Learn Hardcore Croatian: Večeras ću isprazniti zdjelu s juhom.

The little word ću is a clitic (an “unstressed” short word) and Croatian clitics normally want to be in second position in the sentence (or clause).

In Večeras ću isprazniti zdjelu s juhom:

Večeras = first word
ću = clitic placed in second position

You can change the word order, but ću still wants a very early place:

Ja ću večeras isprazniti zdjelu s juhom.
Večeras ću isprazniti zdjelu s juhom.
Ispraznit ću večeras zdjelu s juhom.

All of these are grammatical. Notice in the last example the clitic is attached right after the verb: Ispraznit ću… (often the infinitive drops the final -i before ću in this pattern).

Why is it zdjelu and not zdjela?

Zdjela means “bowl” and is a feminine noun.

In this sentence, it is the direct object of the verb (empty what? → the bowl), so it must be in the accusative case.

For most feminine nouns ending in -a:

Nominative (subject): zdjela – “a/the bowl”
Accusative (direct object): zdjelu – “(the) bowl”

So:

Zdjela je na stolu. – The bowl is on the table. (subject → nominative)
Ispraznit ću zdjelu. – I will empty the bowl. (object → accusative)

What does s juhom literally mean, and why is s used here?

S juhom literally means “with soup”.

s = “with”
juha = “soup”
juhom = “with soup” (instrumental case)

Here s is a preposition that usually goes with the instrumental case and often means “with” in the sense of “together with, containing”.

So zdjelu s juhom is literally “(the) bowl with soup” → naturally understood as “the bowl with (some) soup in it” or “the bowl of soup”.

Why is it juhom instead of juha?

Juha (“soup”) is in the instrumental case after the preposition s.

For feminine nouns in -a, the instrumental singular is usually formed with -om:

Nominative: juha – soup
Instrumental: juhom – (with) soup

Because of the preposition s, you must use juhom, not juha:

s juhom – with soup
s vodom – with water
s mačkom – with the cat

What’s the difference between isprazniti and pražniti?

Both are related, but their aspect is different:

isprazniti – perfective: “to empty (completely), to finish emptying”
pražniti – imperfective: “to be emptying, to empty (over time / repeatedly)”

In your sentence:

Večeras ću isprazniti zdjelu s juhom.
→ “Tonight I will empty the bowl (and it will be empty at the end).”

If you said:

Večeras ću pražniti zdjelu s juhom.

it would sound odd here, because it focuses on the ongoing process, not on the completed result. For “finish the bowl of soup”, the perfective isprazniti is the natural choice.

Does isprazniti zdjelu s juhom mean “eat the soup,” or could it also mean pouring it out?

Literally, isprazniti zdjelu s juhom is neutral: it just means “to empty the bowl with soup.”

Context decides how you empty it:

If you’re at the table talking about dinner, it will usually be understood as
“I’ll finish my bowl of soup (by eating it).”
In another context (e.g. cleaning the kitchen), it could mean
“I’ll pour the soup out / throw it away and leave the bowl empty.”

So the verb itself doesn’t say whether you eat it or pour it out; the situation gives that meaning.

Could I say zdjelu juhe instead of zdjelu s juhom? Is there any difference?

Yes, you can also say:

Večeras ću isprazniti zdjelu juhe.

Here juhe is in the genitive case, and zdjela juhe literally means “a bowl of soup”.

Rough nuance:

zdjela s juhom – “a bowl with soup (in it)”
zdjela juhe – “a bowl of soup”

In many everyday contexts, they basically mean the same thing; both are acceptable.
Some speakers might feel zdjela juhe sounds a bit more like a portion (“a serving of soup”), but the difference is subtle.

Are there more natural ways to say “I’ll finish my bowl of soup” in Croatian?

Yes, depending on what you want to emphasize, you might also hear:

Večeras ću pojesti zdjelu juhe. – “Tonight I’ll eat a bowl of soup.”
(focuses on eating, not just emptying)
Večeras ću pojesti svoju juhu. – “Tonight I’ll eat my soup.”
Večeras ću dovršiti juhu. – “Tonight I’ll finish the soup.”

Your original sentence Večeras ću isprazniti zdjelu s juhom is grammatical and understandable; it just literally highlights the emptying of the bowl, not specifically the act of eating.