Eu passei pelo pedágio sem perceber, porque estava pensando na redação.

Because passar por is the usual expression for to go through / to pass by a place.

• por + o = pelo
• So pelo pedágio literally means through the toll booth / past the toll point

Examples:

• Passei pelo banco. = I passed by the bank.
• Passei pela ponte. = I went over / through the bridge area.

If you said no pedágio (em + o = no), that would sound more like at the toll booth, focusing on location rather than the act of passing through it.

Pedágio can mean:

• the toll itself (the fee)
• the toll booth / toll plaza / toll point, depending on context

In this sentence, it most naturally refers to the toll booth or toll point the speaker went through.

So passei pelo pedágio is something like:

• I went through the toll booth
• I passed the toll plaza

Passei is the pretérito perfeito (simple past / preterite) of passar.

Here it means a completed action:

• Eu passei = I passed / I went through

This tense is used for an event seen as finished:

• Eu passei pelo pedágio = I went through the toll booth.

Because estava pensando describes an ongoing background action in the past.

• passei = the main completed event
• estava pensando = what was going on at that time

So the sentence structure is:

• I went through the toll booth without noticing, because I was thinking about the essay.

If you said pensei, that would sound like I thought as a completed event, not an ongoing mental state in the background.

This contrast is very common in Portuguese:

• pretérito perfeito for the finished action
• imperfeito or imperfect progressive for background context

Sem + infinitive is a very common way to say without doing something.

So:

• sem perceber = without noticing / without realizing

Other examples:

• Sai sem falar nada. = He left without saying anything.
• Ela foi embora sem me avisar. = She left without warning me.

In your sentence, sem perceber means the speaker passed the toll booth and did not notice it at the time.

Here perceber means to notice or to realize, not just to perceive in a literal sensory way.

So:

• sem perceber = without noticing
• sometimes also without realizing

In Brazilian Portuguese, perceber often has that everyday meaning:

• Você percebeu? = Did you notice?
• Não percebi. = I didn’t notice / I didn’t realize.

Because here it means because, introducing a reason.

Portuguese has four forms:

• porque = because
• por que = why / for what reason
• por quê = why, usually at the end of a question
• porquê = the reason (a noun)

In your sentence:

• porque estava pensando na redação = because I was thinking about the essay

So porque is the correct one.

Because na is the contraction of:

• em + a = na

The noun redação is feminine, so with the article a:

• na redação = in the essay / about the essay

But in natural English, we would usually translate it as:

• thinking about the essay
• thinking about my composition / writing assignment

The preposition with pensar is often em in Portuguese:

• pensar em algo = to think about something

So:

• estava pensando na redação literally = was thinking in/on the essay
• natural meaning = was thinking about the essay

In Brazilian Portuguese, redação often means:

• essay
• composition
• writing assignment

This is especially common in school contexts.

Examples:

• Preciso fazer uma redação. = I need to write an essay.
• A redação do ENEM = the essay section of the ENEM exam

It can have other meanings in different contexts, like editorial office / newsroom, but in this sentence the school-style meaning essay/composition is the most likely one.

Not always. Portuguese often drops subject pronouns when the verb already makes the subject clear.

So both are possible:

• Eu passei pelo pedágio...
• Passei pelo pedágio...

Because passei clearly means I passed, the pronoun is optional.

Including eu can:

• add emphasis
• improve clarity
• sound a bit more explicit

So here Eu is correct, but not required.

Yes, but the meaning changes slightly.

• sem perceber sounds smooth and natural: without noticing
• e não percebi means and I didn’t notice

Both are understandable, but sem perceber is more idiomatic in this kind of sentence.

Compare:

• Passei pelo pedágio sem perceber. = I went through the toll booth without noticing.
• Passei pelo pedágio e não percebi. = I went through the toll booth and didn’t notice.

The first version connects the two ideas more tightly.

Yes. Passar is a very common verb with many meanings, and one of them is to pass by / go through.

Some common uses:

• passar por = to go through / pass by
• passar em = to stop by / to pass in an exam, depending on context
• passar de = to exceed / go beyond
• passar o dia = to spend the day

In this sentence:

• passar pelo pedágio = to go through the toll booth / pass the toll point

So this is a very useful everyday pattern to learn:

• passar por + place

Yes. Portuguese allows some flexibility.

For example:

• Porque estava pensando na redação, eu passei pelo pedágio sem perceber.
• Eu passei pelo pedágio sem perceber porque estava pensando na redação.

The original version sounds very natural. Putting the porque clause at the end is common because it gives the reason after the main event.

The original word order is probably the most neutral and conversational.