Si el frasco está vacío, lo reutilizo para guardar arroz.

Because empty is treated as a state here, not a permanent characteristic.

• estar is used for temporary conditions or resulting states: El frasco está vacío = The jar is empty
• ser is used for identity or more inherent qualities.

So está vacío means the jar happens to be empty at that moment or in that situation.

Lo is a direct object pronoun meaning it. It refers back to el frasco.

• el frasco is masculine singular
• so the pronoun is lo

So:

• reutilizo el frasco = I reuse the jar
• lo reutilizo = I reuse it

Spanish often uses object pronouns to avoid repeating the noun, just like English uses it.

In Spanish, object pronouns normally go before a conjugated verb.

So:

• Lo reutilizo = correct
• Reutilizo lo = incorrect

This is the standard position with a normal finite verb.

Reutilizar means to reuse. It is a very natural verb for using something again, especially for containers, materials, packaging, and household objects.

So lo reutilizo means:

• I reuse it
• more literally, I use it again

You could also hear:

• lo vuelvo a usar = I use it again

But reutilizar is compact and very common in this kind of context.

Because this sentence expresses a habit, general rule, or regular practice:

• If the jar is empty, I reuse it to store rice

It is not talking about one specific future event. It means something like whenever that happens, that is what I do.

This pattern is very common in Spanish:

• Si tengo tiempo, leo.
• Si llueve, me quedo en casa.

So the present tense here is not strange at all.

Si means if, so it introduces a condition.

• Si el frasco está vacío... = If the jar is empty...

Cuando means when, and it suggests the event is expected rather than conditional.

Compare:

• Si el frasco está vacío, lo reutilizo = If the jar is empty, I reuse it
• Cuando el frasco está vacío, lo reutilizo = When the jar is empty, I reuse it

In many everyday contexts, both could work, but si focuses more on the condition being met.

Because the sentence begins with a subordinate clause:

• Si el frasco está vacío, ...
• then the main clause: lo reutilizo para guardar arroz

In Spanish, when this kind of clause comes first, a comma is normally used. It helps separate the condition from the main action.

Because arroz is being used here in a general, uncountable sense: rice as a substance.

• guardar arroz = store rice
• guardar el arroz would usually mean store the rice, referring to some specific rice already known in the conversation

So without the article, it sounds more general and natural here.

Para means for or in order to, and guardar means to keep, to store, or sometimes to put away.

So:

• para guardar arroz = to store rice / for storing rice

It explains the purpose of reusing the jar.

Because vacío has to agree with el frasco, which is:

• masculine
• singular

So the adjective must also be masculine singular:

• el frasco vacío

If the noun were feminine, you would use vacía:

• la botella vacía

Frasco usually refers to a jar, small container, or sometimes a bottle, often made of glass or plastic.

Depending on context, English might translate it as:

• jar
• container
• bottle

In this sentence, jar is probably the most natural translation if it is being reused to store rice.

Yes. Both are possible:

• Si el frasco está vacío, reutilizo el frasco...
• Si el frasco está vacío, lo reutilizo...

But repeating el frasco sounds less natural, because Spanish usually prefers the pronoun once the object is already clear. So lo reutilizo is smoother and more natural.

Here it clearly means store or keep.

Guardar can mean different things depending on context:

• guardar dinero = save money / keep money
• guardar ropa = put away clothes / store clothes
• guardar arroz = store rice

So in this sentence, store is the best choice.

Most naturally, it sounds like a habit or usual practice.

• If the jar is empty, I reuse it to store rice

That sounds like this is what I normally do.

If you wanted a clearer one-time future meaning, Spanish would often use a different structure, for example:

• Si el frasco está vacío, lo reutilizaré para guardar arroz = If the jar is empty, I’ll reuse it to store rice

So the original sentence is most naturally read as habitual.