**Part
6: THERMODYNAMICS
**

**b**. H_{2}C=C=CHCH_{3}+ 5.5 O_{2} -----> 4 CO_{2} + 3 H_{2}O (2 marks)

**c** calculations are shown on the diagram (4 marks) and **d. **see below (4 marks)

**e**. 1,2-butadiene is H_{2}C=C=CHCH_{3} and 1,3-butadiene is H_{2}C=CHCH=CH_{2}. Therefore 1,3-butadiene has 6 sp2C-H compared to 3 sp2C-H and 3 sp3C-H in the 1,2-isomer. There is also a pi interaction (resonance) between the C2 and C3 in 1,3-butadiene that further stablises the system. (2 marks)

**Common errors**:

- couldn't write a balanced equation
- could not apply Hess's law equation and made algebraic mistakes with the signs of the terms.
- used 6 moles of H2 instead of the required 3.
- couldn't relate calculated stablity to the energy diagram.
- didn't understand the terms heat of combustion or formation in terms of what they represent.
- poorly structured diagram (e.g. products or elements not aligned)
- incomplete rationale of the energy differences of the two dienes.