# Thermodynamics Flashcard

 Second Law of Thermodynamics
 For any spontaneous process, the entropy of the universe increases (◊Suniv>0)
 Entropy increases (◊S>0) for each of the following:
 The phase transition from a solid to a liquidThe phase transition from a solid to a gasThe phase transition from a liquid to a gasAn increase in the number of moles of a gas during a chemical reaction
 Entropy of the universe, system, and surroundings
 ◊Suniv= ◊Ssys + ◊Ssurr The entropy of the universe must increase (◊Suniv>0) for a process to be spontaneous. The entropy of the system could therefore decrease (◊Ssys<0) as long as the entropy of the surroundings increases by a greater amound (◊Ssurr> -◊Ssys)
 ◊Ssurr = -◊Hsys                  T(at constant T and P)
 ◊Ssurr = -◊Hsys                   T(at constant T and P)
 ◊G = ◊H – T◊S
 ◊G = ◊H – T◊S
 Gibbs Free Energy
 A decrease in Gibbs free energy (◊G < 0) corresponds to a spontaneous process An increase in Gibbs free energy (◊G > 0) corresponds to a nonspontaneous process
 When ◊H is negative and ◊S is positive, is the reaction spontaneous or nonspontaneous?
 It is spontaneous at all temperatures
 When ◊H is positive and ◊S is negative, is the reaction spontaneous or nonspontaneous?
 It is nonspontaneous at all temperatures
 When ◊H and ◊S are both negative, is the reaction spontaneous or nonspontaneous?
 It is spontaneous at low temperatures, but nonspontaneous at high temperatures.
 When ◊H and ◊S are both positive, is the reaction spontaneous or nonspontaneous?
 It is nonspontaneous at low temperatures, and spontaneous at high temperatures.
 The standard state of a substance is defined as follows:
 For a gas: The standard state for a gas is the pure gas at a pressure of exactly 1 atm.For a liquid or solid: The standard state for a liquid or solid is the pure substance in its most stable form at a pressure of 1 atm and the temperature of interest (often taken to be 25 C)For a Substance in Solution: The standard state for a substance in solution is a concentration of exactly 1M.
 Entopies of gases, liquids, and solids:
 The entropy of a gas is generally greater than a liquid, which is in turn greater than the entropy of a solid.gas>liquid>solid
 Entopies related to molar mass:
 Entropy increases with increasing molar mass.
 Entropies related to molar complexity:
 Entropy generally increases with increasing molar complexity
 Entropies related to dissolution:
 The dissolution of a crystalline solid into solution usually results in an increase in entropy.
 Determining ◊G°rxn for a stepwise reaction from the changes in free energy for each of the steps
 If a chemical equation is multiplied by some factor, then ◊Grxn is also multiplied by the same factorIf a chemical equation is reversed, then ◊Grxn changes signIf a chemical equation can be expressed as the sum of a series of steps, then ◊Grxn for the overall equation is the sum of the free energies of reactions for each step.
 The free energy change of a reaction under nonstandard conditions (◊Grxn)
 ◊Grxn = ◊G°rxn + RTlnQ
 ◊G°rxn = -RTlnK
 ◊G°rxn = -RTlnK