Við frystum súpuna, þar sem við ætlum ekki að borða hana í dag.

Frystum is the 1st person plural form of frysta (to freeze), so it means we freeze / we are freezing or we froze, depending on context.

This is one of those Icelandic verb forms that can be ambiguous by itself. In this sentence, the present-time reading is the most natural because the second clause talks about today and about what we are not going to do:

• við frystum = we freeze / are freezing or we froze
• við ætlum ekki að borða hana í dag = we are not going to eat it today

So here a learner will usually understand frystum as something like we’re freezing.

Because súpuna is the form needed for the soup as a direct object.

The verb frysta takes an object, and that object is normally in the accusative. Also, the sentence is talking about the soup, not just soup in general.

For this noun:

• súpa = soup (indefinite)
• súpan = the soup (nominative)
• súpuna = the soup (accusative)

So Við frystum súpuna means we freeze/froze the soup, with súpuna as the object.

Because hana is the correct object pronoun for a feminine singular noun in the accusative.

The noun súpa is grammatically feminine in Icelandic. When you refer back to it with it, Icelandic uses a pronoun that matches its grammatical gender:

• súpa = feminine noun
• hana = it / her (feminine singular accusative)

So:

• að borða hana = to eat it

English uses it for things, but Icelandic uses gendered pronouns much more regularly. That is why you do not get það here.

Here þar sem is a conjunction meaning since, as, or because.

Even though þar sem can sometimes literally relate to where, in this sentence it introduces a reason:

• Við frystum súpuna, þar sem...
  = We’re freezing the soup, since / because...

So in this sentence, you should think of þar sem as a way to connect the main clause to the explanation.

This is the very common pattern:

• ætla að + infinitive

It means to intend to do something or to be going to do something.

So:

• við ætlum að borða = we intend to eat / we are going to eat
• við ætlum ekki að borða = we are not going to eat

Here:

• ætlum = we intend / are going
• að = particle used before the infinitive
• borða = eat

So að is not optional here; it belongs to the verb pattern ætla að + infinitive.

Because ekki usually comes after the finite verb in a normal Icelandic clause.

In this part of the sentence, the finite verb is ætlum:

• við ætlum ekki að borða hana í dag

That is the normal order:

• subject: við
• finite verb: ætlum
• negation: ekki
• infinitive phrase: að borða hana

So a learner should get used to the pattern:

• Ég tala ekki
• Við ætlum ekki að fara
• Hann getur ekki komið

Because þar sem introduces a subordinate clause, and subordinate clauses in Icelandic do not follow the usual main-clause verb-second pattern in the same way.

In the subordinate clause, the order is naturally:

• þar sem við ætlum ekki að borða hana í dag

with the subject við before the finite verb ætlum.

Compare:

• Main clause: Í dag ætlum við ekki að borða hana.
• Subordinate clause: þar sem við ætlum ekki að borða hana í dag

So this sentence is a good example of the difference between main-clause word order and subordinate-clause word order in Icelandic.

Because Icelandic normally needs an explicit subject in each clause.

So you get:

• Við frystum súpuna
• þar sem við ætlum ekki að borða hana í dag

Even though English also repeats we here, learners coming from some other languages sometimes expect the second subject to be omitted. In Icelandic, that would usually not work in a sentence like this. The subordinate clause needs its own subject, so við appears again.

Í dag is a very common time expression meaning today.

Literally, it is:

• í = in
• dag = a form of day

But as a whole, it functions just like the English adverb today.

It often appears at the end of the clause, as here:

• við ætlum ekki að borða hana í dag

It can also be moved for emphasis:

• Í dag ætlum við ekki að borða hana.

So this is a useful phrase to learn as a chunk.

Yes. Af því að is another very common way to say because.

So you could say:

• Við frystum súpuna, af því að við ætlum ekki að borða hana í dag.

That would be very natural too.

A rough difference is:

• þar sem can sound a bit like since / as
• af því að is a very direct because

In many everyday contexts, though, both work well.

Because once súpuna has already been mentioned, Icelandic usually prefers the pronoun hana, just as English prefers it:

• borða súpuna = eat the soup
• borða hana = eat it

Repeating súpuna would still be possible in some contexts, but it would sound more repetitive:

• ...við ætlum ekki að borða súpuna í dag

Using hana is the normal, natural way to refer back to the same noun.