Learn French: Ce problème inattendu s'est évaporé en l'espace d'un jour. - This unexpected problem evaporated within the space of a day.

Both en un jour and en l'espace d'un jour describe how long an action takes to complete. However, en l'espace de emphasizes the brevity or the strict confines of the timeframe, much like 'in the space of' or 'within' in English. It adds a bit of dramatic flair to how quickly the problem disappeared.

Why is the verb s'est évaporé reflexive here?

S'évaporer is a pronominal verb here used in a spontaneous sense. While water literally evaporates, when used figuratively like this, it means 'to vanish'. The reflexive pronoun s' (from se) shows that the action happened to the subject itself, without a specific outside agent causing it.

Is inattendu related to the verb attendre?

Yes! Attendu is the past participle of attendre, which means 'to wait for' or 'to expect'. By adding the negative prefix in-, it becomes inattendu, meaning 'unexpected'.

Could I say en l'espace d'une journée instead of en l'espace d'un jour here?

Yes, you could use d'une journée. While un jour simply counts the unit of time as a single day, une journée emphasizes the duration or the passing of that day. In this context, both work perfectly to express that the problem vanished within a 24-hour period.