I still have a few sentences to check.

Thank you very much, Writeacher.

1) I would worl at a passion (my passion), because even if I know it is difficult to take off, I think that the job itself can motivate me.
In fact, I'd prefer to have a job in which I can do what I like.
2)We must keep our cell phones switched off in class (during school hours). We mustn't leave the classroom in the change of the hour. ( in between classes??)

1) I would work at my passion because, even if it is difficult to take off, I think the job itself can motivate me.

In fact, I'd prefer to have a job in which I can do what I like. - OK

2) We must keep our cell phones switched off during school hours.

We mustn't leave the classroom between classes.