There is a "rule" I learned in second or third grade, though often pooh-poohed of late by "authorities":
A vowel in an "open" syllable (one that ends with the vowel) is "long", while a vowel in a "closed" syllable (one that ends with a consonant) is "short". However there's a special case for a word that ends in a consonant followed by a silent "e" (as in "ape") -- in that case the vowel (the "a") is "long". (This rule works pretty well for "a" sounds and "i" sounds, and not so well for "o" sounds.)
And, for those that have forgotten what was common knowledge 50 years ago, a long "a" sounds like the one in "late" or "gate" or "ape", while a short "a" sounds like the one in "cat" or "hat" or "chap".
And you know that the word "chapel" is (probably) not pronounced "chape-l" because English spelling is at least fairly regular about having syllables that contain at least one vowel in the standard spelling.
Even people who have never explicitly been taught these rules tend to learn them by osmosis over the decades, and so most experienced English speakers can usually approach a "normal" but unfamiliar word and do a pretty good job of pronouncing it, without having to consult a dictionary.
But, of course, in English there are no rules.