8. Methanol (CH₃OH) is an important chemical in industry - Scottish Highers Chemistry - Question 8 - 2016

The structure of compound X is:

   H
   |
H—C—C(CH₃)₂
   |
   CH₃

This represents 2-methylpropene (isobutene), which is suitable for the reaction with methanol.

The atom economy of 100% means that all the atoms from the reactants are converted into the desired product, without any waste products being formed. Essentially, it indicates that nothing is lost in the reaction and that all starting materials contribute to the final product.

To calculate the enthalpy change:

1. Bond Breaking (Energy Required):

   • C–H bonds: 4 bonds at 412 kJ/mol = 412 × 4 = 1648 kJ
   • O–H bonds: 1 bond at 463 kJ/mol = 463 kJ
   • Total for breaking bonds: 1648 + 463 = 2111 kJ

2. Bond Forming (Energy Released):

   • C=O bonds: 1 bond at 743 kJ/mol = 743 kJ
   • H–H bonds: 2 bonds at 436 kJ/mol = 436 × 2 = 872 kJ
   • Total for forming bonds: 743 + 872 = 1615 kJ

3. Enthalpy Change Calculation: $ΔH = ext{Bond breaking} - ext{Bond forming}$ $ΔH = 2111 - 1615 = 496 ext{ kJ/mol}$