what is going on in measure 6 and and the voice-leading of an augmented 4th movement to C in the alto?
In measure 14, that jump to middle C in the alto does not sit well with me. Have you tried an octave higher? It sounded better to me when I changed it.
I'm not so sure spelling out the chords melodically is such a good idea either. I don't think the singers would like and I am not sure it is very good voice leading either.
Other than that, it seemed like a good first time out. I didn't really analyze it harmonically outside of what I could hear and see right off that bat as potential areas of consideration.
I've never written vocal music, but one of my musical goals is to write a requiem and a mass, so I've seen a Kyrie or two. I think it is most important to pay attention to voice leading when dealing with the human voice because it does not have as much dexterity as all of the other instruments. In that you can't make as drastic of a change in melodic direction and leap taking as you could with say a woodwind, let alone a piano.
Did you model this off of any Kyrie in particular or was this just "free-hand"? If you are not familiar, may I suggest Faure's Kyrie from his requiem for assistance in molding your next one.