2Standard 9b: equilibrium conditions Reversible ReactionsMost reactions are ‘reversible’Forward reaction: reactants make productse.x. 3O2(g) 2O3(g)Reverse reaction: products make reactantse.x. 2O3(g) 3O2(g)In a reversible reaction the forward and reverse reactions occur at the same timee.x. 3O2(g) 2 O3(g)
4Reversible reactions reach equilibrium: a balance between reactants and productsConditions of Equilibrium:rate of forward reaction = rate of reverse reactionConcentration of reactants and products is constant (does not change)NOTE:Rate = speedConcentration = number of particles or molesexample: [HCl] = concentration of HCl6M HCl = 6mole/L HCl= 6 moles of HCl per liter of solution
6Reversible reaction: X Y concentrationrate[Y]Y XtimetimeConcentrations are constantReaction rates are equalequilibrium
7Summary 3Describe the part of each graph that illustrates equilibrium conditions.
8Le Chatelier’s Principle 9a: Le Chatelier’s PrincipleLe Chatelier’s PrincipleA system in equilibrium will react to relieve stress (change) and re-establish equilibriumStress:Adding reactants or productsRemoving reactants or productsChanging temperatureChanging pressure (for gases only)
9Summary 4According to Le Chatelier’s Principle, what will happen to a system at equilibrium if more reactants or products are added?
10Example: N2(g) + 3H2(g) NH3(g) + heat Stress: Add N2Stress relief:Forward reaction (→) to get rid of N2H2 is used up (↓)NH3 and Heat are produced (↑)
11Summary 5: N2(g) + 3H2(g) NH3(g) + heat Stress: remove N2Stress relief:Which way does equilibrium shift?What happens to [H2]?What happens to [NH3]?What happens to heat?
12Stress relief. Adding products or reactants Equilibrium shifts to remove additionRemoving products or reactantsEquilibrium shifts to replace what has been removedGassesEquilibrium shifts to produce:more gas at low pressureLess gas at high pressure
13Summary 6Why would a gas equilibrium system produce more gas at low pressure and less gas at high pressure?
19Equilibrium Constant: Keq HONORS Standard 9c: equilibrium constantEquilibrium Constant: KeqAt equilibrium concentrations are constantKeq represents concentrations of reactants and products at equilibriumExample: aA + bB cC + dDKeq = [C]c[D]d[A]a[B]b
20Summary 9write Keq expression for the Haber-Bosch Process: N2(g) + 3H2(g) 2NH3(g)
21Concentrations calculated in mol/L (M) Only solutions(aq) & gases(g) are consideredNo solids (s)No liquids (l)Example: 2H2O(l) 2H2(g) + O2(g)Keq = [H2]2[O2]
23What Keq tells usIf Keq ≤ 1 There are more reactants than products at equilibriumIf Keq ≤ 1/100 There are mostly reactants at equilibriumIf Keq ≥ 1 There are more products than reactants at equilibriumIf Keq ≥ 100 There are mostly products at equilibrium
24Summary 11 CO(g) + 2H2(g) CH3OH(g) Keq=290 at 430°C Write the expression for KeqReaction is…(mostly products or reactants?)
25Solubility Ksp is the equilibrium constant for solubility Example: AgCl(s) Ag+(aq) + Cl-(aq)Ksp AgCl = 1.77 x 10-10Does not really dissolve, mostly solidExample: AgNO3(s) Ag+(aq) + NO3-(aq)Ksp AgNO3 ~ 1 x 1010Very soluble
26Summary 13Write the balanced equation for the dissolving of sodium sulfate.Write a Ksp expression for the reaction.