Chem 108 Exam 2 study guide Chemistry conquistador Chapter 15 Chemical equilibrium o Rate f kf NO2 2 o Rate r kr N2O4 o kf NO2 2 kr N2O4 k1 k2 A B Constant K Chemical equilibrium Dynamic process in which the concentrations of reactants and produces remain constant over time At equilibrium Reaction 2 NO g N2O4 g Also the rate of its forward reaction is equal to the rate its backward reaction Equilibrium Constant Expression Ratio of equilibrium concentrations or partial pressures of products to reactants each term raised to a power equal to the coefficient of that substance in the balanced chemical equation K C c D d A a B b Products reactants o where A B etc are equilibrium concentrations could also be partial pressure K 1 equilibrium lies to the right the concentration of the products is greater than the K 1 equilibrium lies to the left the concentration of the reactants is greater than the concentration of the reactants concentration of the products The Molar concentrations of pure liquids and solids are not in the equilibrium constant expression because those concentrations stay constant K 0 no reaction Kf 1 Kr Reaction Quotient Q The K constant of reactions is only when the reaction is in equilibrium When it is not in equilibrium the value becomes the reaction quotient Q C c D d A a B b o Q K reaction goes left to right favors the products forward reaction To get to equilibrium must add more reactants o Q K reaction goes right to left favors the reactants reverse reaction To get to equilibrium must add more products o Q K reaction is at equilibrium o With this you can predict where the reaction is going to go Equilibrium in the Gas Phase Kp Kc RT n Kp Kc RT Le Ch telier s Principle A system at equilibrium responds to a stress in such a way that it relieves that stress Factors that will change the relative rates of forward reverse reactions or change the value of Q compared to K will cause a shift in the position of equilibrium If you add or take away products or reactants the reaction would shift until equilibrium was reached o Ex H2O g CO g H2 g CO2 g o Rate of reverse reaction decreases reaction proceeds in forward direction to Remove CO2 g establish new equilibrium o Q H2 CO2 H2O CO o Removing CO2 Q K reaction shifts right toward products Effects of Temperature and pressure on equilibrium The value of K for an endothermic reaction increases with increasing temperature and the value of K for an exothermic reaction decreases with increasing temperature Equilibrium shifts in response to an increase or decrease in volume caused by a decrease or increase in pressure toward the side with fewer moles of gases Calculating concentrations partial pressures of reactants and products Use the I C E table to develop algebraic terms for each reactants and products concentration partial pressure at equilibrium Let x be the change in concentration partial pressure of each component of the reaction Express the changes in terms of x and substitute these terms into the expression for K and solve for x Quadratic equation Chapter 16 Acid Base and Solubility Equilibrium Arrhenius Acids and Bases Arrhenius acid an Arrhenius acid will increase proton concentration in water Arrhenius base an Arrhenius base will increase hydroxide concentration in water Br nsted Lowry Model Br nsted Lowry acid H ion donor Br nsted Lowry base H ion acceptor NH3 aq H2O l NH4 Water can act as both a Br nsted Lowry acid and base aq OH aq H2O is acid NH3 is base o H2O H2O H3O OH Lewis Acids and Bases Lewis acid electron pair acceptor Lewis base electron pair donor H and OH do not necessarily have to be involved Electron pairs of one reactant the Lewis base attracted to positively charged regions of another reactant the Lewis acid o positively charged transition metal ions act as Lewis acids Acid Ionization Constant Ka Acid strength is measured by the size of the equilibrium constant when it reacts with H2O o HAcid H2O Acid H3O The equilibrium constant for this reaction is called the acid ionization constant Ka o Ka Acid H3O HAcid H2O o strong acids completely ionized in water Strong acids Ka 1 o weak acids only partially ionized in water Weak Acids Ka 1 Conjugate acid base pairs Differ from each other only by the presence or absence of a proton o The strongest acid have the weakest conjugate base o The weakest acid has the strongest conjugate base o But in between there are weak acids that are paired with weak bases The pH Scale Quantitative measure of acidity pH log H where H is in M o Strong acids have a lower pH since strong acids fully dissociate in water so it increases the H concentration and decreases the pH o lower pH stronger acid weaker base o higher pH weaker acid stronger base o Usually pH defined for aqueous solutions pOH log OH Kw 1 10 14 H OH o Log form of Kw log Kw log H OH Concentration of H OH Solution is neutral 14 00 pH pOH pK A way of expressing the strength of an acid or base pKa log Ka Ka 10 pKa o The stronger the acid the smaller the pKa o larger Ka smaller pKa because it is the log Calculating pH of o strong acid H Acid initial o Weak acid H calculated by solving equilibrium equation using I C E table Once we have the equilibrium concentrations we can find the pH because we have H concentration o Obtain OH at equilibrium using I C E table then use Kw relationship to find the concentration of H for the pH Polyprotic acid Polyprotic acid can donate more than one proton There is a different value of Ka for each ionizable level o Ka1 Ka2 Ka3 More difficult to remove H ion positive charge from negatively charged anion pH of Polyprotic acid solutions Typically only first ionizable H atom affects pH Ka1 F aq H2O l HF aq OH aq pH of salt solutions Determine Ka or Kb o Kb HF OH F using I C E tables o pOH log OH o pH pKw pOH pKw 14 By Solving equilibrium problem for H OH you can determine pH of the solution Aqueous solutions of salts can be acidic basic or neutral To predict dissociate salt and determine if cations and anions are acids bases or neutral o conjugate bases of strong acids are neutral o conjugate acids of strong bases are neutral o conjugate bases of weak acids are weak bases o conjugate acids of weak bases are weak acids Ex NaCl o Na is the conjugate acid of NaOH NaOH is a strong base o so Na is neutral Cl is the conjugate base of HCl o HCl is a strong acid so Cl is neutral o NaCl is neutral is conjugate acid of NH3 Ex NH4F o NH4 o NH3 is a weak base …