1 / 12

Chapter 18: Chemical Equilibria

Au 2 O 3 (s) + 2 Fe (s) 2 Au (s) + Fe 2 O 3 (s). Ex:. Chapter 18: Chemical Equilibria. Irreversible reactions: The reactants combine to form products and the reaction stops when the limiting reagent has been completely used up. “Only” the forward reaction occurs.

guy-emerson
Télécharger la présentation

Chapter 18: Chemical Equilibria

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Au2O3 (s) + 2 Fe (s) 2 Au (s) + Fe2O3 (s) Ex: Chapter 18: Chemical Equilibria Irreversible reactions: The reactants combine to form products and the reaction stops when the limiting reagent has been completely used up. “Only” the forward reaction occurs. Reversible reactions: Both the forward and the reverse reaction occur to a significant degree. Forward: 3 H2(g) + N2(g) 2 NH3(g) 3 H2(g) + N2(g) 2 NH3(g) Reverse: 3 H2(g) + N2(g)⇋2 NH3(g) anim Equilibrium: A reaction is at equilibrium when Rate forward rxn = Rate reverse rxn

  2. General form of equilibrium constant, Keq: aA + bB ⇋cC + dD If K > 1, then more products than reactants present at equilibrium If K < 1, then more reactants than products present at equilibrium

  3. [NH3] Keq = [N2] [H2] Concentration Time ⇋ N2(g) + 3 H2(g) 2 NH3(g) 2 H2 3 N2 NH3

  4. Heterogeneous equilibria • Occurs when the reactants and products are in more than one state • Because the molar concentration of solids and liquids do not change, SOLIDS AND LIQUIDS NEVER appear in equilibrium constant calculations (they have a concentration value of 1). Ex: BaCl2 (s)⇋ Ba2+(aq) + 2 Cl-(aq) Ksp • Since this particular type of equilibrium involves the solubility of the product, it is given a special designation: • Ksp = solubility product constant

  5. [CO][H2] Keq = [H2O] [CO2] Keq = [CO] Heterogeneous equilibria (cont.) Ex: H2O (l)⇋ H2O (g) • What are the equilibrium constants for the following: • C10H8(s)⇋ C10H8(g) • CaCO3(s)⇋ CaO (s) + CO2(g) • C (s) + H2O (g)⇋ CO (g) + H2(g) • FeO (s) + CO (g)⇋ Fe (s) + CO2(g) Keq = [C10H8] Keq = [CO2]

  6. The equilibrium constant for the reaction below at 700K is 0.44. What is the concentration of the carbon dioxide if [H2O] = 0.16 M, [CO] = 0.15 M and [H2] = 0.14 M? H2O(g) + CO(g) ⇋ H2(g) + CO2(g) 1. Set up the equilibrium expression 2. Substitute in the known values and solve for the unknown. [CO2] = 0.075 M

  7. Molar solubility: the number of moles of the solute per liter in a saturated solution Ex 1: What is the molar solubility of lead(II) iodide if its Ksp is 8.7 x 10–9 ? PbI2(s)  Pb2+ + 2 I– x = the molar solubility x 2x Ksp = [Pb2+][I–]2 8.7 x 10–9 = [x][2x]2 8.7 x 10–9 = 4x3 x = 1.3 x 10–3 M Ex 2: What is the molar solubility of PbI2 if 0.2 M KI is added? [I–] = 0.2 M 8.7 x 10–9 = [x][0.2]2 x = 2.2 x 10–7 M

  8. Ex 3: What is the Ksp of Pb3(PO4)2 if it has a molar solubility of 1.5 x 10-9 M? 1) Write out reaction equation: Pb3(PO4)2 3 Pb2+ + 2 PO43- 2x 3x 2) Write out Ksp expression: Ksp = [Pb2+]3 [PO43-]2 Ksp = (3x)3 (2x)2 Ksp = (27x3)(4x2) Ksp = 108x5 x = 1.5 x 10-9 Ksp = (108)(1.5 x 10-9 )5 Ksp = 8.2 x 10-43

  9. Le Chatelier’s Principle: When a stress is applied to an equilibrium, the equilibrium will shift to alleviate the stress. Fe+3(aq) + SCN-1(aq) ⇋ FeSCN+2(aq) Colorless ⇋ Dark red Reactants Products Left shift = more reactants (color is lighter) Right shift = more products (color is darker) Initial color

  10. Other ways to cause a Le Châtelier Shift: 3 H2(g) + N2(g) + heat ⇋ 2 NH3(g) What kind of shift would you see if: *Pressure increased? Right shift  [NH3] increased?  Left shift Right shift  Heating temperature increased? *A gas–phase equilibrium will shift to the side of the reaction that takes up less space (smaller coefficient sum) when pressure is increased.

  11. CH4(g) + 2 Cl2(g)⇋ CCl4(g) + 2 H2(g) + heat What kind of shift would you see if: Pressure increased? No Change Heating temperature increased?  Left shift

  12. 2 drops 0.05 M NaSCN 2 drops 0.01 M Fe(NO3)3 3 drops H2O 1 2 3 4 + 2 drops H2O + 1 drop 1 M NaNO3 H2O 0.01 M Fe(NO3)3 0.1 M Fe(NO3)3 0.05 M NaSCN 1 M NaNO3 + 2 drops 0.1 M Fe(NO3)3 + 2 drops 0.05 M NaSCN

More Related