English spelling is inconsistent and strange sometimes. Part of the reason is that English was formed by borrowing many words from other languages. So we have a mix of spelling rules that are sometimes unpredictable. Good luck!

I beg to differ with the first answer to this question but the vast majority of words where the ch is pronounced as a k are from Greek, not Latin. Unfortunately, the correct pronunciation is something that a person just has to learn. I have heard very educated people pronounce ch like the ch in change when it should be pronounced like a k. Chemistry, chronicle, character, schism etc. There are many similar words.

We pronounce the CH sound as a k , when the origin of the word is Latin.