Notes handout, equilibrium video part 2

2 Le Chatelier’s Principle: if you disturb an equilibrium, it will shift to undo the disturbance. Remember, in a system at equilibrium, K eq is a constant. 3 Common ways to disturb an equilibrium: Le Châtelier’s Principle

3 Effect of Temperature Changes The equilibrium constant is temperature dependent. For an endothermic reaction, heat can be considered as a reactant. For an exothermic reaction, heat can be considered as a product. Adding heat causes the reaction to shift to get rid of this extra heat

4 Effect of Temp. Change N 2 + O 2 2NO ΔH rxn = kJ What is effect of increasing T?

5 Effect of Change in Concentration For reaction Butane Isobutane K c at 25 o C = 2.50 What would be the effect of adding 1.5 M butane?

Common Ion Effect At equilibrium the conc. of butane is 0.2M and Isobutane is 0.5M. If 2.00 mol / L isobutane is added, what will the new equilibrium concentrations be? 6

7 Effect of Volume Change in Gas Phase Equilibrium In reactions involving gases, if you change the size of the container, you will also change the gas concentration. The effect of a volume decrease would be to shift the equilibrium to the side with the fewer numbers of gas molecules

8 In the reaction: 2NO 2 N 2 O 4 K c = 170 at 298K What would be the effect of halving the volume of the container?

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10 Solubility Equilibria The solubilities of slightly soluble compounds can be written as equilibrium expressions. Write the equilibrium expression for the dissolving of silver bromide: Since the reactant is solid, only the products (ions) are involved in the K sp expression K sp (solubility product constant):

11 K sp Values K sp values can be found on charts of K sp constants at a given temperature Relative solubilities of compounds can be compared IF the ion ratios in the two compounds are the same, but not if they’re different. Compare solubilities of: AgCl and AgI Compare solubilities of: Ca(OH) 2 and CaSO 4

12 K sp Values

13 Solubility Product Calculations Write the equilibrium expression for the dissolving of calcium fluoride: If the solubility of CaF 2 is 2.4 x mol/L at 25°C, find the K sp

14 Solubility Product Calculations The K sp for barium sulfate is 1.1 x Find the solubility in mol/L and g/L.

15 The K sp for magnesium fluoride is 5.2 x Find the solubility in mol/L.

16 Common Ion Effect: when an ion common to the equilibrium is added, it affects the equilibrium balance. If you add AgCl to 1.0L of 0.55M NaCl, what mass of AgCl will dissolve? The K sp of AgCl = 1.8 x

17 The Ksp for AgCl is 1.8 x If the concentration of silver ions is 1.2 x 10 -5, is the solution saturated, or will more dissolve?

18 The concentration of magnesium ions in solution is 1.5 x If NaOH is added to make the hydroxide concentration 1.0 x 10 -4, will Mg(OH) 2 precipitate form? The K sp for Mg(OH) 2 is 5.6 x

19 A solution of mL of M AgNO 3 is prepared. Will AgCl precipitate if 5.0 mL of 0.025M HCl are added?