終わる and 終える: an event ending and completing work
Compare an event ending with completing a task, while noting that 終わる can also take を, and distinguish completion from interruption.
Ask when an event ends
授業は何時に終わりますか。 asks what time the class ends. 終わる, read おわる, can describe an event or activity reaching its end.
授業が終わってから、図書館に行きます。 means that the speaker will go to the library after class ends. The end of class precedes the visit rather than overlapping it.
A person completes a task
午前中に仕事を終えました。 says that the speaker finished work during the morning. 終える, read おえる, takes を for the task completed and has the te-form 終えて.
準備を終えて、客を迎えました。 says that someone completed the preparations and welcomed the guests. It does not merely say that preparation began or was interrupted.
を does not automatically make 終わる wrong
これで説明を終わります。 can announce the end of an explanation. 終わる also has a use for bringing something to an end, so を＋終わる is not automatically incorrect.
作業を途中でやめました。 says that someone stopped working partway through. Unlike completing work in 仕事を終えました, it does not establish that the required task was finished.
Must これで説明を終わります be wrong because it contains を?
Show the answer and why
No. 終わる can also mean bringing something to an end, making this a valid closing announcement. Its structure differs from 授業が終わる, where the class itself ends.