The 23-year-old spent last season at Stoke and suffered relegation from the Premier League.
"It is important that the club want to fight for something".
Barcelona said they reserve the right to buy Mina back, while Gomes has cost Everton a £2m loan fee.
Silva has been desperate to bolster Everton's defence all summer and had been linked with a number of targets, such as Manchester United's Marcus Rojo and Newcastle's Jamaal Lascelles, but Mina was his top target.
"The English club will pay FC Barcelona 2.25 million euros for the season long loan and will also pay the player's wages".
Mina had always been linked with a move away from Barcelona this summer with the club's purchases of non-EU players in Malcom, Arthur and Arturo Vidal filling their quote per La Liga's rules.
The free signing of Brazilian midfielder Bernard was confirmed after a work permit was granted.
The Premier League club also parted company with Ramiro Funes Mori, Wayne Rooeny and Davy Klaassen among others in the summer transfer window.
"I spoke to Lucas and he told me all about the club, which also made me keen to come here". When I found out about this opportunity and what the manager wanted out of me I was happy.
"I have spoken a lot to the coach and I know his passion for Everton and determination to be successful".