CHEM 1442 1st Edition Lecture 11Outline of Last Lecture I. Le Chatelier’s principleII. pHOutline of Current Lecture III. Ch. 18Current LectureChapter 18Example: Determine ∆H for the reaction below:2 NO2(g) ⇌ N2(g) + 2 O2(g) ∆H = ?Use the following data.1/2 N2(g) + ½ O2(g) ⇌ NO(g) ∆H = +90.29 kJ/mol2 NO2(g) ⇌ 2 NO(g) + O2(g) ∆H = +114.18 kJ/molAnswer:2 NO2(g) ⇌ N2(g) + 2 O2(g) ∆H = -66.40 kJ/molHess’s Law: the enthalpy of the overall reaction = the sum of enthalpies of individual reactionsK of an overall reaction = the product of Ks of the individual reactionsExample: identify an acid and a base in the following reactionHPO42- (aq) + HSO-4 (aq)  H2PO4-(aq) + SO42-(aq)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Answer:H2PO4- accepted H+ (base)SO42- donated H+ (acid)Example: Classify the following acids as strong or weakAnswer:HNO3 – strong acidHNO2 – weak acidHC2H3O2 – weak acidHClO4 – strong acidHF(aq) – weak acidHCl(aq) – strong acidHCN(aq) – weak acidH2S(aq) – weak acidStrong acids:HCl, HBr, HI, HNO3, HClO4, H2SO4, HClO3Quantitative Approach to Compare Acid StrengthExample: Write an acid-dissociation reaction for HCN?HCN(aq) + H2O(l)  CN-(aq) + H3O+(aq)Write the equilibrium constant expression for this reaction.K = [CN-] [H3O+]/ [HCN] = 6.2 x 10-10Equilibrium constant for an acid dissociation reaction is called:Ka – acid-dissociation constant (or acid ionization constant or acidity constant)Ka: can be used to compare “acid strength,” which is the “ability (tendency) to lose a proton (H+)”The bigger the Ka value, the stronger the acidp-ScaleIn the p-scale, as X increases, pX decreases.Small K (< 0.01) Reactants dominate the equilibrium compositionIntermediate K (0.01-100) Neither reactants nor products will dominateLarge K (>100) Products dominate the equilibrium compositionAmines“Organic” Weak BasesThe functional group: amino groupConjugate Acid-Base Pairs- Loss of a proton from an acid forms its conjugate base- Gain of a proton by a base forms its conjugate acid- A conjugate base of a weak acid is a weak base- A conjugate base of a weaker acid is a stronger base- A conjugate base of a stronger acid is a weaker base- A conjugate acid of a weaker base is a stronger acid- A conjugate acid of a stronger base is a weaker