**Part
6: THERMODYNAMICS**

This should have been a reasonably straight forward calculation, but care needs to be taken to get the right structures and the right molecular formula, then do the math correctly.

**a. ** C

**b.** DHf **iii** = -1230.9 - (- 1214.3) = -16.6 kcal/mol (2 marks)

**c**. DHc **i** = -1230.9 - (- 35.4) = -1195.5 kcal/mol (1 mark)

DHc **ii** = -1230.9 - (- 26.4) = -1204.5 kcal/mol (1 mark)

**d**. (5 marks)

**e**. Isomer **iii ** is the only chiral molecule. Neither **i ** nor **ii **are chiral because both have at least one plane of symmetry OR because neither have an sp3 C atom with 4 different groups attached(2 marks)

**f.** A bicyclo[2.2.1] system requires a two ring system where there are 2 "bridges" with 2 C atoms and 1 bridge with 1 C atom (1 mark)

**Common errors**:

- incorrect coefficients in the balanced equation
- wrong sign in calculated values
- calculation error (
*e.g.*based on number of H atoms rather than H_{2}molecules*i.e*. using 14 H instead of 7 H_{2}) - incorrect or no labelling of the most and least stable isomers
- incorrect understanding of chirality and the requirements for it
- drawing an isomer of
C_{8}H_{14}that did not fit the required molecular formula or was not a bicyclo[2.2.1] structure - incorrect use of the words atom or molecule