Questions & Answers about Ich habe es eilig, weil ich den Zug verpasst habe.
Why is there an es in Ich habe es eilig? Is it replacing a specific noun?
No, this is a dummy object. In the fixed expression es eilig haben (to be in a hurry), es doesn't replace a specific noun. It just fills the grammatical slot of the direct object, somewhat like how we say 'take it easy' in English.
Could I leave out the es and just say Ich bin eilig or Ich habe eilig?
No, es eilig haben is a strict set phrase. German uses haben (to have) rather than sein (to be) for this idiom. If you drop es, the sentence breaks because haben requires a direct object. You must include the dummy es.
I always mix up verbs for missing things. Why use verpasst here instead of vermisst?
You use verpassen when you miss an event, a deadline, or transportation like den Zug (the train). You use vermissen when you emotionally miss a person, a pet, or a place.
In the second clause, why is habe placed after the past participle verpasst?
The word weil is a subordinating conjunction, which means it forces the conjugated verb to the very end of its clause. Here, the conjugated helping verb habe is pushed to the absolute end, right after the past participle verpasst.