There are two crystalline forms of PbO; one is yellow and the other is red. The standard enthalpies of formation of these two forms are – 217.3 and – 219.0 kJ mol-1 respectively. Calculate the enthalpy change for the solid-solid phase transition: PbO (yellow) → PbO(red)
Our aim is PbO (yellow) → PbO (rpd); ΔH =? Given (i) PbO(s) + 1202(g) ) → PbO (yellow); ΔH = – 217.3 kJ mol-1 (ii) Pb(s) + 12O2(g) ) → PbO(red); ΔH = —219.0 kJ mol-1 Subtracting (1) from (ii), we get PbO (yellow) → PbO(red); ΔH =- 219.0 – (- 2173) = – 1.7 kJ mol-1.
