Chapter 19 - Entropy & Free Energy

Chapter 19 - Entropy & Free Energy - Entropy, the...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
115 Entropy, the 2 nd Law of Thermodynamics Gibbs Free Energy & the connection to Equilibrium 1 ST Law just keeps track of energy There is a natural direction of physical & chemical processes not explained by the 1 st Law. Eg. 1 A gas expands spontaneously into a vacuum The reverse of this process is never seen though it is allowed by the 1 st law. Eg. 2 Heat flows from a hot body (on the right) to a cold body (on the left). T 1 increases & T 2 decreases until the two systems achieve the same temperature thermal equilibrium Heat never flows the other way, though the 1 st Law would allow it. T 1 T 2 T 1 < T 2 q
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
116 Egs. 3. Spontaneous mixing of gases, miscible liquids, ( natural ) dissolution of soluble salts Random motions of individual molecules leads to irreversible mixing of gases . Methanol & water are miscible - they spontaneously form a solution - a more disordered state when added together. NaCl(s) dissolves spontaneously when added to water - the resulting solution is more disordered than solid salt + water. Though these examples include energy considerations, they illustrate that increasing disorder is a driving force causing some processes to proceed , while prohibiting the reverse Spontaneous mixing of two ideal gases is the best illustration. In this case, interactions between molecules can be neglected (i.e. no energy considerations ), yet the mixing is spontaneous.
Background image of page 2
117 123 an ordered state a disordered state disorder increases In Eg. 2, kinetic energy spreads from the hot body to the cold body. energy is more spread out a more disordered state In Eq. 3, dissolution of salt in water ... the ions have greater freedom in solution - due to increased volume (in comparison to solid) final state has more freedom more disorder In a natural (i.e. spontaneous) process there is a spontaneous increase in disorder . Entropy, S, measures this disorder S increases true for S of entire universe How do we measure "disorder"? or How is S defined?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
118 Consider a deck of cards - continuously reshuffled. If the card shuffler doesn’t cheat , then any ordering of the card is possible the cards are disordered . However, if the card shuffler cheats - eg. producing an ordered deck of cards with each shuffle (eg. always ensuring that the dealer gets a royal flush) the cards are more ordered . supplementary - you are not responsible for the formulae from here to the next dividing line . .. Boltzmann proposed the following formula for entropy in terms of the "number of arrangements of the system which produce the same state" S = k ln W This formula is engraved on Boltzmann's headstone. In the case of the shuffled cards, the "number of arrangements
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 26

Chapter 19 - Entropy &amp;amp; Free Energy - Entropy, the...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online