1.7

• What is a reversible reaction?

  A reaction that can go in either direction
• What is established in a closed system during a reversible reaction?

  A dynamic equilibrium
• What happens to the concentrations of reactants and products in a dynamic equilibrium?

  They remain constant over time
• What is the term for the proportion of products to reactants in an equilibrium mixture?

  Position of equilibrium
• What occurs if a system at equilibrium is subjected to a change?

  The position of equilibrium shifts to minimize the change
• What factors influence the position of equilibrium?

  Concentration, pressure, and temperature
• What effect does a catalyst have on reaching equilibrium?

  It decreases the time to reach equilibrium
• According to Le Chatelier’s principle, what happens if the concentration of a reactant is increased?

  The position of equilibrium moves to the right
• What happens when hydrochloric acid is added to the equilibrium of the reaction 2CrO42–(aq) + 2H+(aq) ⇌ Cr2O72–(aq) + H2O(l)?

  The equilibrium shifts to the right
• What is the effect of adding sodium hydroxide to the equilibrium of the same reaction?

  The equilibrium shifts to the left
• How does increasing pressure affect the position of equilibrium in gas reactions?

  It moves to the side with fewer gas molecules
• In the reaction 2NO2(g) ⇌ N2O4(g), what happens if pressure is increased?

  The equilibrium shifts to the right
• What direction does the position of equilibrium move when temperature is increased in an exothermic reaction?

  It moves to the left
• What is Kc in terms of equilibrium?

  The equilibrium constant in terms of concentration
• How is Kc expressed for a general equilibrium reaction aA + bB ⇌ cC + dD?

  Kc = [C]^c [D]^d / [A]^a [B]^b
• What should be used around formulae for Kc calculations?

  Square brackets
• Are solids included in the expression for Kc?

  No, solids are never included
• What affects the value of Kc?

  Only temperature affects Kc
• What is the unit of Kc for the reaction 2NO2(g) ⇌ N2O4(g)?

  dm³ mol⁻¹
• What is an acid defined as?

  A proton (H+) donor
• How is a strong acid characterized in solution?

  It is fully dissociated in aqueous solution
• What is an example of a strong acid?

  HCl(aq)
• How is a weak acid characterized in solution?

  It is only partially dissociated in aqueous solution
• What is the difference between concentrated and dilute acids?

  Concentrated has less water than acid
• What does the pH scale measure?

  The concentration of aqueous hydrogen ions
• How is pH calculated from hydrogen ion concentration?

  pH = –log[H+]
• What is the pH of a solution with a H+(aq) concentration of $3.9 \times 10^{-6} \text{ mol dm}^{-3}$?


  pH = 5.4
• How is the hydrogen ion concentration calculated from pH?

  [H+] = 10^(-pH)
• What is the hydrogen ion concentration of a sample with a pH of 2.2?

  [H+] = 6.3 × 10⁻³ mol dm⁻³
• What is a standard solution and how is it prepared?

  • A solution with accurately known concentration
  • Prepared from a solid:

  1. Calculate mass of solid required
  2. Weigh solid into a weighing bottle
  3. Transfer solid to a beaker and wash out
  4. Add water and stir until dissolved
  5. Pour into a volumetric flask and wash out
  6. Add water to just below graduation mark
  7. Add water dropwise to reach mark
  8. Invert flask to mix thoroughly
• What are the steps in performing an acid-base titration?

  1. Pour acid into burette and fill jet
  2. Use pipette to add base to conical flask
  3. Add indicator to the flask
  4. Run acid into flask, swirling
  5. Stop when indicator changes color
  6. Read final burette volume and calculate titre
  7. Repeat until two readings are within 0.20 cm³
  8. Calculate mean titre
• What does a pipette measure?

  A set volume of solution
• What does a burette measure?

  Differing volumes of solution
• How does a burette allow for precise addition of a solution?

  It lets you add solution drop by drop