Depois que eu esquentar a sopa, vou comer.

It introduces a time clause meaning after.

A useful pattern is:

• depois que + conjugated verb
• depois de + noun / infinitive

So here, because a whole clause follows — eu esquentar a sopa — depois que is the natural choice.

Compare:

• Depois que eu esquentar a sopa... = a full clause
• Depois de esquentar a sopa... = after heating the soup...

Both can work, but the structure is different.

Here, esquentar is not an infinitive in function. It is the future subjunctive.

Portuguese often uses the future subjunctive after words like:

• quando
• se
• assim que
• depois que

when the action is still in the future.

So:

• Depois que eu esquentar a sopa...

means the heating has not happened yet.

For many regular verbs, the future subjunctive form looks exactly like the infinitive. That is why esquentar can be confusing.

Compare:

• infinitive: esquentar
• future subjunctive: quando eu esquentar, depois que eu esquentar

Same spelling, different grammar role.

That is true: Portuguese often omits subject pronouns when the subject is clear.

But here eu is very helpful because esquentar could also match other subjects in this tense, such as:

• eu esquentar
• você esquentar
• ele/ela esquentar

So adding eu makes the subject explicit and avoids ambiguity.

Without eu, the sentence could sound less clear.

Because ir + infinitive is the most common everyday way to talk about the future in Brazilian Portuguese.

So:

• vou comer = very natural in speech
• comerei = correct, but usually more formal, written, or stylistically marked

A Brazilian speaker would very often choose vou comer in normal conversation.

Because the object is already obvious from context.

In English, we might also leave it out in some situations:

• After I heat up the soup, I’ll eat.

Portuguese does the same thing here. Vou comer is naturally understood as I’ll eat the soup.

If you want to be more explicit, you can say:

• Depois que eu esquentar a sopa, vou comer a sopa.

But that sounds more repetitive than necessary.

Because it refers to a specific soup, not soup in general.

Portuguese uses definite articles very often, often more than English does. So a sopa here means something like the soup — the soup both speaker and listener have in mind.

Without the article, sopa would sound more general or less anchored to a specific situation.

Yes, but the structure changes.

You can say:

• Depois de esquentar a sopa, vou comer.

That uses depois de + infinitive.

You can also hear:

• Depois de eu esquentar a sopa, vou comer.

That uses a personal infinitive.

However, depois que eu esquentar is extremely common and very natural when you want a full clause with an explicit subject.

So all of these are possible, but they are not built the same way.

Yes, comer sopa is completely natural in Brazilian Portuguese.

You may also hear tomar sopa in some contexts, but comer sopa is very normal and idiomatic.

So there is nothing strange about vou comer referring to soup.

Yes.

You can also say:

• Vou comer depois que eu esquentar a sopa.

The meaning stays the same.

The main difference is punctuation:

• Depois que eu esquentar a sopa, vou comer.
  fronted time clause → comma normally used

• Vou comer depois que eu esquentar a sopa.
  time clause after the main clause → usually no comma

Esquentar is very natural in everyday Brazilian Portuguese for heating up / warming up food.

So for soup, esquentar a sopa sounds casual and normal.

Aquecer is also correct, but it can sound a bit more formal, technical, or less conversational depending on the context.

In ordinary speech, many Brazilians would naturally say esquentar.