General Chemistry II - Exam 3
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20 terms
Chemistry | Math / Symbols |
|---|---|
 Entropy | (S), a thermodynamic function that increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular state. |
| S = k·ln(W) | Equation for entropy, where k is the Boltzmann constant (the gas constant divided by Avogadro's number, 1.38×10⁻²³J/K) and W is the number of energetically equivlent ways to arrange the components of the system. |
| ∆S = Sfinal - Sinitial | The change in entropy is simply the entropy of the final state minus the entropy of the initial state. A chemical system proceeds in a direction that increases the entropy of the universe-- it proceeds in a direction that has the largest number of energetically equivalent ways to arrange its components. |
| Second Law of Thermodynamics | For any spontaneous process, the entropy of the universe increases (∆Suniverse > 0). |
| Summary of Entropy Change Associated with a Change in State | In general, entropy increases (∆S > 0) for each of the following: -The phase transition from a solid to a liquid -The phase transition from a solid to a gas -The phase transition from a liquid to a gas -An increase in the number of moles of a gas during a chemical reaction |
| ∆Suniverse = ∆Ssystem + ∆Ssurroundings | The entropy of the universe must increase for a process to spontaneous. -An exothermic process increases the entropy of the surroundings. -An endothermic process decreases the entropy of the surroundings. |
| ∆Ssurr = (-∆Hsys) / T | Equation for calculating entropy changes in the surroundings |
| Gibbs Free Energy | (G), a thermodynamic state function related to enthalpy and entropy by the equation G = H - TS; chemical systems tend towards lower Gibbs free energy, also called the "chemical potential". |
| ∆G = ∆H + T∆S | formula for determining the change in free energy; where ∆G=change in free energy, ∆H=change in total energy (enthalpy), T=temp in K, ∆S=change in entropy |
| Summary of Gibbs Free Energy at Constant Temperature and Pressure | -∆G is proportional to the negative of ∆Suniverse -A decrease in Gibbs free energy (∆G < 0) corresponds to a spontaneous process. -An increase in Gibbs free energy (∆G > 0) corresponds to a non-spontaneous process. |
| Gibbs Free Energy: -∆H, +∆S | Low Temperature: Spontaneous (∆G < 0) High Temperature: Spontaneous (∆G < 0) |
| Gibbs Free Energy: +∆H, -∆S | Low Temperature: Non-spontaneous (∆G > 0) High Temperature: Non-spontaneous (∆G > 0) |
| Gibbs Free Energy: -∆H, -∆S | Low Temperature: Spontaneous (∆G < 0) High Temperature: Non-spontaneous (∆G > 0) |
| Gibbs Free Energy: +∆H, +∆S | Low Temperature: Non-spontaneous (∆G > 0) High Temperature: Spontaneous (∆G < 0) |
| Rules for ∆G | (∆G is similar to ∆H!) -If the reaction is multiplied by a factor, ∆G is multiplied by the same factor. -If the reaction is reversed, then the sign (+/-) of ∆G is reversed. -If a reaction is expressed as a series of steps, ∆Grxn = ∑∆Gsteps. |
| ∆Grxn = ∆G°rxn + RTln(Q) | Formula for calculating nonstandard states of Gibbs Free Energy (∆Grxn), where Q is the reaction quotient. |
| ∆G°rxn = -RTln(K) | rearranged: K = e^((∆G°rxn)/(-RT)) |
| ln(K) = ((-∆H°rxn)/R)(1/T)+((∆S°rxn)/R) | ... |
| ∆G°rxn = ∑npGf°p - ∑nrGf°r | ... |
| ∆S°rxn = ∑npS°p - ∑nrS°r | ... |
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