Chaka Khan announced her solo freedom with “I’m Every Woman,” the euphoric opening track on 1978’s Chaka. At 25 years old, Khan was already a veteran of the funk-rock band Rufus with whom she had recorded landmark hits like “Tell Me Something Good” and “Sweet Thing,” but Chaka took her passionate style in a new, mainstream R&B direction. The Warner Bros. album, produced by the legendarily versatile Arif Mardin (Dusty Springfield, Bette Midler, The Bee Gees), placed Khan’s powerful voice front and center with the support of the cream of New York’s…