Rates of reaction

• Reaction rates - The rate of a chemical reaction:

  • Rate = change in conc/time

  • Rate = Reactant used or Product made/time

  • If a reaction produces gas the rate can be meaused by measuing the vol of gas produced or decrease in reactants

  • If reactant is an acid measure pH over time
• Reaction Rates - Collision theory:

  •For a reaction to occur particles must collide

  - Colliding particles need enough energy to break exciting bonds

  - Particled must be in the orietation so that the reactive parts of the particles collide

  • As a result only a small proportion collisons result in a reation

  • Activation energy (Ea) = minimum energy for a particle to gave to react
• Reaction Rates - Changing conditions: Concentration

  • Changing conc affects rate

  • If conc is increased there will be more particles in the same space:

  1. The reaction particles are closer together
  2. Collisions are more frequent
  3. The rate increases
• Reaction rates - Changeing concentration: Pressure

  • If pressure is increased there is same number of gas particles in a smaller space increasing conc so the molecules collide more frequently and rate increases
• Reaction Rates - Concentration-Time graph

  • Rate of reaction can be calculated by: Drawing tangent on the curve the measuring gradient of tangent
  • Gradient = Rise/Run
  • Units of rates = moldm-3s-1