Write examples of coordination metal complexes in biology.(ii) Calculate the work done in oxidation of 2 moles of SO2 at 298K, if SO2(g) + ½ O2(g) → SO3(g) [ Given : R = 8.314 J/K/mol ]

Answer: (i) Chlorophyll, haemoglobin, vitamin B₁₂ and others. (ii) \(W = +2477.6\) J \(\approx +2.48\) kJ (work is done on the system).

(i) Examples of metal complexes in living systems:

• Chlorophyll – a complex of Mg²⁺; green pigment of plants needed for photosynthesis.
• Haemoglobin – contains the Fe²⁺ complex haem; carries oxygen in blood.
• Vitamin B₁₂ (cyanocobalamin) – a complex of cobalt.
• Enzymes such as carbonic anhydrase contain Zn²⁺.

(ii) For 2 moles of SO₂: 2SO_2(g) + O_2(g) → 2SO_3(g).

\(\Delta n_g = n_{\text{products}} - n_{\text{reactants}} = 2 - (2 + 1) = -1\) mol.

The positive sign shows that work is done on the system, because the volume of gas decreases (compression) during the reaction.