Energy changes

• an exothermic reaction is one which transfers energy to the surroundings, usually by heating. This causes a rise in temperature.
• an endothermic reaction is one which takes in energy from the surroundings, this is shown by a fall in temperature
• examples of exothermic reactions -

  • combustion
  • neutralisation
• examples of endothermic reactions -

  • thermal decomposition
  • photosynthesis
• exothermic energy profile -

  
• Endothermic reaction profile -

  
• particles must collide with sufficient energy in order to react
• the activation energy is the minimum energy required for particles to collide
• increasing the temperature increases the rate of reaction, this is because the particles move faster so they collide more frequently and with more energy
• increasing the concentration and pressure increases the rate of reaction, this is because there is a higher volume of particles in a smaller space so collisions will be more frequent
• increasing surface area increases rate of reaction, this is because the same volume of a solid will have more area to collide on
• using a catalyst can increase the rate of reaction by decreasing the activation energy, and they are not used up