Rates of reaction

• Rate of reaction


  How quickly a reaction happens
• Rate


  The change in a quantity divided by time
• The quantity could be mass or volume of gas that's usually made
• The rate could be changing over the time you measure, but that's true for any measurement over time
• Experiment on rate of reaction

  1. Reacting hydrochloric acid and sodium thiosulfate in a conical flask

  2. Stopping timer when can no longer see cross on paper below flask

  3. Repeating at different temperatures
• Increasing temperature


  Decreases time taken for reaction
• Measuring volume of gas produced

  1. Using gas syringe that fills up when connected to reaction vessel

  2. Plotting graph with quantity on y-axis and time on x-axis
• Tangent on graph


  Used to find rate at any time
• Ways to increase rate of reaction

  • Increasing concentration of reactants in solution
  • Increasing pressure of gas reactants
  • Increasing surface area of solid reactants by crushing into powder
  • Increasing temperature
  • Adding a catalyst
• Catalyst


  Reduces activation energy, making particles more likely to collide successfully and react
• Reversible reaction


  Products can return to original reactants
• Reversible reaction


  • Haber process - hydrogen and nitrogen react to make ammonia, which can also break down back into separate gases
• Closed system


  No particles or energy going in or out
• Equilibrium


  Rates of forward and reverse reactions are the same, so no overall change in quantities
• Increasing pressure in a reversible reaction

  Favours the forward reaction
• Increasing temperature in a reversible reaction


  Favours the endothermic (reverse) reaction
• In any reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic, and vice versa