Representing thermochemical cycles

• Can use enthalpy diagrams instead of thermochemical cycles
• The enthalpies of all elements in their standard states are taken as 0.

  This convention means that the standard state of hydrogen is H2 and not H because it exists as H2 at room temperature and pressure
• Using an enthalpy diagram.

  1. Draw a line at 0 to represent elements
  2. Find values for ΔfH for each compound and put on diagram
  3. Find difference in levels
  4. ΔH takes into account the direction of the change
• Using a thermochemical cycle:

  1. Write the equation
  2. Write down elements that make up the compounds
  3. Put ΔH values with arrows in the correct direction
  4. Follow arrows from reactants to products
  5. If going against the arrow, flip the sign