rates of reaction

• rates of reaction 6 marker

  in order to react particles must collide with sufficient energy. the minimum amount of energy that particles must overcome to react is called the activation energy. in order to react, particles must be in the correct orientation. the higher the frequency of collisions, the greater the chance of successful collisions. catalysts change the rate of chemical reactions but are not used up during the reaction, different reactions need different catalysts: enzymes act as catalysts in biological systems.
• catalysts job


  catalysts increase the rate of reaction by providing a different route for th reaction that has a lower activation energy.
• marble chip practical ROR

  • the larger the marble chips, the lower the surface area, the slower the rate of the reaction.
• effect of surface area on ROR

  • the larger the SA, the faster the rate of reaction. there are more particles exposed and able to react, therefore higher frequency of collisions.
• temperature on ROR


  as the temp increases, the rate of reaction increases. the thermal energy increases so so does the kinetic energy. there is higher frequency of collisions. the particles overcome the activation energy leading to successful collisions.
• concentration on ROR


  the rate of reaction will decrease as there are less particles in a fixed volume, lowers frequency of reactions.
• ROR equation 


  mean rate of reaction = mass of products used up / time
• change in y/ change in x = ROR
• factors affecting rates of reaction

  • temperature
  • surface area
  • catalyst
  • concentration
• how do reversible reactions reach equilibrium?

  • as reaction occurs, their concentration falls so the forward reaction slows. however when more products are made and concentration rises, the backward reaction speeds
  • when the system reaches equilibrium, both the forwards and backwards reactions go at the same rate
  • the concentrations of the reactants and products do not change
  • only possible if in a closed system
• what is a closed system?

  • a system where none of the reactants or products can escape and nothing else can enter