predict spontaneity.

Outlines
00:00
😟 The Second Law of Thermodynamics - Things Tend Toward Chaos and Disorder

Paragraph 1 discusses the inevitability of chaos and disorder in the universe. It introduces the Second Law of Thermodynamics which states that the entropy or disorder of the universe always increases for spontaneous processes. Examples are provided related to food molecules breaking down and house cleaning to illustrate how bringing order to one system results in greater disorder elsewhere.

05:03
πŸ€” An Entropy-Driven Chemical Reaction That Feels Cold

Paragraph 2 demonstrates an entropy-driven chemical reaction between barium hydroxide and ammonium chloride that absorbs heat from its surroundings, feels cold, and freezes wood. Calculations show the reaction increases entropy more than it changes enthalpy, confirming it is entropy-driven.

10:04
😎 Gibbs Free Energy Explains Spontaneity of Entropy-Driven Reactions

Paragraph 3 introduces Gibbs free energy, calculated from changes in enthalpy and entropy. The reaction from Paragraph 2 is shown to have negative Gibbs free energy, making it spontaneous even though it absorbed heat. This confirms reactions can happen spontaneously by increasing entropy rather than releasing heat.

Mindmap
Keywords
πŸ’‘entropy
Entropy is a measure of disorder or randomness in a system. The video explains how the second law of thermodynamics states that entropy increases over time in the universe and in chemical reactions. More disorder allows more ways for energy and particles to be arranged.
πŸ’‘spontaneous process
A spontaneous process is one that occurs without needing an input of energy from outside the system. The video gives examples like reactions, phase changes, and physical changes that increase entropy and thus can occur spontaneously.
πŸ’‘Gibbs free energy
Also called standard free energy, Gibbs free energy represents the amount of energy available to do useful work in a system. The video explains how to calculate it using enthalpy, entropy, and temperature. The sign of Gibbs free energy indicates if a process is spontaneous.
πŸ’‘enthalpy
Enthalpy refers to the heat content or thermal energy in a chemical system. Changes in enthalpy show whether heat is released or absorbed in a reaction. This contributes to calculating Gibbs free energy.
πŸ’‘entropy-driven reaction
A reaction where the increase in entropy or disorder is the dominant factor allowing it to proceed spontaneously, more so than enthalpy effects. The example reaction with barium hydroxide is entropy-driven.
πŸ’‘state function
A property that depends only on the current state of a system, not the pathway to reach that state. Enthalpy, entropy and Gibbs free energy are state functions used to describe chemical systems and reactions.
πŸ’‘second law of thermodynamics
A fundamental natural law stating that the entropy of the universe always increases over time. The video uses this to explain why disorder, decay, and randomness occur in the natural world and chemistry.
πŸ’‘disorder
Lack of order or organization at the molecular level. Entropy is a quantitative measure of disorder in chemistry. The video explores how molecular disorder underpins messy real-world systems.
πŸ’‘standard entropy
The absolute entropy value for a pure substance in its standard state. Used along with standard enthalpies to calculate entropy and Gibbs free energy changes in chemical reactions.
πŸ’‘standard free energy change
The change in Gibbs free energy for a system undergoing a chemical reaction under standard state conditions. Its sign and value determine if the reaction occurs spontaneously.
Highlights

The universe tends toward disorder due to simple rules of probability.

Entropy is a measure of molecular randomness or disorder.

The Second Law of Thermodynamics states that any spontaneous process increases the disorder of the universe.

In chemistry, "spontaneous" refers to reactions that can occur without added energy, not the speed of the reaction.

Entropy helps explain how some reactions can occur spontaneously even though they absorb energy.

Gibbs free energy measures the energy available to do useful work.

Gibbs created a formula to calculate free energy change from enthalpy and entropy changes.

Enthalpy change refers to heat transfer; entropy change refers to disorder created.

If enthalpy change outweighs TΞ”S, the reaction is enthalpy-driven. If TΞ”S outweighs enthalpy change, the reaction is entropy-driven.

Negative Ξ”G means the reaction releases free energy, indicating it is spontaneous.

The example reaction absorbed heat but was entropy-driven due to the large increase in disorder going from solids to liquids/gases.

The reaction was spontaneous because Gibbs free energy was negative, indicating free energy was released.

Even though the reaction absorbed heat, the large entropy change made it spontaneous without added energy.

Gibbs' formula shows whether a reaction is spontaneous based on the sign of Ξ”G.

The key things learned are entropy always increases, Gibbs' formula relates entropy and enthalpy to spontaneity, and the sign of Ξ”G indicates spontaneity.

Transcripts

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