Are there achievements in SpaceChem? When I look at the Steam page, it says I've earned 0/15, but doesn't list any. Are they hidden until you stumble onto them?
On the 29th of April 2011 the game received an update.
Among other changes, all the 12 challenges previously only visible in the game, are now also visible Steam achievements, and there are an additional 3 achievements related to a TF2 tie-in.
This accounts for all 15 previously "empty" achievements on Steam.
Additionally, I was awarded Steam achievements for each completed Challenge without having to re-complete them, but I'm not sure of the mechanics in operation here to know how this is managed.
Where are you seeing this 0/15? The SpaceChem store page does not show it having any achievements (there would be an indicator of it below the "Single-player" one in the Game Details box).
Looking on the Steam forums for the game, the developer has said that they'd be coming in a future update, but it doesn't look like the game has received any updates yet.