Rate of reaction

• Chemical reactions


  Occur when there is enough energy to break the bonds that hold the particles together in a molecule
• Reaction rate


  The speed at which a reaction proceeds, how long a reaction takes to finish
• The rate of a reaction can vary
• Reaction example

  • Combustion - quick, causing an explosion in seconds
  • Rust forming on an old boat - slow
• Reactions occur


  1. Particles interact, specifically when they collide

  2. In a particle collision, electrons can be rearranged depending on the energy involved

  3. If the energy of a collision is high enough, the particles can break their bonds or form new bonds and reform as different substances
• These collisions will happen constantly during a reaction as the reactants turn into the products
• Effective collision


  Requires reactants to have enough energy to react/collide
• The time it takes for reactants to fully react and turn into products depends on the number of collisions occurring every second
• If there aren't many collisions, the reaction will be slow. If there are a lot, the reaction will be fast!
• Almost every reaction can be sped up or slowed down
• Rate of reaction


  The speed in which new particles form
• Activation energy


  The least amount of energy needed in order to get the molecules to react
• Factors that can affect the rate of a reaction

  • Temperature
  • Concentration
  • Surface Area
  • Inhibitor or catalyst
  • Agitation
• Temperature


  The higher the temperature the faster the rate of reaction because as the temperature rises the particles of the reactants move more quickly which causes the particles to collide more often and with greater energy
• Concentration


  A higher concentration of reactants will cause a faster rate of reaction. The particles are closer together when the concentration is high which increases the frequency of collisions between reactants
• Surface area


  Increasing the surface area of solid reactants increases the rate of reaction. If a solid is ground into a fine powder then it will have a greater surface area exposed which will increase the frequency of collisions between the reactants and speed up the reaction
• Inhibitor


  A substance that slows down the rate of a reaction
• Catalyst


  A substance that speeds up a reaction by lowering the activation energy of a reaction
• Examples of catalysts in our body are enzymes which can speed up chemical reactions such as respiration, digestion, and protein synthesis
• The surface area of a solid is "the area of the outer part or uppermost layer of something"
• When the surface area of the tablet was whole it took longer to dissolve then when it was completely crushed
• The larger the surface area


  The slower the rate of reaction
• Collisions are required for a reaction to occur. More reactants colliding per second means the rate of reaction will increase
• Reactions can go any speed
• Reactants need enough energy to react and reactants need to collide with each other for a reaction to occur
• Metal rusting and plants decomposing are examples of slow reactions
• Collision theory


  A model explaining the mechanism of chemical reactions and their rate. Collision theory predicts that the rate of reaction will be proportional to the number of effective collisions
• Effective collisions


  Defined by correct particle orientation and collision energy greater than the activation energy of the reaction
• The rate of reaction is proportional to the number of effective collisions
• The reaction progress can be plotted in a potential energy diagram, with the transition state being the highest energy state of the system
• Increasing concentration


  Increases the number of particles in a given volume, so they are more likely to collide, so reaction rate increases
• Increasing pressure in a gas

  Means the particles are pushed closer together, so they are more likely to collide, so the reaction rate increases
• Increasing surface area


  Increases the number of reactant particles exposed to collisions, so again the reaction rate increases
• For a reaction to occur, reactants need to collide with enough energy to react
• How often reactants collide depends on the motion of the reactants; for example, smaller reactants tend to be smaller but move faster
• The amount of energy required to react is different for every reaction, some reactants are very easy to turn into products and only need a small amount of energy, while other reactants might require considerably more energy to proceed