Rates of Reactions

• Reactants


  The initial substances at the beginning of a chemical reaction.
• Product 


  the new substances formed as a result of a chemical reaction
• Chemical reaction

  a process where reactants transform into products, involving the breaking and forming of chemical bonds.
• The Rate of Reaction

  The speed at which a chemical reaction occurs, measured by how quickly reactants turn into products.

  A fast reaction is one which is done in moments such as combustion.

  A slow reaction is one which takes days, months or even years to complete such as corrosion.

  The rate of reaction= amount of reactant used or product formed / time
• Collision theory of chemical reaction


  For a chemical reaction to occur, the atoms, ions or molecules must collide with enough energy to occur.
• 3 Requirements for a successful collision


  Activation energy:

  The energy needed for the molecules to join in a reaction. The reaction will occur if a collision occurs with more energy than the activation energy. ie. If the collision has sufficient energy to overcome the activation energy barrier.

  Collisions:

  The reactants must collide

  Orientation:

  Have to be at the right angle, the molecules need to be at the right place and fit together correctly.
• Methods in changing the rate of a reaction

  Temperature

  Increasing the pressure of gasses

  Concentration of solution

  Catalyst

  State of subdivision / surface area

  Agitation ( Mixing / stirring )
• Temperature


  If you increase the temperature the molecules heat up and move quicker which increases the number of collisions per second. It also means that far more particles have energy greater then the activation energy. The amount of successful collisions greatly increase, increasing the rate of reaction
• Increasing the pressure of gases


  When gases react, when the pressure is increased there is less space for the molecules to move and more collisions per second.
• Concentration of solution


  If the concentration of a solution is increased there is more reactant particles in the same volume so more collisions per second.
• Catalyst


  A chemical which speeds up the reaction but is not used up by the reaction. Catalysts make it easier for collisions to occur by providing an ideal site for collisions to occur at. They lower the activation energy by providing an alternative pathway. Examples of catalysts in everyday life:

  • Saliva: Enzyme in saliva is called amylase which speeds up the process of breaking down food.
• State of subdivision / surface area


  The surface area is the total area exposed to possible collisions
• Agitation ( Mixing / stirring ) 


  As a chemical reaction proceeds, the particles of the reactants get used up.

  When there are fewer particles of reactants, there are fewer collisions and so the reaction rate slows.

  To maintain the reaction rate, the products of the reaction should be removed and replaced with more particles of reactants.

  A basic way of doing this is stirring or mixing the reactants

  Agitation prevents the build up of products around the reactant