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Advanced Reaction Topics

Advanced Reaction Topics. Advanced Reaction Topics. Reaction Rates Equilibrium Acids and Bases Redox Chemistry. Reaction Rates. Reaction Rates. Things that affect the rate of a reaction Temperature Increasing the temperature 10 °C doubles the reaction rate typically Concentration

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Advanced Reaction Topics

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  1. Advanced Reaction Topics

  2. Advanced Reaction Topics • Reaction Rates • Equilibrium • Acids and Bases • Redox Chemistry

  3. Reaction Rates

  4. Reaction Rates • Things that affect the rate of a reaction • Temperature • Increasing the temperature 10°C doubles the reaction rate typically • Concentration • Surface Area • Catalyst • Every reaction is different and has a different reaction rate.

  5. Collision Theory • Reactions happen when molecules collide with each other • The reaction only happens IF: • They collide with enough energy • They collide with the right orientation.

  6. How Do They Relate? • Things that affect the rate of a reaction • Temperature • Increasing Temperature increases the energy in a collision. • Concentration • Increases the number of particles in the same volume and therefore the number of collisions • Surface Area • Increases the accessible area for collisions

  7. Equilibrium

  8. Fishbowl Demo • What are the characteristics once it reaches equilibrium? • The amount of “reactants” and “products” is not changing • “Reactions” are still occurring in both the forward and reverse direction. • The rate of the “reactions” is the same at equilibrium

  9. Characteristics of Equilibrium • The amounts of the reactants and products do not change while the system is at equilibrium. • Consider: N2 + 3H2⇌ 2NH3 Notice the double half arrows

  10. Characteristics of Equilibrium • The forward and reverse reactions still both occur but at the same rate. • For this reason, equilibrium can also be called dynamic equilibrium

  11. Acids and Bases

  12. Hydrochloric Acid • HCl(aq) • What type of compound is it? • What type of electrolyte is hydrochloric acid?

  13. Hydrochloric Acid • Why does it light up? • What must be present in solution? • Is hydrochloric acid an ionic compound? • No. It is in a small subset of covalent compounds.

  14. Hydrochloric Acid • It must be making some ions in solution • What are the ions? • HCl + H2O H3O+(aq) + Cl-(aq)

  15. Hydrochloric Acid • H3O+ is called the hydronium ion • Things that make hydronium ions in water are called acids.

  16. A Word About Hydronium • Depending on how you look at it acids make • H+ - hydrogen ion • H3O+ - hydronium ion • The two are interchangable • H+ + H2O  H3O+ • Anytime you see one it can mean the other.

  17. Hydrochloric acid (HCl) Muriatic acid Sulfuric acid (H2SO4) Battery acid Nitric acid (HNO3) Acetic acid (HC2H3O2) Vinegar Phosphoric acid (H3PO4) Citric Acid Lactic Acid Ascorbic Acid Vitamin C Acetylsalicylic Acid Aspirin Stearic Acid Common Acids

  18. Sodium hydroxide Lye, Caustic Soda Calcium hydroxide Lime Magnesium hydroxide Milk of magnesia Ammonia Sodium hypochlorite Bleach Sodium hydrogen carbonate Baking Soda Calcium carbonate Chalk Tums Common Bases

  19. Acids and Bases • Arrhenius Definitions • Arrhenius Acid – a substance that dissociates and produces hydronium ions in water • Arrhenius Base – a substance that dissociates and produces hydroxide ions in water • Brønsted-Lowry Definitions • Brønsted-Lowry Acid – a substance that donates a hydrogen ion (H+) (a proton) • Brønsted-Lowry Base – a substance that accepts a hydrogen ion (H+) (a proton)

  20. Acid and Base Definitions • There is quite a bit of overlap between the definitions • HCl + H2O  Cl- + H3O+ • HCl dissociates and produces hydronium ions • Arrhenius Acid • HCl donates an H+ to water • Brønsted-Lowry Acid • All Arrhenius Acids are Brønsted-Lowry Acids and vice versa.

  21. Acid and Base Definitions • Relations between the base definitions are not as simple. • NaOH dissolves in water to form Na+ and OH- • Arrhenius Base • NaOH + H+ Na+ + H2O • Brønsted-Lowry Base • Hydroxides are both Arrhenius and Brønsted-Lowry Bases. • Non-hydroxide bases can’t be Arrhenius bases • No hydroxide obviously… • Non-hydroxide bases will be Brønsted-Lowry bases • CO32- + H+  HCO3- • NH3 + H+ NH4+

  22. Acid and Base Definitions • Arrhenius acids and bases are tied to water • Brønsted-Lowry acids and bases are not. • Brønsted-Lowry can be used to describe reactions in the gas phase or in other solvents besides water.

  23. Acid-Base Definitions • Monoprotic acid – an acid that has one ionizable hydrogen • HCl, HNO3 • Diprotic acid – an acid that has two ionizable hydrogens • H2SO4 • Triprotic acid – an acid that has three ionizable hydrogens • H3PO4 • What kind of acid is acetic acid, HC2H3O2? • Monoprotic • Typically only hydrogens written first are ionizable.

  24. Autolysis of Water • Water spontaneously splits itself • 2H2O ⇌ H3O+ + OH– • An equilibrium system. • Makes equal parts hydronium and hydroxide • Equal parts acid and base • Water is neutral.

  25. Autolysis of Water • We will use brackets to represent molarity • [H3O+] is the molarity of the hydronium ion. • When acids and bases are dissolved in water [H3O+][OH–] = Kw = 1x10-14

  26. Acid Base Reactions • Acid Base Neutralization Reaction • HA + B  A + HB • Transfer of hydrogen ions (H+) • Hydrochloric acid and sodium hydroxide solutions are mixed

  27. Acid Base Reactions • Acid Base Neutralization Reaction • HA + B  A + HB • Transfer of hydrogen ions (H+) • Acetic acid and barium hydroxide solutions are mixed.

  28. Acid Base Reactions • Acid Base Neutralization Reaction • HA + B  A + HB • Transfer of hydrogen ions (H+) • Ammonia and sulfuric acid solutions are mixed

  29. Acid Base Reactions • Acid Base Neutralization Reaction • HA + B  A + HB • Transfer of hydrogen ions (H+) • Hydrochloric acid and sodium sulfide solutions are mixed.

  30. Acids • Hydrochloric acid • Is it an electrolyte? • Why is it an electrolyte? • Acetic acid • Is it an electrolyte? • Why is it an electrolyte? • Why doesn’t it light up as much as hydrochloric acid?

  31. Strength of Acids and Bases • Hydrochloric acid completely dissociates • HCl + H2O  H3O+ + Cl- • Acetic acid doesn’t make as many ions • Acetic acid partially dissociates • HC2H3O2 + H2O ⇌ H3O+ + C2H3O2– • Around 0.5% of acetic acid molecules make hydronium ions • Reactant side is very favored.

  32. Strength of Acids and Bases • Strong acid or base – an acid or base that completely reacts with water to form hydronium ions or hydroxide ions. • Strong acids – hydrochloric, sulfuric, nitric • Strong bases – LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 • Weak acid or base – an acid or base that partially reacts with water to form hydronium ions or hydroxide ions. • Weak acids – everything except the above • Weak bases – everything except the above

  33. Strong Acid Weak Acid

  34. Strength of Acids and Bases • Strength does not describe concentration • Consider • A bottle of “glacial” acetic acid (99%) • A bottle of concentrated sulfuric acid (98%) • Both have (nearly) the same concentration • Acetic acid will not ionize as much in water as sulfuric acid will • Acetic acid is a “weak” acid

  35. Concentration of Acids • If not all acids completely dissociate in water • The concentration of the acid molecules is different for every acid • The concentration of the hydronium ion in different acids is different • Need a system that describes the concentration of acids.

  36. pH • pH = -log [H3O+] • Also define a relationship for the amount of base • pOH = -log [OH–] • How do you reverse a log? • 10-pH = [H3O+] • 10-pOH = [OH–]

  37. How are pH and pOH related? Kw = [H3O+][OH–] log Kw = log ([H3O+][OH–]) log Kw = log [H3O+] + log [OH–] log 1x10-14 = log [H3O+] + log [OH–] -14 = log [H3O+] + log [OH–] 14 = -log [H3O+] + -log [OH–] 14 = pH + pOH

  38. pH Scale • Take 7 minutes to fill in this pH scale using the chemical formulas you know.

  39. Practice Problems • What is the pH of a solution with [H+] of 1.0x10-3 M?

  40. Practice Problems • What is the pOH of a solution with [H+] of 1.0x10-3 M?

  41. Practice Problems • What is the [OH-] of a solution with a pH of 9.00?

  42. Practice Problems • What is the [OH-] of a solution with an [H3O+] concentration of 1.0x10-5 M?

  43. Practice Problems • What is the pH of a solution with a hydronium ion concentration of 2.55x10-4M?

  44. Practice Problems • What is the pOH of a solution that has a hydronium ion concentration of 5.50x10-8 M?

  45. Indicators • Colored compounds that are sensitive to changes in pH • Indicators will change color based on how acidic or basic the conditions around it are • Chemical reaction with the acids or bases

  46. Universal Indicator • Universal Indicator is a mixture of different indicators. • Resulting color depends on each of the four indicator’s states

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