Q: I purchased a Barcelona Card when I visited Barcelona in January. I did not validate it or use the card. Will my unused Barcelona Card expire? If it will expire, when?
A: If you have not activated your Barcelona Card (i.e. you have never used it) you will be able to use it on your next visit to Barcelona provided your visit is within the same year when you first picked up your card in Barcelona. Therefore if you purchased and picked up your card in January the card will expire at midnight of 31st December of the same year. This means if you have an unused 5 day Barcelona card which you bought in Barcelona you would have to have used all 5 days before the Midnight on the 31st December of the same year on which you picked up your card.
Notice that I used the words "picked up" and not "purchased". The reason is that you can purchase a Barcelona Card voucher online any time in advance of your trip (even the year before you want to use it) and the card start time for use will only begin within the same year after the date you actually picked up the card in Barcelona and not the year of purchase of the online voucher. If you don't use your Barcelona Card after you pick it up then it will be active until Midnight of 31st December of the same year of pickup.