What is the ruling on disposing of students' money, which was collected for photocopying worksheets, by returning one-third of it to the teacher and spending the remainder on personal matters, given the impossibility of returning it to the students?

The money must be returned to the students, but since that is difficult, the questioner, along with her repentance and seeking forgiveness, should estimate the amount and donate it as charity on behalf of its owners. If it is impossible to return the money due to the absence or death of its owner, one can donate it on their behalf, or multiply good deeds and supplicate to Allah to appease them on the Day of Judgment.