Flame-photometric determination of the standard enthalpies of formation of Al(OH)2 and AlO

Abstract

Spectrophotometric studies have been made of gas-phase aluminium-containing species in fuel-rich premixed laminar atmospheric-pressure H₂+ N₂+ O₂ flames to which this metal is added. The principal compound formed by Al under the conditions of this work is Al(OH)₂. Standard zero-point enthalpy changes and equilibrium constants are determined for two important reactions: Al + 2H₂O ⇌ Al(OH)₂+ 2H; ΔH^°₀=–95 ± 30 kJ mol^–1, K= 3.0 exp (4300/T);, Al + OH ⇌ AlO + H; ΔH^°₀=–172 ± 20 kJ mol^–1, K= 0.67 exp (19200/T). The results lead to standard zero-point enthalpies of formation for Al(OH)₂(g) and AlO(g) from Al(g), O₂(g) and H₂(g) of –1005 ± 30 and –349 ± 20 kJ mol^–1 respectively.