Thermochemistry

• exothermic definition?

  • reaction that gives out energy and heats the surroundings
  • enthalpy change value is negative
• endothermic definition?

  • reaction that takes in energy and cools the surroundings
  • enthalpy change value is positive
• relationship between temperature and enthalpy change?

  • temperature change is matched by an enthalpy change of the same size
• what is enthalpy?

  • sum of a system's internal energy
• what kind of process us bond breaking?

  • endothermic
• what kind of process is bond making?

  • exothermic
• bond enthalpy calculation?

  • energy to break bonds - energy released when bonds are made (break - make)
• How to determine enthalpy change of combustion?

  • measure 100cm3 of water into a calorimeter/beaker
  • weight a spirit burner containing one of the alcohols
  • take the temperature of the water
  • heat the water with the spirit burner
  • stop heating after a reasonable temperature rise
  • measure the final temp of the water
  • reweigh the spirit burner
  • calculate energy given out by the spirit burner and amount of alcohol burnt in mol, then calculate enthalpy change
• What does Hess' Law state? ( WONT BE ASKED TO STATE IN EXAM)


  • the enthalpy change for a reaction is independent of the route taken