AP Chemistry 9.1-9.6 Basic Overview

### **9.1- Introduction to Entropy**

^^Entropy^^: __dispersal of matter/energy in sample of matter__

* changes of entropy can be seen as how dispersed the matter/energy is
* entropy increases when matter is more dispersed
* (ex. a phase change from solid to liquid, liquid to gas) 
* individual particles at increased entropies are more free to move and occupy more space
* With gases:
* entropy of gas increases when volume, increase because gas molecules are able to move in a larger space with same speed
* if total number of moles of gaseous products>total number of gaseous reactants, entropy increases

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* entropy also increases when energy is more dispersed
* according to KMT, K.E among particles broadens when temperature increases
* entropy increases when temperature increases

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### 9.2- Absolute Entropy and Entropy Change

* entropy change can be calculated from absolute entropies in individual species
* unit: J/K
* most substances have a nonzero value for absolute entropy unlike enthalpy
* when calculating, number of moles of each substance have to be considered

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* ^^**Find delta S with: ΔS=∑S(products)−∑S(reactants)**^^

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* entropy is positive if : phase changes occur as, solid to liquid to gas or if number of moles increase from reactants to products
* entropy is negative if: phase changers occur as, gas to liquid to solid

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### **9.3- Gibbs Free Energy and Thermodynamic Favorability**

^^Gibbs free energy:^^ __△G describes if a reaction is thermodynamically favorable or unfavorable__

^^Thermodynamically favorable:^^ __equation__ __proceeds to equilibrium with no outside factors__

* *reminder! just because reaction is favorable does not mean it happens quickly*

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* in Gibbs free energy all reactants and products are in standard states (pure substance, 1.0M, 1 atm)

^^**Find delta G with: ΔG=∑G(products)−∑G(reactants)**^^

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* thermodynamically favorable, G=negative
* thermodynamically unfavorable, G=positive

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* G can be calculated from enthalpy and entropy with: ^^**ΔG=ΔH-TΔS**^^ \* t=temperature
* if both enthalpy and entropy are favorable or both unfavorable, there is no need to find G to see if its favorable

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### **9.4-Thermodynamic and Kinetic Control**

* processes that are favorable but do not make products at measurable rate, are under kinetic control
* things under kinetic control usually have large activation energy (Ea), making the rate slow down
* a catalyst (ex. enzyme) can decrease Ea and increase reaction rate, but has no effect on favorability 
* even if the process doesn't happen at a noticeable rate, it does not mean it's at not equilibrium

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### 9.5- Free Energy and Equilibrium

* thermodynamically favored (ΔG