Thermochemical Cycles

Question 1

Using a Thermochemical Cycles

Answer 1

1) write equation for reaction
2) write down elements in the two compounds with the correct quantities of each
3) Put in the /\fH values with the arrows showing the direction - from elements to compounds
4) Put in the arrows to go from starting materials to products via the elements
5) Reverse the sign of /\fH if the red arrow is the opposite direction to the black arrow
6) go round the cycle in the direction of the red arrows and add up the /\H values as you go

Question 2

Using enthalpy diagrams

Answer 2

1) Draw a line a level 0 to represent the elements
2) Look up the values of /\fH for each compound and enter these on the enthalpy diagrams, taking account of the signs, negative values are below 0, positive values are above
3) ind the difference in levels between the two compounds. This represents the difference in their enthalpies
4) /\H is the difference in levels taking account of the direction of change. Up is the positive and down is negative.