CHEM 112 1nd EditionExam # 3 Study Guide Lectures: 14-20- If stress is applied to a system at equilibrium, the system is thrown out of equilibrium and shifts in the direction that believes the stress as it goes back to equilibriumo Changes in concentration Does not affect values of K H2 (g) + I2 (g)  2 HI (g) Kc= [HI]2 / [H2] [I2]  What if we added H2?- Q does not equal K, Q < K- Shifts to product side- Lose some of the H2 we added- [I] Decreases, [HI] increases What if we lose some HI?- Lose some of the HI we added- [H2], [I2] increases  What if we remove some I2?- Lose I2- Gain H2- Lose not as much of the I2 as we thoughto Change the size of the container therefore changing the concentration If we increase total pressure on the system, volume of container decreases- Equilibrium shifts toward the side that needs less room (the side that has the few moles of gas)o Change in temperature Changes value of K depending on if reaction is exothermic or endothermic If heat is added, value of K changes If we raise T, adding heat and makes heat a product- The system shifts because K has changed- K decreased when T increaseso Introduction of a catalyst K is unchanged Example- N2 + 3H2  2H3 + 92 kJo Delta H = -92 kJ- We must make more NH3o Lower T (problem: may slow down the reaction)o Increase pressure by decreasing volumeo Increase concentration of N2 and H2o Catalyst does not affect K but will speed up reaction- Other kinds of Ko Kp=pure equilibrium constanto Kp=Kc(RT)change in the number of moles of gas R=0.0821 Latm/molKo K thermo relates to delta G Hybrid of Kc and Kp (aq)-expressed in concentration (g)-expressedin partial pressure- Relationship between delta G and K thermoo Delta G=-RT ln(K thermo)o What if delta G < 0? Reaction spontaneous K will be bigCHAPTER 17: EQUILIBRIUM IN AQUEOUS SOLUTIONS- Storng electrolytes: solute disassociate totally in water- Strong acids: HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4 (dilute—both H+ come off)- Strong soluble bases: IA metal hydroxides, Ba(OH)2, Ca(OH)2, - Soluble saltso IA salt or NH4+ slat, soluableo NO3-, CH3COO-, ClO3-, ClO4- slats are soluble - Weak electrolyteso Weak acids and weak baseso Can be found on back of nomenclature sheet- Ionization of watero H2O (l) + H2O (l)  H30+ (aq) + OH- (aq) H30+ is hydronium ion OH- is hydroxide ion H+ = base protono Kw = [H+] [OH-] = 1 E-14 at 25 degrees C In a neutral solution PH of a neutralizing solution=-log10(1E-7) = 7- At 25 degrees C- Bufferso Weak acids + salts Salt is source of conjugate base Weak acid and base in about same concentrations- 1:10 or 10:1 Best buffering regions is at about ½