Chi fan is a generic term for eating. Although you can have 'chi' as its own verb and you can eat lots of things.
chi wu fan le mei you? = did you eat lunch
ni you mei you chi fan? = did you eat?
ni you mei you chi mi fan = did you eat rice
Slightly different. Remember that in chinese if you want to be proper, you need to use two character phrases, one character "words" can be ambiguous.