Chemical Equilibrium

Transcription

1 Chemical Equilibrium Ch 17 Apr 28 7:40 AM A Reversible reaction is a chemical reaction that can occur in both the forward and the reverse directions N 2 (g) + 3 H 2 (g) 2NH3(g) Apr 16 1:21 PM 1

2 Equilibrium : two opposing processes occurring at the same rate (forward reaction and reverse reaction) A system at equilibrium is in balance H2O(l) H2O(g) It's a dynamic state; no net change Apr 16 1:17 PM Equilibrium constant (K eq ) Numerical value of the ratio of product to reactant concentrations It is constant only at a specific temperature. Apr 17 9:55 AM 2

3 Equilibrium constant expression The ratio of molar concentrations (Molarity) of products to reactants; each raised to a power equal to the coefficient in a balanced equation aa+bb < > cc + dd Brackets mean concentration expressed in molarity N 2 (g) + 3 H 2 (g) 2NH3(g) In equilibrium problems, we ignore (s) and (l). Why? Apr 16 1:26 PM Balance each equation. Write an equilibrium constant expression for: 1. N2(g) + 3H2(g) 2NH3(g) 2. 2N2O(g) 2N2 + O2(g) 3. 2O2(g) + CH4(g) CO2(g) + 2H2O(l) 4. 3CO2(g) + 4NCl3(g) 3CCl4(g) +2NO2 (g) +2NO (g) 5. O2(g) + 2H2(g) 2H2O (g) 6. 2H2S(g) 2H 2 (g) + S2(g) 7. 2CH4O(g) + 3O2(g) 2CO 2 (g) +4H2O(g) 8. 4NH3(g) + 5O2(g) 4NO (g) +6H2O(g) Apr 17 1:17 PM 3

4 N 2 (g) + 3 H 2 (g) 2NH3(g) In a closed 4.00L container at 289K, 4.6 moles of nitrogen, 6.8 moles of hydrogen and 10.0 moles of ammonia are present at equilibrium. Find the Keq for this reaction. Apr 28 8:55 AM 2CO(g) + O 2 (g) < > 2CO 2 (g) In a 1.0 liter container at equilibrium, 5.0 moles of carbon dioxide are found with 2.0 moles CO and 3.0 moles of O 2. Calculate the K eq. Apr 28 9:11 AM 4

5 Value of equilibrium constant (K eq ) shows the extent to which reactants are converted into products. K eq > 1: Products are favored at equilibrium K eq < 1: Reactants are favored at equilibrium Apr 17 9:56 AM In a closed 6.00L flask at 415K, 4.5 moles of H 2 O, moles of O 2, and moles of H 2 are found. what is the K eq for this reaction at this temperature. Are the products or reactants favored at this temperature? Explain. Apr 28 7:53 AM 5

6 Le Chatelier's principle: If stress is added to a system, the reaction flows in the direction to relieve the stress Three types of stresses Concentration changes Temperature changes Pressure changes Apr 30 10:22 AM Water and heat is formed when hydrogen gas reacts with oxygen at room temperature. 1. What is the molarity of O 2 if Keq = 14.3 and the equilibrium concentration of H 2 is M =0.088, and the H 2O is M = at 298K? 2. Which reaction (forward or reverse) is favored? 3. How do you know? 4. If this reaction had heat added to it, would the reactants or products be favored? 5. Write the equilibrium constant expression for the reaction of sodium sulfate with potassium hydroxide. Apr 17 1:17 PM 6

7 May 4 8:30 AM H 2 O + H 2 O H 3 O + + OH Hydronium ions Hydroxide ion Acid and Bases are measured on a ph scale which comes from the concentration of hydrogen or hydronium ions present in the solution. H + (Hydrogen) Is the same thing as H 3 O + (Hydronium) May 1 8:35 AM 7

8 Strong acids/bases: Ionizes completely in water (good conductor) Strong Acids: HCl, HNO 3, H 2 SO 4, HBr, HI, HClO 4 Strong Bases: NaOH, KOH, Ca(OH) 2,Ba(OH) 2 Weak acids/bases: Does not ionize completely in water (poor conductor) Weak Acids: HF, CH 3 COOH, H 3 PO 4, H 2 CO 3, HCN Weak Base: NH 3 May 1 8:35 AM Properties of : Acids Electrolytes Taste sour Turn litmus paper red React with metal to form H 2 Examples of items containing acids: Vinegar, Milk, Soda, Apples, citrus fruit Bases "Alkaline" Electrolytes Taste bitter Turn litmus paper blue Feel Slippery Examples of items containing bases: Ammonia, Lye, Drain cleaner, Baking Soda May 1 8:14 AM 8

9 3 Models of Arrhenius Acids produce hydronium ions bases produce hydroxide ions Brønsted Lowry Acids are Hydrogen ion Donors Bases are Hydrogen ion Acceptors May 1 8:14 AM Arrhenius Model: Acids dissociate in water Acids produce hydronium ions HCl + H 2 O H 3 O + + Cl or HCl H + + Cl Bases produce hydroxide ions LiOH Li + + OH May 1 8:16 AM 9

10 Brønsted Lowry Model Acids are Hydrogen ion Donors Bases are Hydrogen ion Acceptors HCl + H 2 O Cl Acid Base + H 3 O + Conjugate Base Conjugate Acid May 1 8:16 AM Directions: Label the Bronstead Lowry acids and bases, conjugate acids, and conjugate bases in the following reactions. Show the direction of hydrogen ion transfer 2. H 2 SO 4 + OH HSO 4 + H 2 O 3. HSO 4 + H 2 O SO H 3 O + 4. OH + H 3 O + H 2 O + H 2 O 5. NH 3 + H 2 O NH OH May 1 8:22 AM 10

11 H 2 O + H 2 O H 3 O + + OH Hydronium ions Hydroxide ion In water, the concentration of the hydronium ion is equal to the concentration of the hydroxide ion. These brackets mean concentration [H 3 O + ] = 1.0x10 7 M [OH ] = 1.0x10 7 M ([OH ] = [H 3 O + ]) = Neutral! May 1 8:37 AM There is an easier way to measure acidity/alkalinity ph Scale May 1 8:56 AM 11

12 ph is the measure of the hydronium concentration in a solution In pure water it is equal to 1 x By taking the negative log of this number we would say the ph of water is 7 In any solution the ph= log[h + ] May 6 8:23 AM ph = log[h + ] poh = log[oh ] ph + poh = 14 What is the ph of 1 x 10 5 M HCl? remember what we know about strong acids and bases ph = log(1x10 5 ) ph = 5 Meaning poh = 9 May 1 8:57 AM 12

13 ph = log[h + ] poh = log[oh ] What is the ph of ph + poh = M HNO 3? Remember what we know about strong acids and bases! May 1 8:59 AM What is the ph of 1 x 10 3 M NaOH? ph = log[h + ] poh = log[oh ] ph + poh = 14 May 1 9:00 AM 13