word choice - Still trying to get my head around に and で

I've been trying to understand those two particles when applied to these phrases:

1. 私は朝ご飯にお茶を飲みます


2. 私は朝ご飯でお茶を飲みます


3. 私は朝ご飯の時にお茶を飲みます

What I more or less understand is:

1. the only/main thing I have for breakfast


2. at breakfast time, but not at any other time


3. at breakfast time, but not restricted to that time.

So, my questions are:

• What general function does に fulfill in sentence 1 (specific time, direction...)?


• Is, in sentence 1, 朝ご飯 functioning as a time expression?


• In sentence 2, is 朝ご飯 functioning as a time expression and じ indicating a restrictive period of time?

Answer

In sentence 1, に is not functioning as a time expression. It's like for or as. "I have green tea for breakfast."

で when used as a time particle can indicate:

1. 
   

   the age at which something was done: ２５歳で日本に行きました。At the age of 25 I went to Japan.

   
   


2. 
   

   the end point of a period of time: １時間で宿題を終えた。I finished my homework in/after an hour.
   Neither of these apply in sentence 2 so 朝ごはん is not functioning as a time expression. The で is showing that 朝ごはん is the place/setting where the tea-drinking is taking place.

   
   

In sentence 3, 朝ごはん itself is not a time expression, but together with 時 (とき not じ）you get 朝ごはんの時 'the time of breakfast' or 'breakfast time'.

Only one doubt I have: what does に indicate in the first sentence?

In sentence 1 に means for or as. It functions like として.