Rate Of Reactions

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Rate Of Reactions

  1. 1. Rate of Reactions
  2. 2. Fast or Slow Reactions <ul><li>Extremely slow reactions </li></ul><ul><ul><li>Iron rusting </li></ul></ul><ul><ul><li>Limestone weathering </li></ul></ul><ul><li>Extremely fast reactions </li></ul><ul><ul><li>Explosion </li></ul></ul>
  3. 3. Measuring Rate of Reactions <ul><li>Some rate of reactions have detectable change with respect to time </li></ul><ul><li>Changes that are observable like </li></ul><ul><ul><li>When a volume of gas is given off </li></ul></ul><ul><ul><li>When this is a change in mass during the reaction </li></ul></ul><ul><ul><li>When there are temperature changes </li></ul></ul><ul><ul><li>When there are colour changes </li></ul></ul><ul><ul><li>When a precipitate forms </li></ul></ul><ul><ul><li>When there are pH changes </li></ul></ul>
  4. 4. Collision Theory <ul><li>For a reaction to occur </li></ul><ul><ul><li>The reacting particles must collide into each other </li></ul></ul><ul><ul><li>The reacting particles must possess enough activation energy </li></ul></ul><ul><li>Once products are formed, effective collisions have occurred </li></ul>
  5. 5. Factors affecting Rate of Reactions <ul><li>Temperature of the substances used (reactants) </li></ul><ul><li>Concentration of the substances used (reactants) </li></ul><ul><li>Pressure on the reaction </li></ul><ul><li>Particle size (surface area) of the substances used (reactants) </li></ul><ul><li>Presence of catalyst </li></ul>
  6. 6. Temperature <ul><li>Rate of reaction increases with increasing temperature </li></ul><ul><li>High temperature, particles have greater heat energy </li></ul><ul><li>Particles move faster with greater kinetic energy </li></ul><ul><li>Leading to more collisions between particles </li></ul><ul><li>Increased probability of effective collision </li></ul><ul><li>Reactions take place faster </li></ul><ul><li>Speed of reaction doubles when the temperature rises by 10  C </li></ul>
  7. 7. Temperature Amt of product formed Time Higher temperature Lower temperature
  8. 8. Concentration <ul><li>Rate of reaction increases with increasing concentration </li></ul><ul><li>Higher concentration, more reacting particles are present </li></ul><ul><li>Greater probability of an effective collision </li></ul><ul><li>Faster rate of reaction </li></ul>
  9. 9. Concentration – Same no. of moles Amt of product formed Time/s Higher concentration Lower concentration
  10. 10. Concentration – Different no. of moles Amt of product formed Time/s Higher concentration Lower concentration
  11. 11. Pressure <ul><li>Rate of reaction increases with increasing pressure </li></ul><ul><li>Higher pressures, reacting particles are closer together </li></ul><ul><li>Increasing concentration per unit volume </li></ul><ul><li>Greater probability of an effective collision </li></ul><ul><li>Faster rate of reaction </li></ul>
  12. 12. Pressure Amt of product formed Time/s Higher pressure Lower pressure
  13. 13. Particle Size <ul><li>Rate of reaction increases when particle size decreases </li></ul><ul><li>Smaller particles has greater surface area than larger particles of the same mass </li></ul><ul><li>Greater surface area for collision by another reacting particle </li></ul><ul><li>Greater probability of an effective collision </li></ul><ul><li>Faster rate of reaction </li></ul>
  14. 14. Particle size Amt of product formed Time/s Smaller particle size Larger particle size
  15. 15. Catalyst <ul><li>Presence of catalyst increases rate of reaction </li></ul><ul><li>(Presence of inhibitors decreases rate of reaction) </li></ul><ul><li>Catalysts lower activation energy of reactants </li></ul><ul><li>Aids the formation of unstable intermediate products </li></ul><ul><li>Increases probability of formation of products </li></ul><ul><li>Faster rate of reaction </li></ul>
  16. 16. Catalyst Amt of product formed Time/s Use of catalyst Absence of catalyst
  17. 17. Catalyst Energy Time/s Use of catalyst Absence of catalyst E a E a
  18. 18. Catalyst <ul><li>Definition: A substance which increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy but remains unchanged at the end of the reaction </li></ul>

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