Question

Derive relationship between \( \Delta H \) and \( \Delta U \) for gaseous reaction. Define: Vulcanization. What is peptide bond?

Hint:

Use \( \Delta n_g \) to relate \( \Delta H \) and \( \Delta U \); vulcanization enhances rubber properties; peptide bonds are amide linkages in proteins.

Answer 1

i. Relationship between \( \Delta H \) and \( \Delta U \): Enthalpy \( H = U + PV \). For a gaseous reaction at constant T, \( \Delta H = \Delta U + \Delta (PV) \). Using ideal gas law, \( PV = nRT \), so: \[ \Delta H = \Delta U + \Delta (n_g RT) = \Delta U + \Delta n_g RT, \] where \( \Delta n_g \) is the change in moles of gas, \( R = 8.314 \, \text{J K}^{-1} \text{mol}^{-1} \), T is temperature in K.
ii. Vulcanization: The process of heating natural rubber with sulfur to form cross-links between polymer chains, improving elasticity, strength, and durability.
iii. Peptide Bond: A covalent bond (\( -\text{CO}-\text{NH}- \)) formed between the carboxyl group of one amino acid and the amino group of another, with loss of water, linking amino acids in proteins.