Tengo un libro por ti. Gracias por el libro. Why is it Tengo un libro para ti instead of por?

Question

My mom taught me that when you are thanking someone for something you always say gracias por. That makes sense because someone exchanged something to you by giving you something and you are thanking them for exchanging something to you. Por is used for exchanges. Then I said Tengo un libro por ti and my mom corrected me saying para ti. That makes no sense because I have a book for someone which means I am going to exchange this book to them by giving it to them. Por is used for exchanges. Tengo un libro por ti. Gracias por el libro. I need an explanation for why it is Tengo un libro para ti instead of por because para is not used for exchanges. Para actually translates to in order to. Like this: Necesito un lapiz para hacer mi tarea. Please help me.

Answer 1

para is used to give the book to someone

por is used when the act is done for someone, on their behalf, but not to give it to them

por is associated with the cause of an event. Estoy trabajando por Juan, if Juan called in sick and I covered for him.

para is for the effect of an event. Trabajo para Juan. Juan is my supervisor.

por is travel through, a medium, like a door Salimos por la puerta. para is travel to the destination.

viajamos para los angeles.

duration vs. deadline

conduje por dos horas. I drove for two hours

estos deberes son para lunes this homework is for Monday.

look at how the word is used, just looking at the definition will be confusing

English is worse. Do you say I am at home or I am in the house?