Why some Korean words are not pronounced as they are written? 2/3

The pronunciation of 의 changes depending on its location.

1) When 의 is located in the first syllable of a word, it is pronounced as written.

의자 - [의자],  의사 - [의사]

2) When 의 is located in the second syllable, it is pronounced as [].

채식주의- [채식주이],  수의사 - [수이사] 

3) When 의 is located as a possessive, it is pronounced as [].

친구의 책 - [친구에 책],  아이의 이름[아이에 이름]