There’s nothing like an uplifting classical mass with full choral and orchestral forces to uplift the soul after a year of pandemic restrictions and for some social isolation. Key Chorale’s new online program “Coronation: Mozart & Haydn” is a crowning achievement and well worth pulling up more than once. Josef Haydn and Wolfgang Amadeus Mozart were contemporaries, friends, mentor and mentee. The younger Mozart composed his Coronation Mass, KV 317 in 1779 for an Easter service at Salzburg Cathedral, although the mass got its name from a second performance for the coronation of the Holy Roman Emperor Francis II. There is a gracious elegance that shines through this score and is well captured by the chamber singers and orchestra under the vigorous leadership of conductor Joseph Caulkins.