Day 7 Chemical Equilibrium Lecture Presentation Unit 7 Day 7 Chemical Equilibrium James F. Kirby Quinnipiac University Hamden, CT Edited by M. Day

TAKE OUT: Lab Notebook and Lab Handout Warm Up TAKE OUT: Lab Notebook and Lab Handout OPEN TO: Part E WATCH DEMO: Record Results

Lab Report: Procedure, Data, Discussion of Theory E Lab Report: Procedure, Data, Discussion of Theory E. Mg(OH)2 (s) ⇌ Mg2+(aq) + 2OH-(aq) H+(aq) + OH-(aq)  H2O (l) Procedure Observations Explanation Initial color of milk of magnesia and universal indicator Add 1 drop of 3 M HCl with constant stirring Additional drops of 3 M HCl Additional drops of HCl and NaOH

Agenda Help with Explanation Turn in Lab Copy Unit 7 Quiz Study Guide Work Time

Lab Report: Procedure, Data, Discussion of Theory C Lab Report: Procedure, Data, Discussion of Theory C. [Co(H2O)6]2+(aq) + 4HCl (aq) + Heat ⇌ [CoCl4]2-(aq) + 6H2O(l) Ag+(aq) + Cl-(aq)  AgCl(s) Add Cobalt Complex Ion Color Information Somewhere on Procedure Procedure Observations Explanation Add 6.0 M HCl drops (tube A) Add 0.1 M AgNO3 drops (tube B) Add distilled water drops (tube C) Add 5-6 grains CaCl2 to tube C Test tube C placed in ice water bath for 2-3 minutes Test tube C placed in hot bath for 2-3 mins

Lab Report: Procedure, Data, Discussion of Theory D Lab Report: Procedure, Data, Discussion of Theory D. 2CO2 (g) + H2O (l) ⇌ CO2 (aq) + H+(aq) + HCO3-(aq) Procedure Observations Explanation Initial color of solution Pull back on syringe to decrease pressure Push syringe to increase pressure

Clean Up for the Next Group!

Applications of LeChatelier’s Principle COMPLETE: All 4 lab stations WRITE: Observations (Explanation is homework) TIME: 10-12 minutes per station WHEN DONE: CLEAN UP FOR NEXT GROUP

Lab Report: Procedure, Data, Discussion of Theory A Lab Report: Procedure, Data, Discussion of Theory A. HIn (aq) ⇌ H+ (aq) + ln-(aq) H+(aq) + OH-(aq)  H2O(l) Procedure Observations Explanation Initial color of water and bromothymol blue Solution is green The green color shows that the pH of distilled water is between 6 and 7.6, and the indicator is a mix of Hln and I- Add 0.1 M HCl Solution turned yellow pH < 6.0 Add 0.1 M NaOH Solution turned green and finally ended on blue, pH > 7.6 Additional drops of HCl and NaOH Solution changes from yellow (with HCl) to blue (with NaOH)

Lab Report: Procedure, Data, Discussion of Theory C Lab Report: Procedure, Data, Discussion of Theory C. [Co(H2O)6]2+(aq) + 4HCl (aq) + Heat ⇌ [CoCl4]2-(aq) + 6H2O(l) Ag+(aq) + Cl-(aq)  AgCl(s) Procedure Observations Explanation Add 6.0 M HCl drops (tube A) Solution turned blue Add 0.1 M AgNO3 drops (tube B) White solid precipitate and solution turned pink Add distilled water drops (tube C) Solution turned pink Add 5-6 grains CaCl2 to tube C Crystals dissolved and solution turned blue Test tube C placed in ice water bath for 2-3 minutes Test tube C placed in hot bath for 2-3 mins

Lab Report: Procedure, Data, Discussion of Theory D Lab Report: Procedure, Data, Discussion of Theory D. 2CO2 (g) + H2O (l) ⇌ CO2 (aq) + H+(aq) + HCO3-(aq) Procedure Observations Explanation Initial color of solution Green color = pH 4.4 Pull back on syringe to decrease pressure Solution turned teal, pH = 4.8 Push syringe to increase pressure Solution turned green, pH = 4.4

Lab Report: Procedure, Data, Discussion of Theory E Lab Report: Procedure, Data, Discussion of Theory E. Mg(OH)2 (s) ⇌ Mg2+(aq) + 2OH-(aq) H+(aq) + OH-(aq)  H2O (l) Procedure Observations Explanation Initial color of milk of magnesia and universal indicator Purple solution with white solid suspended in liquid White solid is undissolved Mg(OH)2. Purple color is from the universal indicator and shows that some of the OH- ions are present b/c purple = pH > 10 Add 1 drop of 3 M HCl with constant stirring Solution immediately turned pink with more stirring pink color turned orange, green, then blue Additional drops of 3 M HCl Solution immediately turned pink; slower change to the blue-green end color Additional drops of HCl and NaOH Solution immediately turned pink; color remained pink and solution not cloudy

Change in Reactant or Product Concentration If the system is in equilibrium adding a reaction component will result in some of it being used up. removing a reaction component will result in some if it being produced.

Change in Volume or Pressure When gases are involved in an equilibrium, a change in pressure or volume will affect equilibrium: Higher volume or lower pressure favors the side of the equation with more moles (and vice-versa).

Change in Temperature Is the reaction endothermic or exothermic as written? That matters! Endothermic: Heats acts like a reactant; adding heat drives a reaction toward products. Exothermic: Heat acts like a product; adding heat drives a reaction toward reactants.

An Endothermic Equilibrium

An Exothermic Equilibrium The Haber Process for producing ammonia from the elements is exothermic. One would think that cooling down the reactants would result in more product. However, the activation energy for this reaction is high! This is the one instance where a system in equilibrium can be affected by a catalyst!

Catalysts Catalysts increase the rate of both the forward and reverse reactions. Equilibrium is achieved faster, but the equilibrium composition remains unaltered. Activation energy is lowered, allowing equilibrium to be established at lower temperatures.