SCH4U Unit #2: EQUILIBRIUM

1. SCH4UUnit #2: EQUILIBRIUM Ms. Cornacchione Wed Mar 5th 2014

2. Unit #2: EquilibriumTOPICS • Equilibrium (EQM) Introduction • EQM Law & EQM Constant (Kc) • Qualitative Changes (Le Chatelier’s Principle) • Quantitative Changes & RXN Quotient (Q) • Solubility Equilibria • Learn To Calc: • Write an Expression for KC • Calculate KC • Find an R or P EQM concentration given KC

3. Equilibrium Law & Equilibrium Constant • The Equilibrium Law mathematically describes a chemical system at equilibrium [ ] C • Equilibrium Constant(KC)defines the equilibrium law for a given system. K is a constant for a reaction at a specific temperature. IT IS UNITLESS!!  [ ] concentrations at equilibrium A, B, C, D are reactants and products in (g) or (aq) state ONLY a, b, c, d are the coefficients in the balanced chemical equation

4. Equilibrium Constant EXAMPLES [CO2]3[H2O]4 [C3H8] [O2 ]5 Write expressions for Kc for each of the following reactions: • C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) • Ca(s) + 2H2O(ℓ)  Ca(OH)2(aq) + H2(g) • AgNO3(aq) + NaCℓ(s) AgCℓ(s)+ NaNO3(aq) D. Na2CO3(s) + 2HCℓ (aq) 2NaCℓ(aq) + H2O(ℓ) + CO2(g) Kc = [Ca(OH)2][H2] Kc = [NaNO3] [AgNO3] Kc = [NaCl]2[CO2] [HCl]2 Kc =

5. Equilibrium Law & Equilibrium Constant The value of K is a constant for a given reaction at a certain Temperature, regardless of initial concentration

6. Equilibrium Law & Equilibrium Constant The value of KC is a constant for a given reaction at a certain Temperature, regardless of initial concentration

7. KC & EQM Position The equilibrium constant, K, will tell you if the equilibrium position is far to the left (reactants) or far to the right (products)

8. Calculate KC – EXAMPLE 1

9. Calculate KC – EXAMPLE 2

10. Heterogeneous vs. Homogeneous EQM Homogeneous – all R & P in the same state of matter Heterogeneous – R & P present in at least two different states If pure solids (s) or liquids (l) are involved in an EQM system, their concentrations are NOT included in the equilibrium law equation

11. Heterogeneous vs. Homogeneous EQM Write the Equilibrium Law equation for the following reaction: Why not include (s)?

12. Calculating EQM Concentration Example Methane gas reacts with water vapour to produce carbon monoxide gas and hydrogen gas according to this equation: CH4(g) + H2O(g) ↔ CO(g) + 3H2(g) At equilibrium: [CO] = 0.300 M, [H2] = 0.800 M, [CH4] = 0.400 M. If K is 5.67, calculate the concentration of water vapour

13. Equilibrium Law and Equilibrium Constant

14. EQM Constant - Practice Makes Perfect • Study Sample Problems (Pg 430 & 434) • Do Practice Problems (Page 436) and check your answers! • “EQM Law & EQM Constant” Worksheet

15. Unit #2: EquilibriumTOPICS • Equilibrium (EQM) Introduction • EQM Law & EQM Constant (Kc) • Qualitative Changes (Le Chatelier’s Principle) • Quantitative Changes & RXN Quotient (Q) • Solubility Equilibria

16. Qualitative Changes in EQM • Chemical systems at EQM may be disturbed by changes in concentration [ ], temperature (T), pressure (P) • The EQM position shifts to oppose these changes EQM Established Rxn Starts Δ in P, T, [ ] New EQM EQM Shift (Change the EQM Position)

17. Le Châtelier’s Principle - DEMO

18. RECAP: Equilibrium Position • Equilibrium position is the relative concentrations of reactants and products in a system in dynamic equilibrium

19. Products Concentration Reactants time RECAP: Equilibrium Position + + C D A B Reactants Reactants Concentration Products Concentration Products time time EQM Position: CENTRE EQM Position: RIGHT EQM Position: LEFT

20. Le Châtelier’s Principle: When a dynamic equilibrium system is disturbed by a change in conditions, the position of the equilibrium moves to oppose the change • Le Châtelier’s Principle allows prediction of qualitative changes in conditions on EQM systems • It is a guideline/tip but not an explanation • We will use Collision Theory to Explain

22. Le Châtelier’s Principle – Δ CONCENTRATION • Add Reactant – Shift to Products (RIGHT) Explain: Increases # of successful collisions of forward reaction A B *Temporary. Why?

23. Le Châtelier’s Principle – Δ CONCENTRATION • Add Product – Shift to Reactants (LEFT) Explain: Increases # of successful collisions of the reverse reaction A B

24. Le Châtelier’s Principle – Δ CONCENTRATION • RemoveProduct – Shift to Products (RIGHT) Explain: Decreases # of successful collisions of reverse reaction A B

25. Le Châtelier’s Principle – Chemical Engineering Example • HNO3(aq) is used in the synthesis of fertilizer, explosives, dyes and perfumes.NO (g) is not as useful. • If we let the reaction proceed in a closed vessel, an equilibrium will be established Is it possible to improve the yield further than this, by changing conditions to favor the production of products?

26. Le Châtelier’s Principle – ΔENERGY Think of energy as a reactant or product: • If the Reaction is Endothermic: Temp (°C) Temp (°C) If you increase the Temp of the reaction, then the reaction solution will turn reddish brown

27. Le Châtelier’s Principle – Δ ENERGY Think of energy as a reactant or product: • If the Reaction is Exothermic: Temp (°C) Temp (°C) If you decreasethe Temp of the reaction, then the reaction shifts to the right

28. Le Châtelier’s Principle – Δ GAS VOLUME (PRESSURE) RECALL (Gr 11) - Decreasing the volume of a container of ideal gases increases the pressure and vice versa (Boyle’s law). The total pressure is the sum of all partial pressures. • IncreasingPressure – Shifts towards FEWERmoles (g) • DecreasingPressure – Shifts towards MOREmoles (g) Explain (if > mol (g) on reactant side): If we reduce the volume of the container, the partial pressures of all reactants may be larger than those of all products, so the change in concentration of reactants may be greater than the chance in concentration of the products… […refer to change in reactant concentration trends.]

29. Le Châtelier – ΔGAS VOLUME (PRESSURE) • IncreasingPressure – Shifts towards FEWERmoles (g) • DecreasingPressure – Shifts towards MOREmoles (g) P At EQM V  EQM Shift to NH3(g)

30. FACTORS That DO NOT Change EQM Position • Catalysts • Inert Gases • State of Reactants

31. Factors That Don’t Affect EQM – Catalyst Ea Ea E react E prod Potential Energy Potential Energy E prod E react • A CATALYST lowers the ACTIVATION ENERGY of the reaction by providing a different reaction pathway. • Activation Energy is lowered for BOTH FORWARD AND REVERSE REACTIONS. • BOTH rates are therefore increased by the same amount and so the EQUILIBRIUM DOES NOT SHIFT!!!!

32. Factors That Don’t Affect EQM – Inert Gas • Inert gases (eg. He(g)) do not react • Although total pressure increases, the partial pressures of the reactants and products remain the same • Although there are more collisions, collisions with inert gases will NOT result in a reaction. The number and frequency of collisions between reactant and products remainthe same NO EQUILIBRIUM SHIFT!!!!

33. Factors That Don’t Affect EQM – State of Reactant • Equilibrium is affected only by changes in concentration of entities that are in the same state of matter as the substances involved in the chemical reaction system • Solid iodine sublimes (becomes gas) before reacting • At EQM, the reaction vessel will have hydrogen gas, iodine gas, and hydrogen iodide gas • There is a phase EQM between solid and gaseous iodine • Adding more SOLID iodine will not affect this EQM

34. N2(g) + 3H2(g) 2NH3(g) (H < 0) Kc = Optimizing the Haber Bosch Process • Favourable conditions: • High • High • LOW • LOW [N2] & [H2] Pressure Temperature [NH3] In practice a compromise temperature is used. Too low will slow the reaction down.

35. Summary of EQM Changes Shift Change

36. Qualitative Changes in EQM Systems

37. Qualitative Changes (Le Châtelier’s Principle) – Practice Makes Perfect! • Read Section 7.4 • Do Practice Problems #1-4 (Page 446) and check your answers! • “Le Châtelier’s Principle” Worksheet