Near 2600 K, 10% of water molecules are thermally dissociated at atmospheric pressure, with a reaction time constant below 1 ms. Such temperatures can be reached with focused sunlight. To use this endothermic reaction for the production of hydrogen, the hydrogen must be separated from the oxygen at high temperature, because they would quickly recombine to form water again, if the unseparated mixture were simply returned to lower temperatures. We have considered thermoacoustic mixture separation for this purpose. Our calculations show that the thermal-diffusion ratios are high enough to yield steadily flowing streams of hydrogen-enriched steam and oxygen-enriched steam in a separation channel less than a wavelength long. However, the thermoacoustic power density in 1-bar steam is low, so the required apparatus would be large, needing alot of expensive and fragile high-temperature material, such as calcia-stabilized zirconia. Our estimates show that this approach to solar hydrogen production would be approximately 30 times more expensive than solar-Stirling electricity generation driving traditional water electrolysis. [Work supported by DOE Office of Science.]