La sala está completamente vacía.

Because vacía describes a state or condition, not an essential characteristic.

In Spanish, estar is commonly used for things like:

• location
• temporary conditions
• resulting states

So La sala está completamente vacía means the room is empty right now / in this situation.

Using ser here would sound unnatural in normal Spanish.

Because vacía is an adjective, and it has to agree with sala, which is a feminine singular noun.

Agreement here is:

• la sala → feminine singular
• vacía → feminine singular

Compare:

• El salón está vacío.
• La sala está vacía.
• Las salas están vacías.

Sala can mean room, hall, or sometimes living room/lounge, depending on context.

In Spain:

• salón is often more common for living room
• sala can sound a bit more general or formal, like room, hall, waiting room, ward, etc.

So the exact English translation depends on the situation.

La means the and shows that we are talking about a specific room.

So:

• La sala = the room / the hall / the living room

If you removed the article and said just sala, it would usually be ungrammatical in this kind of sentence.

Completamente is an adverb meaning completely. It modifies vacía.

So:

• vacía = empty
• completamente vacía = completely empty

It adds emphasis, saying that the room is not just empty, but totally empty.

Yes. That is perfectly natural.

• La sala está vacía = The room is empty.
• La sala está completamente vacía = The room is completely empty.

The second version is just stronger or more emphatic.

Usually, the most natural place is before the adjective:

• La sala está completamente vacía.

That is the standard and most natural wording.

You may sometimes hear other word orders for emphasis, but for a learner, it is best to stick with:

• estar + completamente + adjective

It is pronounced roughly va-CEE-a.

The accent mark on í shows that the i is stressed and pronounced separately from the a:

• va-cí-a → three syllables

Without the accent, Spanish spelling rules would suggest a different pronunciation.

Yes. Totalmente vacía is also correct.

Both mean completely empty. In many contexts, they are interchangeable:

• La sala está completamente vacía.
• La sala está totalmente vacía.

Completamente may sound a bit more neutral and standard here, but both are natural.

It describes the room’s condition, not its location.

Even though estar is also used for location, here it is being used for state:

• La sala está vacía = The room is empty.
• La sala está arriba = The room is upstairs.

So in this sentence, estar means to be in a certain condition.

Yes, but it is not exactly the same structure.

• La sala está completamente vacía focuses on the state of the room.
• No hay nada en la sala means There is nothing in the room, which focuses on what is inside it.

They are very close in meaning, but not identical in wording or emphasis.

Yes, it is natural and correct in Spain Spanish.

A native speaker in Spain might also say:

• El salón está completamente vacío if they specifically mean the living room
• La habitación está completamente vacía if they mean the bedroom / room

So your sentence is good, but the exact noun may change depending on what kind of room is meant.