Passive se

Hi,

the store opens at ten

la tienda se abre a las diez

Se abre la tienda a las diez

i believe you can use this sentence either way , , please advise.

but my main question is why not just say la tienda abre a las diez

why the se

like with 

what time does that restaurant open 

a que hora se abre ese restaurante , why the se , can the sentence be used without.

and in the sentence

when a car breaks down on the freeway

cuando se estropea un carro en la autopista

i thought estropearse was reflexiv , why is it passive se

thank you for your time.

¡Hola VR143!

My apologies for the late reply! I've broken my answer up into three sections to try to keep everything clear:

1) Can you say both La tienda se abre a las diez and Se abre la tienda a las diez for "The store opens at ten"?
 

Yes, it's possible to say this sentence either way. The first would be the most natural/neutral version, while the second would be less common - it puts a bit more emphasis on se abre. (See the answer below for a note on using se here!)
 

2) Can you use just abre instead of se abre in sentences like these?
 

Yes, when you're talking about an establishment (e.g. a store, a restaurant, etc.) opening, you can use abre instead of se abre. In fact, many native speakers would find the version without se a bit more natural, since this se is passive and adds a passive meaning that isn't really necessary here. (So, La tienda abre a las diez is closer to "The store opens at ten," while La tienda se abre a las diez is closer to "The store is opened at ten.")
 

3) Why is estropearse the passive se?
 

The se in estropearse is the reflexive se rather than the passive one. Without the reflexive pronoun, estropear just means "to break / to damage"; with the reflexive pronoun, the verb takes on the meaning "to break down."

I hope that all of this helps! Do let me know if any of it is still unclear!

Saludos,

Liss